Hello,
The patches in this series contain mostly changes suggested by Daniel Vetter Thomas Zimmermann. They aim to fix existing races between the Generic System Framebuffer (sysfb) infrastructure and the fbdev and DRM device registration.
For example, it is currently possible for sysfb to register a platform device after a real DRM driver was registered and requested to remove the conflicting framebuffers. Or is possible for a simple{fb,drm} to match with a device previously registered by sysfb, even after a real driver is present.
A symptom of this issue, was worked around with the commit fb561bf9abde ("fbdev: Prevent probing generic drivers if a FB is already registered") but that's really a hack and should be reverted instead.
This series attempt to fix it more correctly and revert the mentioned hack. That will also allow to make the num_registered_fb variable not visible to drivers anymore, since that's internal to fbdev core.
Pach 1 is just a simple cleanup in preparation for later patches.
Patch 2 add a sysfb_disable() and sysfb_try_unregister() helpers to allow disabling sysfb and attempt to unregister registered devices respectively.
Patch 3 changes how is dealt with conflicting framebuffers unregistering, rather than having a variable to determine if a lock should be take, it just drops the lock before unregistering the platform device.
Patch 4 changes the fbdev core to not attempt to unregister devices that were registered by sysfb, let the same code doing the registration to also handle the unregistration.
Patch 5 fixes the race that exists between sysfb devices registration and fbdev framebuffer devices registration, by disabling the sysfb when a DRM or fbdev driver requests to remove conflicting framebuffers.
Patch 6 is the revert patch that was posted by Daniel before but dropped from his set and finally patch 7 is the one that makes num_registered_fb private to fbmem.c, to not allow drivers to use it anymore.
The patches were tested on a rpi4 with the vc4, simpledrm and simplefb drivers, using different combinations of built-in and as a module.
For example, having simpledrm as a module and loading it after the vc4 driver probed would not register a DRM device, which happens now without the patches from this series.
Best regards, Javier
Changes in v5: - Move the sysfb_disable() call at conflicting framebuffers again to avoid the need of a DRIVER_FIRMWARE capability flag. - Add Daniel Vetter's Reviewed-by tag again since reverted to the old patch that he already reviewed in v2. - Drop patches that added a DRM_FIRMWARE capability and use them since the case those prevented could be ignored (Daniel Vetter).
Changes in v4: - Make sysfb_disable() to also attempt to unregister a device. - Drop call to sysfb_disable() in fbmem since is done in other places now. - Add patch to make registered_fb[] private. - Add patches that introduce the DRM_FIRMWARE capability and usage.
Changes in v3: - Add Thomas Zimmermann's Reviewed-by tag to patch #1. - Call sysfb_disable() when a DRM dev and a fbdev are registered rather than when conflicting framebuffers are removed (Thomas Zimmermann). - Call sysfb_disable() when a fbdev framebuffer is registered rather than when conflicting framebuffers are removed (Thomas Zimmermann). - Drop Daniel Vetter's Reviewed-by tag since patch changed a lot. - Rebase on top of latest drm-misc-next branch.
Changes in v2: - Rebase on top of latest drm-misc-next and fix conflicts (Daniel Vetter). - Add kernel-doc comments and include in other_interfaces.rst (Daniel Vetter). - Explain in the commit message that fbmem has to unregister the device as fallback if a driver registered the device itself (Daniel Vetter). - Also explain that fallback in a comment in the code (Daniel Vetter). - Don't encode in fbmem the assumption that sysfb will always register platform devices (Daniel Vetter). - Add a FIXME comment about drivers registering devices (Daniel Vetter). - Explain in the commit message that fbmem has to unregister the device as fallback if a driver registered the device itself (Daniel Vetter). - Also explain that fallback in a comment in the code (Daniel Vetter). - Don't encode in fbmem the assumption that sysfb will always register platform devices (Daniel Vetter). - Add a FIXME comment about drivers registering devices (Daniel Vetter). - Drop RFC prefix since patches were already reviewed by Daniel Vetter. - Add Daniel Reviewed-by tags to the patches.
Daniel Vetter (2): Revert "fbdev: Prevent probing generic drivers if a FB is already registered" fbdev: Make registered_fb[] private to fbmem.c
Javier Martinez Canillas (5): firmware: sysfb: Make sysfb_create_simplefb() return a pdev pointer firmware: sysfb: Add helpers to unregister a pdev and disable registration fbdev: Restart conflicting fb removal loop when unregistering devices fbdev: Make sysfb to unregister its own registered devices fbdev: Disable sysfb device registration when removing conflicting FBs
.../driver-api/firmware/other_interfaces.rst | 6 ++ drivers/firmware/sysfb.c | 91 +++++++++++++++++-- drivers/firmware/sysfb_simplefb.c | 16 ++-- drivers/video/fbdev/core/fbmem.c | 67 +++++++++++--- drivers/video/fbdev/efifb.c | 11 --- drivers/video/fbdev/simplefb.c | 11 --- include/linux/fb.h | 8 +- include/linux/sysfb.h | 29 +++++- 8 files changed, 178 insertions(+), 61 deletions(-)
This function just returned 0 on success or an errno code on error, but it could be useful for sysfb_init() callers to have a pointer to the device.
Signed-off-by: Javier Martinez Canillas javierm@redhat.com Reviewed-by: Daniel Vetter daniel.vetter@ffwll.ch Reviewed-by: Thomas Zimmermann tzimmermann@suse.de
---
(no changes since v3)
Changes in v3: - Add Thomas Zimmermann's Reviewed-by tag to patch #1.
Changes in v2: - Rebase on top of latest drm-misc-next and fix conflicts (Daniel Vetter).
drivers/firmware/sysfb.c | 4 ++-- drivers/firmware/sysfb_simplefb.c | 16 ++++++++-------- include/linux/sysfb.h | 10 +++++----- 3 files changed, 15 insertions(+), 15 deletions(-)
diff --git a/drivers/firmware/sysfb.c b/drivers/firmware/sysfb.c index 2bfbb05f7d89..b032f40a92de 100644 --- a/drivers/firmware/sysfb.c +++ b/drivers/firmware/sysfb.c @@ -46,8 +46,8 @@ static __init int sysfb_init(void) /* try to create a simple-framebuffer device */ compatible = sysfb_parse_mode(si, &mode); if (compatible) { - ret = sysfb_create_simplefb(si, &mode); - if (!ret) + pd = sysfb_create_simplefb(si, &mode); + if (!IS_ERR(pd)) return 0; }
diff --git a/drivers/firmware/sysfb_simplefb.c b/drivers/firmware/sysfb_simplefb.c index bda8712bfd8c..a353e27f83f5 100644 --- a/drivers/firmware/sysfb_simplefb.c +++ b/drivers/firmware/sysfb_simplefb.c @@ -57,8 +57,8 @@ __init bool sysfb_parse_mode(const struct screen_info *si, return false; }
-__init int sysfb_create_simplefb(const struct screen_info *si, - const struct simplefb_platform_data *mode) +__init struct platform_device *sysfb_create_simplefb(const struct screen_info *si, + const struct simplefb_platform_data *mode) { struct platform_device *pd; struct resource res; @@ -76,7 +76,7 @@ __init int sysfb_create_simplefb(const struct screen_info *si, base |= (u64)si->ext_lfb_base << 32; if (!base || (u64)(resource_size_t)base != base) { printk(KERN_DEBUG "sysfb: inaccessible VRAM base\n"); - return -EINVAL; + return ERR_PTR(-EINVAL); }
/* @@ -93,7 +93,7 @@ __init int sysfb_create_simplefb(const struct screen_info *si, length = mode->height * mode->stride; if (length > size) { printk(KERN_WARNING "sysfb: VRAM smaller than advertised\n"); - return -EINVAL; + return ERR_PTR(-EINVAL); } length = PAGE_ALIGN(length);
@@ -104,11 +104,11 @@ __init int sysfb_create_simplefb(const struct screen_info *si, res.start = base; res.end = res.start + length - 1; if (res.end <= res.start) - return -EINVAL; + return ERR_PTR(-EINVAL);
pd = platform_device_alloc("simple-framebuffer", 0); if (!pd) - return -ENOMEM; + return ERR_PTR(-ENOMEM);
sysfb_apply_efi_quirks(pd);
@@ -124,10 +124,10 @@ __init int sysfb_create_simplefb(const struct screen_info *si, if (ret) goto err_put_device;
- return 0; + return pd;
err_put_device: platform_device_put(pd);
- return ret; + return ERR_PTR(ret); } diff --git a/include/linux/sysfb.h b/include/linux/sysfb.h index b0dcfa26d07b..708152e9037b 100644 --- a/include/linux/sysfb.h +++ b/include/linux/sysfb.h @@ -72,8 +72,8 @@ static inline void sysfb_apply_efi_quirks(struct platform_device *pd)
bool sysfb_parse_mode(const struct screen_info *si, struct simplefb_platform_data *mode); -int sysfb_create_simplefb(const struct screen_info *si, - const struct simplefb_platform_data *mode); +struct platform_device *sysfb_create_simplefb(const struct screen_info *si, + const struct simplefb_platform_data *mode);
#else /* CONFIG_SYSFB_SIMPLE */
@@ -83,10 +83,10 @@ static inline bool sysfb_parse_mode(const struct screen_info *si, return false; }
-static inline int sysfb_create_simplefb(const struct screen_info *si, - const struct simplefb_platform_data *mode) +static inline struct platform_device *sysfb_create_simplefb(const struct screen_info *si, + const struct simplefb_platform_data *mode) { - return -EINVAL; + return ERR_PTR(-EINVAL); }
#endif /* CONFIG_SYSFB_SIMPLE */
On 5/11/22 13:24, Javier Martinez Canillas wrote:
This function just returned 0 on success or an errno code on error, but it could be useful for sysfb_init() callers to have a pointer to the device.
Signed-off-by: Javier Martinez Canillas javierm@redhat.com Reviewed-by: Daniel Vetter daniel.vetter@ffwll.ch Reviewed-by: Thomas Zimmermann tzimmermann@suse.de
Thomas,
This patch can also be merged already if you want to shrink the set more. Even though no caller would use the new return value yet, it is a standalone change and already reviewed by Daniel and you.
These can be used by subsystems to unregister a platform device registered by sysfb and also to disable future platform device registration in sysfb.
Suggested-by: Daniel Vetter daniel.vetter@ffwll.ch Signed-off-by: Javier Martinez Canillas javierm@redhat.com Reviewed-by: Daniel Vetter daniel.vetter@ffwll.ch ---
(no changes since v4)
Changes in v4: - Make sysfb_disable() to also attempt to unregister a device.
Changes in v2: - Add kernel-doc comments and include in other_interfaces.rst (Daniel Vetter).
.../driver-api/firmware/other_interfaces.rst | 6 ++ drivers/firmware/sysfb.c | 87 +++++++++++++++++-- include/linux/sysfb.h | 19 ++++ 3 files changed, 106 insertions(+), 6 deletions(-)
diff --git a/Documentation/driver-api/firmware/other_interfaces.rst b/Documentation/driver-api/firmware/other_interfaces.rst index b81794e0cfbb..06ac89adaafb 100644 --- a/Documentation/driver-api/firmware/other_interfaces.rst +++ b/Documentation/driver-api/firmware/other_interfaces.rst @@ -13,6 +13,12 @@ EDD Interfaces .. kernel-doc:: drivers/firmware/edd.c :internal:
+Generic System Framebuffers Interface +------------------------------------- + +.. kernel-doc:: drivers/firmware/sysfb.c + :export: + Intel Stratix10 SoC Service Layer --------------------------------- Some features of the Intel Stratix10 SoC require a level of privilege diff --git a/drivers/firmware/sysfb.c b/drivers/firmware/sysfb.c index b032f40a92de..6768968949e6 100644 --- a/drivers/firmware/sysfb.c +++ b/drivers/firmware/sysfb.c @@ -34,21 +34,92 @@ #include <linux/screen_info.h> #include <linux/sysfb.h>
+static struct platform_device *pd; +static DEFINE_MUTEX(disable_lock); +static bool disabled; + +static bool sysfb_unregister(void) +{ + if (IS_ERR_OR_NULL(pd)) + return false; + + platform_device_unregister(pd); + pd = NULL; + + return true; +} + +/** + * sysfb_disable() - disable the Generic System Framebuffers support + * + * This disables the registration of system framebuffer devices that match the + * generic drivers that make use of the system framebuffer set up by firmware. + * + * It also unregisters a device if this was already registered by sysfb_init(). + * + * Context: The function can sleep. A @disable_lock mutex is acquired to serialize + * against sysfb_init(), that registers a system framebuffer device and + * sysfb_try_unregister(), that tries to unregister a framebuffer device. + */ +void sysfb_disable(void) +{ + mutex_lock(&disable_lock); + sysfb_unregister(); + disabled = true; + mutex_unlock(&disable_lock); +} +EXPORT_SYMBOL_GPL(sysfb_disable); + +/** + * sysfb_try_unregister() - attempt to unregister a system framebuffer device + * @dev: device to unregister + * + * This tries to unregister a system framebuffer device if this was registered + * by the Generic System Framebuffers. The device will only be unregistered if + * it was registered by sysfb_init(), otherwise it will not be unregistered. + * + * Context: The function can sleep. a @load_lock mutex is acquired to serialize + * against sysfb_init(), that registers a simple framebuffer device and + * sysfb_disable(), that disables the Generic System Framebuffers support. + * + * Return: + * * true - the device was unregistered successfully + * * false - the device was not unregistered + */ +bool sysfb_try_unregister(struct device *dev) +{ + bool ret = false; + + mutex_lock(&disable_lock); + if (IS_ERR_OR_NULL(pd) || pd != to_platform_device(dev)) + goto unlock_mutex; + + ret = sysfb_unregister(); + +unlock_mutex: + mutex_unlock(&disable_lock); + return ret; +} +EXPORT_SYMBOL_GPL(sysfb_try_unregister); + static __init int sysfb_init(void) { struct screen_info *si = &screen_info; struct simplefb_platform_data mode; - struct platform_device *pd; const char *name; bool compatible; - int ret; + int ret = 0; + + mutex_lock(&disable_lock); + if (disabled) + goto unlock_mutex;
/* try to create a simple-framebuffer device */ compatible = sysfb_parse_mode(si, &mode); if (compatible) { pd = sysfb_create_simplefb(si, &mode); if (!IS_ERR(pd)) - return 0; + goto unlock_mutex; }
/* if the FB is incompatible, create a legacy framebuffer device */ @@ -60,8 +131,10 @@ static __init int sysfb_init(void) name = "platform-framebuffer";
pd = platform_device_alloc(name, 0); - if (!pd) - return -ENOMEM; + if (!pd) { + ret = -ENOMEM; + goto unlock_mutex; + }
sysfb_apply_efi_quirks(pd);
@@ -73,9 +146,11 @@ static __init int sysfb_init(void) if (ret) goto err;
- return 0; + goto unlock_mutex; err: platform_device_put(pd); +unlock_mutex: + mutex_unlock(&disable_lock); return ret; }
diff --git a/include/linux/sysfb.h b/include/linux/sysfb.h index 708152e9037b..e8c0313fac8f 100644 --- a/include/linux/sysfb.h +++ b/include/linux/sysfb.h @@ -55,6 +55,25 @@ struct efifb_dmi_info { int flags; };
+#ifdef CONFIG_SYSFB + +void sysfb_disable(void); +bool sysfb_try_unregister(struct device *dev); + +#else /* CONFIG_SYSFB */ + +static inline void sysfb_disable(void) +{ + +} + +static inline bool sysfb_try_unregister(struct device *dev) +{ + return false; +} + +#endif /* CONFIG_SYSFB */ + #ifdef CONFIG_EFI
extern struct efifb_dmi_info efifb_dmi_list[];
Hi
Am 11.05.22 um 13:24 schrieb Javier Martinez Canillas:
These can be used by subsystems to unregister a platform device registered by sysfb and also to disable future platform device registration in sysfb.
I find it very hard to review these patches, as related things are put into separate patches.
I suggest to put the sysfb_disable() stuff into patch 5 and the rest into patch 4.
Best regards Thomas
Suggested-by: Daniel Vetter daniel.vetter@ffwll.ch Signed-off-by: Javier Martinez Canillas javierm@redhat.com Reviewed-by: Daniel Vetter daniel.vetter@ffwll.ch
(no changes since v4)
Changes in v4:
- Make sysfb_disable() to also attempt to unregister a device.
Changes in v2:
Add kernel-doc comments and include in other_interfaces.rst (Daniel Vetter).
.../driver-api/firmware/other_interfaces.rst | 6 ++ drivers/firmware/sysfb.c | 87 +++++++++++++++++-- include/linux/sysfb.h | 19 ++++ 3 files changed, 106 insertions(+), 6 deletions(-)
diff --git a/Documentation/driver-api/firmware/other_interfaces.rst b/Documentation/driver-api/firmware/other_interfaces.rst index b81794e0cfbb..06ac89adaafb 100644 --- a/Documentation/driver-api/firmware/other_interfaces.rst +++ b/Documentation/driver-api/firmware/other_interfaces.rst @@ -13,6 +13,12 @@ EDD Interfaces .. kernel-doc:: drivers/firmware/edd.c :internal:
+Generic System Framebuffers Interface +-------------------------------------
+.. kernel-doc:: drivers/firmware/sysfb.c
- :export:
Intel Stratix10 SoC Service Layer
Some features of the Intel Stratix10 SoC require a level of privilegediff --git a/drivers/firmware/sysfb.c b/drivers/firmware/sysfb.c index b032f40a92de..6768968949e6 100644 --- a/drivers/firmware/sysfb.c +++ b/drivers/firmware/sysfb.c @@ -34,21 +34,92 @@ #include <linux/screen_info.h> #include <linux/sysfb.h>
+static struct platform_device *pd; +static DEFINE_MUTEX(disable_lock); +static bool disabled;
+static bool sysfb_unregister(void) +{
- if (IS_ERR_OR_NULL(pd))
return false;- platform_device_unregister(pd);
- pd = NULL;
- return true;
+}
+/**
- sysfb_disable() - disable the Generic System Framebuffers support
- This disables the registration of system framebuffer devices that match the
- generic drivers that make use of the system framebuffer set up by firmware.
- It also unregisters a device if this was already registered by sysfb_init().
- Context: The function can sleep. A @disable_lock mutex is acquired to serialize
against sysfb_init(), that registers a system framebuffer device and
sysfb_try_unregister(), that tries to unregister a framebuffer device.- */
+void sysfb_disable(void) +{
- mutex_lock(&disable_lock);
- sysfb_unregister();
- disabled = true;
- mutex_unlock(&disable_lock);
+} +EXPORT_SYMBOL_GPL(sysfb_disable);
+/**
- sysfb_try_unregister() - attempt to unregister a system framebuffer device
- @dev: device to unregister
- This tries to unregister a system framebuffer device if this was registered
- by the Generic System Framebuffers. The device will only be unregistered if
- it was registered by sysfb_init(), otherwise it will not be unregistered.
- Context: The function can sleep. a @load_lock mutex is acquired to serialize
against sysfb_init(), that registers a simple framebuffer device and
sysfb_disable(), that disables the Generic System Framebuffers support.
- Return:
- true - the device was unregistered successfully
- false - the device was not unregistered
- */
+bool sysfb_try_unregister(struct device *dev) +{
- bool ret = false;
- mutex_lock(&disable_lock);
- if (IS_ERR_OR_NULL(pd) || pd != to_platform_device(dev))
goto unlock_mutex;- ret = sysfb_unregister();
+unlock_mutex:
- mutex_unlock(&disable_lock);
- return ret;
+} +EXPORT_SYMBOL_GPL(sysfb_try_unregister);
- static __init int sysfb_init(void) { struct screen_info *si = &screen_info; struct simplefb_platform_data mode;
- struct platform_device *pd; const char *name; bool compatible;
- int ret;
int ret = 0;
mutex_lock(&disable_lock);
if (disabled)
goto unlock_mutex;/* try to create a simple-framebuffer device */ compatible = sysfb_parse_mode(si, &mode); if (compatible) { pd = sysfb_create_simplefb(si, &mode); if (!IS_ERR(pd))
return 0;
goto unlock_mutex;}
/* if the FB is incompatible, create a legacy framebuffer device */
@@ -60,8 +131,10 @@ static __init int sysfb_init(void) name = "platform-framebuffer";
pd = platform_device_alloc(name, 0);
- if (!pd)
return -ENOMEM;
if (!pd) {
ret = -ENOMEM;goto unlock_mutex;}
sysfb_apply_efi_quirks(pd);
@@ -73,9 +146,11 @@ static __init int sysfb_init(void) if (ret) goto err;
- return 0;
- goto unlock_mutex; err: platform_device_put(pd);
+unlock_mutex:
- mutex_unlock(&disable_lock); return ret; }
diff --git a/include/linux/sysfb.h b/include/linux/sysfb.h index 708152e9037b..e8c0313fac8f 100644 --- a/include/linux/sysfb.h +++ b/include/linux/sysfb.h @@ -55,6 +55,25 @@ struct efifb_dmi_info { int flags; };
+#ifdef CONFIG_SYSFB
+void sysfb_disable(void); +bool sysfb_try_unregister(struct device *dev);
+#else /* CONFIG_SYSFB */
+static inline void sysfb_disable(void) +{
+}
+static inline bool sysfb_try_unregister(struct device *dev) +{
- return false;
+}
+#endif /* CONFIG_SYSFB */
#ifdef CONFIG_EFI
extern struct efifb_dmi_info efifb_dmi_list[];
Hello Thomas,
On 5/11/22 13:54, Thomas Zimmermann wrote:
Hi
Am 11.05.22 um 13:24 schrieb Javier Martinez Canillas:
These can be used by subsystems to unregister a platform device registered by sysfb and also to disable future platform device registration in sysfb.
I find it very hard to review these patches, as related things are put into separate patches.
I suggest to put the sysfb_disable() stuff into patch 5 and the rest into patch 4.
Ok, you then want in the same patch to have both the helper definition and first usage.
Other subsystems ask you to do the opposite, to split the definition and usage in separate patches. But I'm fine with merging those if you prefer.
Best regards Thomas
Hi
Am 11.05.22 um 14:01 schrieb Javier Martinez Canillas:
Hello Thomas,
On 5/11/22 13:54, Thomas Zimmermann wrote:
Hi
Am 11.05.22 um 13:24 schrieb Javier Martinez Canillas:
These can be used by subsystems to unregister a platform device registered by sysfb and also to disable future platform device registration in sysfb.
I find it very hard to review these patches, as related things are put into separate patches.
I suggest to put the sysfb_disable() stuff into patch 5 and the rest into patch 4.
Ok, you then want in the same patch to have both the helper definition and first usage.
Other subsystems ask you to do the opposite, to split the definition and usage in separate patches. But I'm fine with merging those if you prefer.
Usually, I have no strong opinion on this. But in the case of this specific patchset, I have the feeling that I'm missing some important point because call and implementation are separate. See my other replies for that. Putting them next to each other will hopefully help. Sorry for the inconvenience.
Best regards Thomas
Best regards Thomas
Hello Thomas,
On 5/11/22 14:05, Thomas Zimmermann wrote:
[snip]
Other subsystems ask you to do the opposite, to split the definition and usage in separate patches. But I'm fine with merging those if you prefer.
Usually, I have no strong opinion on this. But in the case of this specific patchset, I have the feeling that I'm missing some important point because call and implementation are separate. See my other replies for that. Putting them next to each other will hopefully help. Sorry for the inconvenience.
No worries at all. Happy to do that change if the patches are easy to understand. It took me some time as well to wrap my head around all the race conditions and needed locking.
Same for patch 3/7, but I'm convinced that dropping the lock is the correct thing to do than calling to drivers' .remove callbacks with a lock held.
Am 11.05.22 um 13:24 schrieb Javier Martinez Canillas:
These can be used by subsystems to unregister a platform device registered by sysfb and also to disable future platform device registration in sysfb.
Suggested-by: Daniel Vetter daniel.vetter@ffwll.ch Signed-off-by: Javier Martinez Canillas javierm@redhat.com Reviewed-by: Daniel Vetter daniel.vetter@ffwll.ch
(no changes since v4)
Changes in v4:
- Make sysfb_disable() to also attempt to unregister a device.
Changes in v2:
Add kernel-doc comments and include in other_interfaces.rst (Daniel Vetter).
.../driver-api/firmware/other_interfaces.rst | 6 ++ drivers/firmware/sysfb.c | 87 +++++++++++++++++-- include/linux/sysfb.h | 19 ++++ 3 files changed, 106 insertions(+), 6 deletions(-)
diff --git a/Documentation/driver-api/firmware/other_interfaces.rst b/Documentation/driver-api/firmware/other_interfaces.rst index b81794e0cfbb..06ac89adaafb 100644 --- a/Documentation/driver-api/firmware/other_interfaces.rst +++ b/Documentation/driver-api/firmware/other_interfaces.rst @@ -13,6 +13,12 @@ EDD Interfaces .. kernel-doc:: drivers/firmware/edd.c :internal:
+Generic System Framebuffers Interface +-------------------------------------
+.. kernel-doc:: drivers/firmware/sysfb.c
- :export:
Intel Stratix10 SoC Service Layer
Some features of the Intel Stratix10 SoC require a level of privilegediff --git a/drivers/firmware/sysfb.c b/drivers/firmware/sysfb.c index b032f40a92de..6768968949e6 100644 --- a/drivers/firmware/sysfb.c +++ b/drivers/firmware/sysfb.c @@ -34,21 +34,92 @@ #include <linux/screen_info.h> #include <linux/sysfb.h>
+static struct platform_device *pd; +static DEFINE_MUTEX(disable_lock); +static bool disabled;
+static bool sysfb_unregister(void) +{
- if (IS_ERR_OR_NULL(pd))
return false;- platform_device_unregister(pd);
- pd = NULL;
- return true;
+}
+/**
- sysfb_disable() - disable the Generic System Framebuffers support
- This disables the registration of system framebuffer devices that match the
- generic drivers that make use of the system framebuffer set up by firmware.
- It also unregisters a device if this was already registered by sysfb_init().
Why? I still cannot wrap my mind around, why we need to store *pd at all and use sysfb_try_unregister() for unregistering.
- Context: The function can sleep. A @disable_lock mutex is acquired to serialize
against sysfb_init(), that registers a system framebuffer device and
sysfb_try_unregister(), that tries to unregister a framebuffer device.- */
+void sysfb_disable(void) +{
- mutex_lock(&disable_lock);
- sysfb_unregister();
- disabled = true;
- mutex_unlock(&disable_lock);
+} +EXPORT_SYMBOL_GPL(sysfb_disable);
+/**
- sysfb_try_unregister() - attempt to unregister a system framebuffer device
- @dev: device to unregister
- This tries to unregister a system framebuffer device if this was registered
- by the Generic System Framebuffers. The device will only be unregistered if
- it was registered by sysfb_init(), otherwise it will not be unregistered.
- Context: The function can sleep. a @load_lock mutex is acquired to serialize
against sysfb_init(), that registers a simple framebuffer device and
sysfb_disable(), that disables the Generic System Framebuffers support.
- Return:
- true - the device was unregistered successfully
- false - the device was not unregistered
- */
+bool sysfb_try_unregister(struct device *dev)
As it stands, I strongly object the use of this function as still don't really get the purpose. It looks like a glorified wrapper around platform_device_unregister(). Do we need disable_lock to serialize with something else?
Best regards Thomas
+{
- bool ret = false;
- mutex_lock(&disable_lock);
- if (IS_ERR_OR_NULL(pd) || pd != to_platform_device(dev))
goto unlock_mutex;- ret = sysfb_unregister();
+unlock_mutex:
- mutex_unlock(&disable_lock);
- return ret;
+} +EXPORT_SYMBOL_GPL(sysfb_try_unregister);
- static __init int sysfb_init(void) { struct screen_info *si = &screen_info; struct simplefb_platform_data mode;
- struct platform_device *pd; const char *name; bool compatible;
- int ret;
int ret = 0;
mutex_lock(&disable_lock);
if (disabled)
goto unlock_mutex;/* try to create a simple-framebuffer device */ compatible = sysfb_parse_mode(si, &mode); if (compatible) { pd = sysfb_create_simplefb(si, &mode); if (!IS_ERR(pd))
return 0;
goto unlock_mutex;}
/* if the FB is incompatible, create a legacy framebuffer device */
@@ -60,8 +131,10 @@ static __init int sysfb_init(void) name = "platform-framebuffer";
pd = platform_device_alloc(name, 0);
- if (!pd)
return -ENOMEM;
if (!pd) {
ret = -ENOMEM;goto unlock_mutex;}
sysfb_apply_efi_quirks(pd);
@@ -73,9 +146,11 @@ static __init int sysfb_init(void) if (ret) goto err;
- return 0;
- goto unlock_mutex; err: platform_device_put(pd);
+unlock_mutex:
- mutex_unlock(&disable_lock); return ret; }
diff --git a/include/linux/sysfb.h b/include/linux/sysfb.h index 708152e9037b..e8c0313fac8f 100644 --- a/include/linux/sysfb.h +++ b/include/linux/sysfb.h @@ -55,6 +55,25 @@ struct efifb_dmi_info { int flags; };
+#ifdef CONFIG_SYSFB
+void sysfb_disable(void); +bool sysfb_try_unregister(struct device *dev);
+#else /* CONFIG_SYSFB */
+static inline void sysfb_disable(void) +{
+}
+static inline bool sysfb_try_unregister(struct device *dev) +{
- return false;
+}
+#endif /* CONFIG_SYSFB */
#ifdef CONFIG_EFI
extern struct efifb_dmi_info efifb_dmi_list[];
Hello Thomas,
On 5/11/22 14:02, Thomas Zimmermann wrote:
[snip]
+/**
- sysfb_disable() - disable the Generic System Framebuffers support
- This disables the registration of system framebuffer devices that match the
- generic drivers that make use of the system framebuffer set up by firmware.
- It also unregisters a device if this was already registered by sysfb_init().
Why? I still cannot wrap my mind around, why we need to store *pd at all and use sysfb_try_unregister() for unregistering.
Because on sysfb_disable(), the registered platform device has to unregistered.
And sysfb has no way to know if it was unregistered already or not unless that stage is maintained in sysfb itself.
Let's have some examples assuming that we don't have this helper in sysfb (will use the vc4 DRM driver just to avoid typing "a real DRM driver).
a) simplefb probed and then vc4
1) "simple-framebuffer" pdev is registered by sysfb 2) simplefb is registered and matches "simple-framebuffer" 3) a vc4 device is registered by OF when parsing the DTB 4) vc4 driver is registered, matches vc4 and probes 5) vc4 requests the conflicting framebuffers to be removed and fbmem unregisters "simple-framebuffer" 6) fbmem calls sysfb_disable() 7) sysfb_disable() should unregister the pdev but can't because has no way to know that fbmem already did that.
b) vc4 probed and then simplefb.ko module is loaded
1) "simple-framebuffer" pdev is registered by sysfb 2) a vc4 device is registered by OF when parsing the DTB 3) vc4 driver is registered, matches vc4 and probes 4) vc4 requests the conflicting framebuffers to be removed and fbmem unregisters "simple-framebuffer" 5) fbmem calls sysfb_disable() 6) sysfb_disable() should unregister the pdev but can't because has no way to know that fbmem already did that. 7) simplefb.ko is loaded and simplefb driver registered 8) simplefb matches the registered "simple-framebuffer" and will wrongly probe and register a DRM device.
In option (a), making sysfb_disable() to attempt to unregister the device that register in sysfb_init() will lead to a use-after-free if this was already unregistered by fbmem in remove_conflicting_framebuffers(), so it can't attempt to do that.
Same for option (b), but sysfb_disable() can't rely on fbmem to do the unregistration because it only does for devices that are associated with an already registered fbdev.
[snip]
- Return:
- true - the device was unregistered successfully
- false - the device was not unregistered
- */
+bool sysfb_try_unregister(struct device *dev)
As it stands, I strongly object the use of this function as still don't
No worries, it's my bad since I clearly failed to explain the rationale in the commit message and comments.
really get the purpose. It looks like a glorified wrapper around platform_device_unregister(). Do we need disable_lock to serialize with something else?
Yes, it has to serialize with sysfb_init() and sysfb_disable().
Best regards Thomas
Drivers that want to remove registered conflicting framebuffers prior to register their own framebuffer, calls remove_conflicting_framebuffers().
This function takes the registration_lock mutex, to prevent a races when drivers register framebuffer devices. But if a conflicting framebuffer device is found, the underlaying platform device is unregistered and this will lead to the platform driver .remove callback to be called, which in turn will call to the unregister_framebuffer() that takes the same lock.
To prevent this, a struct fb_info.forced_out field was used as indication to unregister_framebuffer() whether the mutex has to be grabbed or not.
A cleaner solution is to drop the lock before platform_device_unregister() so unregister_framebuffer() can take it when called from the fbdev driver, and just grab the lock again after the device has been registered and do a removal loop restart.
Since the framebuffer devices will already be removed, the loop would just finish when no more conflicting framebuffers are found.
Suggested-by: Daniel Vetter daniel.vetter@ffwll.ch Signed-off-by: Javier Martinez Canillas javierm@redhat.com Reviewed-by: Daniel Vetter daniel.vetter@ffwll.ch ---
(no changes since v1)
drivers/video/fbdev/core/fbmem.c | 22 +++++++++++++++------- include/linux/fb.h | 1 - 2 files changed, 15 insertions(+), 8 deletions(-)
diff --git a/drivers/video/fbdev/core/fbmem.c b/drivers/video/fbdev/core/fbmem.c index b445a7a00def..2fda5917c212 100644 --- a/drivers/video/fbdev/core/fbmem.c +++ b/drivers/video/fbdev/core/fbmem.c @@ -1555,6 +1555,7 @@ static void do_remove_conflicting_framebuffers(struct apertures_struct *a, { int i;
+restart_removal: /* check all firmware fbs and kick off if the base addr overlaps */ for_each_registered_fb(i) { struct apertures_struct *gen_aper; @@ -1587,12 +1588,23 @@ static void do_remove_conflicting_framebuffers(struct apertures_struct *a, pr_warn("fb%d: no device set\n", i); do_unregister_framebuffer(registered_fb[i]); } else if (dev_is_platform(device)) { - registered_fb[i]->forced_out = true; + /* + * Drop the lock because if the device is unregistered, its + * driver will call to unregister_framebuffer(), that takes + * this lock. + */ + mutex_unlock(®istration_lock); platform_device_unregister(to_platform_device(device)); + mutex_lock(®istration_lock); } else { pr_warn("fb%d: cannot remove device\n", i); do_unregister_framebuffer(registered_fb[i]); } + /* + * Restart the removal loop now that the device has been + * unregistered and its associated framebuffer gone. + */ + goto restart_removal; } } } @@ -1899,13 +1911,9 @@ EXPORT_SYMBOL(register_framebuffer); void unregister_framebuffer(struct fb_info *fb_info) { - bool forced_out = fb_info->forced_out; - - if (!forced_out) - mutex_lock(®istration_lock); + mutex_lock(®istration_lock); do_unregister_framebuffer(fb_info); - if (!forced_out) - mutex_unlock(®istration_lock); + mutex_unlock(®istration_lock); } EXPORT_SYMBOL(unregister_framebuffer);
diff --git a/include/linux/fb.h b/include/linux/fb.h index 69c67c70fa78..bbe1e4571899 100644 --- a/include/linux/fb.h +++ b/include/linux/fb.h @@ -511,7 +511,6 @@ struct fb_info { } *apertures;
bool skip_vt_switch; /* no VT switch on suspend/resume required */ - bool forced_out; /* set when being removed by another driver */ };
static inline struct apertures_struct *alloc_apertures(unsigned int max_num) {
Hi Javier
Am 11.05.22 um 13:30 schrieb Javier Martinez Canillas:
Drivers that want to remove registered conflicting framebuffers prior to register their own framebuffer, calls remove_conflicting_framebuffers().
This function takes the registration_lock mutex, to prevent a races when drivers register framebuffer devices. But if a conflicting framebuffer device is found, the underlaying platform device is unregistered and this will lead to the platform driver .remove callback to be called, which in turn will call to the unregister_framebuffer() that takes the same lock.
To prevent this, a struct fb_info.forced_out field was used as indication to unregister_framebuffer() whether the mutex has to be grabbed or not.
A cleaner solution is to drop the lock before platform_device_unregister() so unregister_framebuffer() can take it when called from the fbdev driver, and just grab the lock again after the device has been registered and do a removal loop restart.
Since the framebuffer devices will already be removed, the loop would just finish when no more conflicting framebuffers are found.
Suggested-by: Daniel Vetter daniel.vetter@ffwll.ch Signed-off-by: Javier Martinez Canillas javierm@redhat.com Reviewed-by: Daniel Vetter daniel.vetter@ffwll.ch
I'd like to shrink this patchset. This looks like it can be merged immediately?
Best regards Thomas
(no changes since v1)
drivers/video/fbdev/core/fbmem.c | 22 +++++++++++++++------- include/linux/fb.h | 1 - 2 files changed, 15 insertions(+), 8 deletions(-)
diff --git a/drivers/video/fbdev/core/fbmem.c b/drivers/video/fbdev/core/fbmem.c index b445a7a00def..2fda5917c212 100644 --- a/drivers/video/fbdev/core/fbmem.c +++ b/drivers/video/fbdev/core/fbmem.c @@ -1555,6 +1555,7 @@ static void do_remove_conflicting_framebuffers(struct apertures_struct *a, { int i;
+restart_removal: /* check all firmware fbs and kick off if the base addr overlaps */ for_each_registered_fb(i) { struct apertures_struct *gen_aper; @@ -1587,12 +1588,23 @@ static void do_remove_conflicting_framebuffers(struct apertures_struct *a, pr_warn("fb%d: no device set\n", i); do_unregister_framebuffer(registered_fb[i]); } else if (dev_is_platform(device)) {
registered_fb[i]->forced_out = true;
/** Drop the lock because if the device is unregistered, its* driver will call to unregister_framebuffer(), that takes* this lock.*/mutex_unlock(®istration_lock); platform_device_unregister(to_platform_device(device));mutex_lock(®istration_lock); } else { pr_warn("fb%d: cannot remove device\n", i); do_unregister_framebuffer(registered_fb[i]); }/** Restart the removal loop now that the device has been* unregistered and its associated framebuffer gone.*/goto restart_removal;@@ -1899,13 +1911,9 @@ EXPORT_SYMBOL(register_framebuffer); void unregister_framebuffer(struct fb_info *fb_info) {
- bool forced_out = fb_info->forced_out;
- if (!forced_out)
mutex_lock(®istration_lock);
- mutex_lock(®istration_lock); do_unregister_framebuffer(fb_info);
- if (!forced_out)
mutex_unlock(®istration_lock);
- mutex_unlock(®istration_lock); } EXPORT_SYMBOL(unregister_framebuffer);
diff --git a/include/linux/fb.h b/include/linux/fb.h index 69c67c70fa78..bbe1e4571899 100644 --- a/include/linux/fb.h +++ b/include/linux/fb.h @@ -511,7 +511,6 @@ struct fb_info { } *apertures;
bool skip_vt_switch; /* no VT switch on suspend/resume required */
bool forced_out; /* set when being removed by another driver */ };
static inline struct apertures_struct *alloc_apertures(unsigned int max_num) {
Hello Thomas,
On 5/11/22 13:47, Thomas Zimmermann wrote:
Hi Javier
Am 11.05.22 um 13:30 schrieb Javier Martinez Canillas:
Drivers that want to remove registered conflicting framebuffers prior to register their own framebuffer, calls remove_conflicting_framebuffers().
This function takes the registration_lock mutex, to prevent a races when drivers register framebuffer devices. But if a conflicting framebuffer device is found, the underlaying platform device is unregistered and this will lead to the platform driver .remove callback to be called, which in turn will call to the unregister_framebuffer() that takes the same lock.
To prevent this, a struct fb_info.forced_out field was used as indication to unregister_framebuffer() whether the mutex has to be grabbed or not.
A cleaner solution is to drop the lock before platform_device_unregister() so unregister_framebuffer() can take it when called from the fbdev driver, and just grab the lock again after the device has been registered and do a removal loop restart.
Since the framebuffer devices will already be removed, the loop would just finish when no more conflicting framebuffers are found.
Suggested-by: Daniel Vetter daniel.vetter@ffwll.ch Signed-off-by: Javier Martinez Canillas javierm@redhat.com Reviewed-by: Daniel Vetter daniel.vetter@ffwll.ch
I'd like to shrink this patchset. This looks like it can be merged
Same. At least this version dropped a few patches that we had in v4 (related to DRM_FIRMWARE capability flag).
immediately?
Yes, this one is independent of the others and could be merged already.
Best regards Thomas
On 5/11/22 13:30, Javier Martinez Canillas wrote:
Drivers that want to remove registered conflicting framebuffers prior to register their own framebuffer, calls remove_conflicting_framebuffers().
This function takes the registration_lock mutex, to prevent a races when drivers register framebuffer devices. But if a conflicting framebuffer device is found, the underlaying platform device is unregistered and this will lead to the platform driver .remove callback to be called, which in turn will call to the unregister_framebuffer() that takes the same lock.
To prevent this, a struct fb_info.forced_out field was used as indication to unregister_framebuffer() whether the mutex has to be grabbed or not.
A cleaner solution is to drop the lock before platform_device_unregister() so unregister_framebuffer() can take it when called from the fbdev driver, and just grab the lock again after the device has been registered and do a removal loop restart.
Since the framebuffer devices will already be removed, the loop would just finish when no more conflicting framebuffers are found.
Suggested-by: Daniel Vetter daniel.vetter@ffwll.ch Signed-off-by: Javier Martinez Canillas javierm@redhat.com Reviewed-by: Daniel Vetter daniel.vetter@ffwll.ch
Pushed this to drm-misc (drm-misc-next). Thanks all!
The platform devices registered in sysfb match with a firmware-based fbdev or DRM driver, that are used to have early graphics using framebuffers set up by the system firmware.
Real DRM drivers later are probed and remove all conflicting framebuffers, leading to these platform devices for generic drivers to be unregistered.
But the current solution has the problem that sysfb doesn't know when the device that registered is unregistered. This means that is not able to do any cleanup if needed since the device pointer may not be valid anymore.
Not all platforms use sysfb to register the simple framebuffer devices, so an unregistration has to be forced by fbmem if sysfb_try_unregister() does not succeed at unregister the device.
Suggested-by: Daniel Vetter daniel.vetter@ffwll.ch Signed-off-by: Javier Martinez Canillas javierm@redhat.com Reviewed-by: Daniel Vetter daniel.vetter@ffwll.ch
---
(no changes since v4)
Changes in v4: - Drop call to sysfb_disable() in fbmem since is done in other places now.
Changes in v2: - Explain in the commit message that fbmem has to unregister the device as fallback if a driver registered the device itself (Daniel Vetter). - Also explain that fallback in a comment in the code (Daniel Vetter). - Don't encode in fbmem the assumption that sysfb will always register platform devices (Daniel Vetter). - Add a FIXME comment about drivers registering devices (Daniel Vetter).
drivers/video/fbdev/core/fbmem.c | 28 +++++++++++++++++++++++----- 1 file changed, 23 insertions(+), 5 deletions(-)
diff --git a/drivers/video/fbdev/core/fbmem.c b/drivers/video/fbdev/core/fbmem.c index 2fda5917c212..9b035ef4d552 100644 --- a/drivers/video/fbdev/core/fbmem.c +++ b/drivers/video/fbdev/core/fbmem.c @@ -19,6 +19,7 @@ #include <linux/kernel.h> #include <linux/major.h> #include <linux/slab.h> +#include <linux/sysfb.h> #include <linux/mm.h> #include <linux/mman.h> #include <linux/vt.h> @@ -1587,18 +1588,35 @@ static void do_remove_conflicting_framebuffers(struct apertures_struct *a, if (!device) { pr_warn("fb%d: no device set\n", i); do_unregister_framebuffer(registered_fb[i]); - } else if (dev_is_platform(device)) { + } else { /* * Drop the lock because if the device is unregistered, its * driver will call to unregister_framebuffer(), that takes * this lock. */ mutex_unlock(®istration_lock); - platform_device_unregister(to_platform_device(device)); + /* + * First attempt the device to be unregistered by sysfb. + */ + if (!sysfb_try_unregister(device)) { + if (dev_is_platform(device)) { + /* + * FIXME: sysfb didn't register this device, the platform + * device was registered in other platform code. + */ + platform_device_unregister(to_platform_device(device)); + } else { + /* + * If is not a platform device, at least print a warning. A + * fix would add to make the code that registered the device + * to also unregister it. + */ + pr_warn("fb%d: cannot remove device\n", i); + /* call unregister_framebuffer() since the lock was dropped */ + unregister_framebuffer(registered_fb[i]); + } + } mutex_lock(®istration_lock); - } else { - pr_warn("fb%d: cannot remove device\n", i); - do_unregister_framebuffer(registered_fb[i]); } /* * Restart the removal loop now that the device has been
The platform devices registered by sysfb match with firmware-based DRM or fbdev drivers, that are used to have early graphics using a framebuffer provided by the system firmware.
DRM or fbdev drivers later are probed and remove all conflicting framebuffers, leading to these platform devices for generic drivers to be unregistered.
But the current solution has a race, since the sysfb_init() function could be called after a DRM or fbdev driver is probed and request to unregister the devices for drivers with conflicting framebuffes.
To prevent this, disable any future sysfb platform device registration by calling sysfb_disable(), if a driver requests to remove the conflicting framebuffers.
Suggested-by: Daniel Vetter daniel.vetter@ffwll.ch Signed-off-by: Javier Martinez Canillas javierm@redhat.com Reviewed-by: Daniel Vetter daniel.vetter@ffwll.ch ---
Changes in v5: - Move the sysfb_disable() call at conflicting framebuffers again to avoid the need of a DRIVER_FIRMWARE capability flag. - Add Daniel Vetter's Reviewed-by tag again since reverted to the old patch that he already reviewed in v2.
Changes in v3: - Call sysfb_disable() when a DRM dev and a fbdev are registered rather than when conflicting framebuffers are removed (Thomas Zimmermann). - Call sysfb_disable() when a fbdev framebuffer is registered rather than when conflicting framebuffers are removed (Thomas Zimmermann). - Drop Daniel Vetter's Reviewed-by tag since patch changed a lot.
Changes in v2: - Explain in the commit message that fbmem has to unregister the device as fallback if a driver registered the device itself (Daniel Vetter). - Also explain that fallback in a comment in the code (Daniel Vetter). - Don't encode in fbmem the assumption that sysfb will always register platform devices (Daniel Vetter). - Add a FIXME comment about drivers registering devices (Daniel Vetter).
drivers/video/fbdev/core/fbmem.c | 11 +++++++++++ 1 file changed, 11 insertions(+)
diff --git a/drivers/video/fbdev/core/fbmem.c b/drivers/video/fbdev/core/fbmem.c index 9b035ef4d552..265efa189bcc 100644 --- a/drivers/video/fbdev/core/fbmem.c +++ b/drivers/video/fbdev/core/fbmem.c @@ -1789,6 +1789,17 @@ int remove_conflicting_framebuffers(struct apertures_struct *a, if (do_free) kfree(a);
+ /* + * If a driver asked to unregister a platform device registered by + * sysfb, then can be assumed that this is a driver for a display + * that is set up by the system firmware and has a generic driver. + * + * Drivers for devices that don't have a generic driver will never + * ask for this, so let's assume that a real driver for the display + * was already probed and prevent sysfb to register devices later. + */ + sysfb_disable(); + return 0; } EXPORT_SYMBOL(remove_conflicting_framebuffers);
On Wed, May 11, 2022 at 01:31:44PM +0200, Javier Martinez Canillas wrote:
The platform devices registered by sysfb match with firmware-based DRM or fbdev drivers, that are used to have early graphics using a framebuffer provided by the system firmware.
DRM or fbdev drivers later are probed and remove all conflicting framebuffers, leading to these platform devices for generic drivers to be unregistered.
But the current solution has a race, since the sysfb_init() function could be called after a DRM or fbdev driver is probed and request to unregister the devices for drivers with conflicting framebuffes.
To prevent this, disable any future sysfb platform device registration by calling sysfb_disable(), if a driver requests to remove the conflicting framebuffers.
Suggested-by: Daniel Vetter daniel.vetter@ffwll.ch Signed-off-by: Javier Martinez Canillas javierm@redhat.com Reviewed-by: Daniel Vetter daniel.vetter@ffwll.ch
Changes in v5:
- Move the sysfb_disable() call at conflicting framebuffers again to avoid the need of a DRIVER_FIRMWARE capability flag.
- Add Daniel Vetter's Reviewed-by tag again since reverted to the old patch that he already reviewed in v2.
Changes in v3:
- Call sysfb_disable() when a DRM dev and a fbdev are registered rather than when conflicting framebuffers are removed (Thomas Zimmermann).
- Call sysfb_disable() when a fbdev framebuffer is registered rather than when conflicting framebuffers are removed (Thomas Zimmermann).
- Drop Daniel Vetter's Reviewed-by tag since patch changed a lot.
Changes in v2:
- Explain in the commit message that fbmem has to unregister the device as fallback if a driver registered the device itself (Daniel Vetter).
- Also explain that fallback in a comment in the code (Daniel Vetter).
- Don't encode in fbmem the assumption that sysfb will always register platform devices (Daniel Vetter).
- Add a FIXME comment about drivers registering devices (Daniel Vetter).
drivers/video/fbdev/core/fbmem.c | 11 +++++++++++ 1 file changed, 11 insertions(+)
diff --git a/drivers/video/fbdev/core/fbmem.c b/drivers/video/fbdev/core/fbmem.c index 9b035ef4d552..265efa189bcc 100644 --- a/drivers/video/fbdev/core/fbmem.c +++ b/drivers/video/fbdev/core/fbmem.c @@ -1789,6 +1789,17 @@ int remove_conflicting_framebuffers(struct apertures_struct *a, if (do_free) kfree(a);
- /*
* If a driver asked to unregister a platform device registered by* sysfb, then can be assumed that this is a driver for a display* that is set up by the system firmware and has a generic driver.** Drivers for devices that don't have a generic driver will never* ask for this, so let's assume that a real driver for the display* was already probed and prevent sysfb to register devices later.*/- sysfb_disable();
So the og version had (or should have had at least) the sysfb_disable() call before we go through the loop and try to unregister stuff. I think this needs to be done before we call do_remove_conflicting_framebuffer() instead. With that:
Reviewed-by: Daniel Vetter daniel.vetter@ffwll.ch
- return 0;
} EXPORT_SYMBOL(remove_conflicting_framebuffers); -- 2.35.1
Hello Daniel,
On 6/7/22 17:01, Daniel Vetter wrote:
[snip]
drivers/video/fbdev/core/fbmem.c | 11 +++++++++++ 1 file changed, 11 insertions(+)
diff --git a/drivers/video/fbdev/core/fbmem.c b/drivers/video/fbdev/core/fbmem.c index 9b035ef4d552..265efa189bcc 100644 --- a/drivers/video/fbdev/core/fbmem.c +++ b/drivers/video/fbdev/core/fbmem.c @@ -1789,6 +1789,17 @@ int remove_conflicting_framebuffers(struct apertures_struct *a, if (do_free) kfree(a);
- /*
* If a driver asked to unregister a platform device registered by* sysfb, then can be assumed that this is a driver for a display* that is set up by the system firmware and has a generic driver.** Drivers for devices that don't have a generic driver will never* ask for this, so let's assume that a real driver for the display* was already probed and prevent sysfb to register devices later.*/- sysfb_disable();
So the og version had (or should have had at least) the sysfb_disable() call before we go through the loop and try to unregister stuff. I think this needs to be done before we call do_remove_conflicting_framebuffer() instead. With that:
Yes, the original version did that but also the original version didn't attempt to remove the devices registered by sysfb on sysfb_disable().
I was going to answer that this has to be done after the loop because that way fbmem could first ask sysfb to remove the devices, but then I realized that you are correct That this wouldn't be needed if sysfb does the disable (and unregistration) before the loop.
So by doing it before the loop, we should be able to drop [PATCH v5 4/7] fbdev: Make sysfb to unregister its own registered devices:
https://lists.freedesktop.org/archives/dri-devel/2022-May/355201.html
Since by the time the loop is executed, no registered_fb associated with a device that was registered by sysfb should be present in that array.
From: Daniel Vetter daniel.vetter@ffwll.ch
This reverts commit fb561bf9abde49f7e00fdbf9ed2ccf2d86cac8ee.
With
commit 27599aacbaefcbf2af7b06b0029459bbf682000d Author: Thomas Zimmermann tzimmermann@suse.de Date: Tue Jan 25 10:12:18 2022 +0100
fbdev: Hot-unplug firmware fb devices on forced removal
this should be fixed properly and we can remove this somewhat hackish check here (e.g. this won't catch drm drivers if fbdev emulation isn't enabled).
Cc: Thomas Zimmermann tzimmermann@suse.de Cc: Zack Rusin zackr@vmware.com Cc: Javier Martinez Canillas javierm@redhat.com Cc: Zack Rusin zackr@vmware.com Cc: Hans de Goede hdegoede@redhat.com Cc: Ilya Trukhanov lahvuun@gmail.com Signed-off-by: Daniel Vetter daniel.vetter@intel.com Signed-off-by: Daniel Vetter daniel.vetter@ffwll.ch Reviewed-by: Javier Martinez Canillas javierm@redhat.com Cc: Peter Jones pjones@redhat.com Cc: linux-fbdev@vger.kernel.org
Signed-off-by: Javier Martinez Canillas javierm@redhat.com ---
(no changes since v1)
drivers/video/fbdev/efifb.c | 11 ----------- drivers/video/fbdev/simplefb.c | 11 ----------- 2 files changed, 22 deletions(-)
diff --git a/drivers/video/fbdev/efifb.c b/drivers/video/fbdev/efifb.c index ea42ba6445b2..edca3703b964 100644 --- a/drivers/video/fbdev/efifb.c +++ b/drivers/video/fbdev/efifb.c @@ -351,17 +351,6 @@ static int efifb_probe(struct platform_device *dev) char *option = NULL; efi_memory_desc_t md;
- /* - * Generic drivers must not be registered if a framebuffer exists. - * If a native driver was probed, the display hardware was already - * taken and attempting to use the system framebuffer is dangerous. - */ - if (num_registered_fb > 0) { - dev_err(&dev->dev, - "efifb: a framebuffer is already registered\n"); - return -EINVAL; - } - if (screen_info.orig_video_isVGA != VIDEO_TYPE_EFI || pci_dev_disabled) return -ENODEV;
diff --git a/drivers/video/fbdev/simplefb.c b/drivers/video/fbdev/simplefb.c index 94fc9c6d0411..0ef41173325a 100644 --- a/drivers/video/fbdev/simplefb.c +++ b/drivers/video/fbdev/simplefb.c @@ -413,17 +413,6 @@ static int simplefb_probe(struct platform_device *pdev) struct simplefb_par *par; struct resource *res, *mem;
- /* - * Generic drivers must not be registered if a framebuffer exists. - * If a native driver was probed, the display hardware was already - * taken and attempting to use the system framebuffer is dangerous. - */ - if (num_registered_fb > 0) { - dev_err(&pdev->dev, - "simplefb: a framebuffer is already registered\n"); - return -EINVAL; - } - if (fb_get_options("simplefb", NULL)) return -ENODEV;
From: Daniel Vetter daniel.vetter@ffwll.ch
Well except when the olpc dcon fbdev driver is enabled, that thing digs around in there in rather unfixable ways.
Cc oldc_dcon maintainers as fyi.
v2: I typoed the config name (0day)
Cc: kernel test robot lkp@intel.com Cc: Jens Frederich jfrederich@gmail.com Cc: Jon Nettleton jon.nettleton@gmail.com Cc: Greg Kroah-Hartman gregkh@linuxfoundation.org Cc: linux-staging@lists.linux.dev Signed-off-by: Daniel Vetter daniel.vetter@intel.com Signed-off-by: Daniel Vetter daniel.vetter@ffwll.ch Reviewed-by: Javier Martinez Canillas javierm@redhat.com Cc: Daniel Vetter daniel@ffwll.ch Cc: Helge Deller deller@gmx.de Cc: Matthew Wilcox willy@infradead.org Cc: Sam Ravnborg sam@ravnborg.org Cc: Tetsuo Handa penguin-kernel@i-love.sakura.ne.jp Cc: Zhen Lei thunder.leizhen@huawei.com Cc: Alex Deucher alexander.deucher@amd.com Cc: Xiyu Yang xiyuyang19@fudan.edu.cn Cc: linux-fbdev@vger.kernel.org Cc: Zheyu Ma zheyuma97@gmail.com Cc: Guenter Roeck linux@roeck-us.net Signed-off-by: Javier Martinez Canillas javierm@redhat.com ---
(no changes since v1)
drivers/video/fbdev/core/fbmem.c | 8 ++++++-- include/linux/fb.h | 7 +++---- 2 files changed, 9 insertions(+), 6 deletions(-)
diff --git a/drivers/video/fbdev/core/fbmem.c b/drivers/video/fbdev/core/fbmem.c index 265efa189bcc..6cab5f4c1fb3 100644 --- a/drivers/video/fbdev/core/fbmem.c +++ b/drivers/video/fbdev/core/fbmem.c @@ -50,10 +50,14 @@ static DEFINE_MUTEX(registration_lock);
struct fb_info *registered_fb[FB_MAX] __read_mostly; -EXPORT_SYMBOL(registered_fb); - int num_registered_fb __read_mostly; +#if IS_ENABLED(CONFIG_FB_OLPC_DCON) +EXPORT_SYMBOL(registered_fb); EXPORT_SYMBOL(num_registered_fb); +#endif +#define for_each_registered_fb(i) \ + for (i = 0; i < FB_MAX; i++) \ + if (!registered_fb[i]) {} else
bool fb_center_logo __read_mostly;
diff --git a/include/linux/fb.h b/include/linux/fb.h index bbe1e4571899..c563e24b6293 100644 --- a/include/linux/fb.h +++ b/include/linux/fb.h @@ -632,16 +632,15 @@ extern int fb_get_color_depth(struct fb_var_screeninfo *var, extern int fb_get_options(const char *name, char **option); extern int fb_new_modelist(struct fb_info *info);
+#if IS_ENABLED(CONFIG_FB_OLPC_DCON) extern struct fb_info *registered_fb[FB_MAX]; + extern int num_registered_fb; +#endif extern bool fb_center_logo; extern int fb_logo_count; extern struct class *fb_class;
-#define for_each_registered_fb(i) \ - for (i = 0; i < FB_MAX; i++) \ - if (!registered_fb[i]) {} else - static inline void lock_fb_info(struct fb_info *info) { mutex_lock(&info->lock);
Hi Javier.
On Wed, May 11, 2022 at 01:32:30PM +0200, Javier Martinez Canillas wrote:
From: Daniel Vetter daniel.vetter@ffwll.ch
Well except when the olpc dcon fbdev driver is enabled, that thing digs around in there in rather unfixable ways.
Cc oldc_dcon maintainers as fyi.
Another way to fix this is to mark FB_OLPC_DCON and add a TODO entry to fix this. We are really not supposed to carry such special code around to keep staging working.
I know this may not be a popular viewpoint, but just look at the ugly workarounds required here.
Sam
v2: I typoed the config name (0day)
Cc: kernel test robot lkp@intel.com Cc: Jens Frederich jfrederich@gmail.com Cc: Jon Nettleton jon.nettleton@gmail.com Cc: Greg Kroah-Hartman gregkh@linuxfoundation.org Cc: linux-staging@lists.linux.dev Signed-off-by: Daniel Vetter daniel.vetter@intel.com Signed-off-by: Daniel Vetter daniel.vetter@ffwll.ch Reviewed-by: Javier Martinez Canillas javierm@redhat.com Cc: Daniel Vetter daniel@ffwll.ch Cc: Helge Deller deller@gmx.de Cc: Matthew Wilcox willy@infradead.org Cc: Sam Ravnborg sam@ravnborg.org Cc: Tetsuo Handa penguin-kernel@i-love.sakura.ne.jp Cc: Zhen Lei thunder.leizhen@huawei.com Cc: Alex Deucher alexander.deucher@amd.com Cc: Xiyu Yang xiyuyang19@fudan.edu.cn Cc: linux-fbdev@vger.kernel.org Cc: Zheyu Ma zheyuma97@gmail.com Cc: Guenter Roeck linux@roeck-us.net Signed-off-by: Javier Martinez Canillas javierm@redhat.com
(no changes since v1)
drivers/video/fbdev/core/fbmem.c | 8 ++++++-- include/linux/fb.h | 7 +++---- 2 files changed, 9 insertions(+), 6 deletions(-)
diff --git a/drivers/video/fbdev/core/fbmem.c b/drivers/video/fbdev/core/fbmem.c index 265efa189bcc..6cab5f4c1fb3 100644 --- a/drivers/video/fbdev/core/fbmem.c +++ b/drivers/video/fbdev/core/fbmem.c @@ -50,10 +50,14 @@ static DEFINE_MUTEX(registration_lock);
struct fb_info *registered_fb[FB_MAX] __read_mostly; -EXPORT_SYMBOL(registered_fb);
int num_registered_fb __read_mostly; +#if IS_ENABLED(CONFIG_FB_OLPC_DCON) +EXPORT_SYMBOL(registered_fb); EXPORT_SYMBOL(num_registered_fb); +#endif
It is stuff like this I refer to as "ugly" in the comment above.
Sam
On 5/11/22 10:00, Sam Ravnborg wrote:
Hi Javier.
On Wed, May 11, 2022 at 01:32:30PM +0200, Javier Martinez Canillas wrote:
From: Daniel Vetter daniel.vetter@ffwll.ch
Well except when the olpc dcon fbdev driver is enabled, that thing digs around in there in rather unfixable ways.
Cc oldc_dcon maintainers as fyi.
Another way to fix this is to mark FB_OLPC_DCON and add a TODO entry to fix this. We are really not supposed to carry such special code around to keep staging working.
I know this may not be a popular viewpoint, but just look at the ugly workarounds required here.
Sam
v2: I typoed the config name (0day)
Cc: kernel test robot lkp@intel.com Cc: Jens Frederich jfrederich@gmail.com Cc: Jon Nettleton jon.nettleton@gmail.com Cc: Greg Kroah-Hartman gregkh@linuxfoundation.org Cc: linux-staging@lists.linux.dev Signed-off-by: Daniel Vetter daniel.vetter@intel.com Signed-off-by: Daniel Vetter daniel.vetter@ffwll.ch Reviewed-by: Javier Martinez Canillas javierm@redhat.com Cc: Daniel Vetter daniel@ffwll.ch Cc: Helge Deller deller@gmx.de Cc: Matthew Wilcox willy@infradead.org Cc: Sam Ravnborg sam@ravnborg.org Cc: Tetsuo Handa penguin-kernel@i-love.sakura.ne.jp Cc: Zhen Lei thunder.leizhen@huawei.com Cc: Alex Deucher alexander.deucher@amd.com Cc: Xiyu Yang xiyuyang19@fudan.edu.cn Cc: linux-fbdev@vger.kernel.org Cc: Zheyu Ma zheyuma97@gmail.com Cc: Guenter Roeck linux@roeck-us.net Signed-off-by: Javier Martinez Canillas javierm@redhat.com
(no changes since v1)
drivers/video/fbdev/core/fbmem.c | 8 ++++++-- include/linux/fb.h | 7 +++---- 2 files changed, 9 insertions(+), 6 deletions(-)
diff --git a/drivers/video/fbdev/core/fbmem.c b/drivers/video/fbdev/core/fbmem.c index 265efa189bcc..6cab5f4c1fb3 100644 --- a/drivers/video/fbdev/core/fbmem.c +++ b/drivers/video/fbdev/core/fbmem.c @@ -50,10 +50,14 @@ static DEFINE_MUTEX(registration_lock);
struct fb_info *registered_fb[FB_MAX] __read_mostly; -EXPORT_SYMBOL(registered_fb);
- int num_registered_fb __read_mostly;
+#if IS_ENABLED(CONFIG_FB_OLPC_DCON) +EXPORT_SYMBOL(registered_fb); EXPORT_SYMBOL(num_registered_fb); +#endif
It is stuff like this I refer to as "ugly" in the comment above.
My "solution" for that kind of thing is to use a namespace, such as
EXPORT_SYMBOL_NS(registered_fb, FB_OLPC_DCON); EXPORT_SYMBOL_NS(num_registered_fb, FB_OLPC_DCON);
and import it from the offending code. That avoids ifdefs while at the same time limiting the use of the symbols to the expected scope. Of course that could be abused but that abuse would be obvious.
Guenter
Hello Guenter,
On 5/11/22 19:17, Guenter Roeck wrote:
On 5/11/22 10:00, Sam Ravnborg wrote:
[snip]
struct fb_info *registered_fb[FB_MAX] __read_mostly; -EXPORT_SYMBOL(registered_fb);
- int num_registered_fb __read_mostly;
+#if IS_ENABLED(CONFIG_FB_OLPC_DCON) +EXPORT_SYMBOL(registered_fb); EXPORT_SYMBOL(num_registered_fb); +#endif
It is stuff like this I refer to as "ugly" in the comment above.
My "solution" for that kind of thing is to use a namespace, such as
EXPORT_SYMBOL_NS(registered_fb, FB_OLPC_DCON); EXPORT_SYMBOL_NS(num_registered_fb, FB_OLPC_DCON);
Using a namespace in this case is indeed a great idea I think.
I've used in the past to limit the export of a symbol for within a driver that could be scattered across different compilations units, but it never occurred to me using it to limit symbols exported by core code.
and import it from the offending code. That avoids ifdefs while at the same time limiting the use of the symbols to the expected scope. Of course that could be abused but that abuse would be obvious.
Agreed. For the next revision, besides using an namespaced export symbol as you suggested, I'll include a comment to make clear that it shouldn't by any other driver and FB_OLPC_DCON fixed instead.
On Wed, May 11, 2022 at 07:34:38PM +0200, Javier Martinez Canillas wrote:
Hello Guenter,
On 5/11/22 19:17, Guenter Roeck wrote:
On 5/11/22 10:00, Sam Ravnborg wrote:
[snip]
struct fb_info *registered_fb[FB_MAX] __read_mostly; -EXPORT_SYMBOL(registered_fb);
- int num_registered_fb __read_mostly;
+#if IS_ENABLED(CONFIG_FB_OLPC_DCON) +EXPORT_SYMBOL(registered_fb); EXPORT_SYMBOL(num_registered_fb); +#endif
It is stuff like this I refer to as "ugly" in the comment above.
My "solution" for that kind of thing is to use a namespace, such as
EXPORT_SYMBOL_NS(registered_fb, FB_OLPC_DCON); EXPORT_SYMBOL_NS(num_registered_fb, FB_OLPC_DCON);
Using a namespace in this case is indeed a great idea I think.
I've used in the past to limit the export of a symbol for within a driver that could be scattered across different compilations units, but it never occurred to me using it to limit symbols exported by core code.
and import it from the offending code. That avoids ifdefs while at the same time limiting the use of the symbols to the expected scope. Of course that could be abused but that abuse would be obvious.
Agreed. For the next revision, besides using an namespaced export symbol as you suggested, I'll include a comment to make clear that it shouldn't by any other driver and FB_OLPC_DCON fixed instead.
A very nice compromise, thanks Guenter and Javier.
Sam
Hi Javier,
thanks again for providing the examples. I think I now better get what you're trying to solve.
First of all let's merge patch 3, as it seems unrelated.
For the other patches, I'd like to take a step back and try to solve the broader problem. IIRC we talked about this briefly already.
From my understanding, the problem of the current code is that removal of the firmware device is build around drivers (either DRM or fbdev). Everything works fine if a driver is bound to the firmware device and the native driver can remove it. In other case, we have to manually disable sysfb and force-remove unbound firmware devices. And the patchset doesn't even cover firmware devices that come from DT nodes.
But what we really want is to track resource ownership based on devices. When we add a firmware device (via sysfb or DT), we immediately add it to a list of firmware devices. When the native driver arrives, it can remove the firmware device even if no driver has been bound.
We can also operate in the other way if the native drivers implicitly reserves the framebuffer range. If sysfb would try to register a firmware device in that range, he can let it fail. No more need to fully disable sysfb on the first arriving native device.
We already track the memory ranges in drm aperture helpers. We'd need to move the code to a more prominent location (e.g., <linux/aperture.h>) and change fbdev to use it. Sysfb and DT code needs to insert platform devices upon creation. We can then implement the more fancy stuff, such as tracking native-device memory. (And if we ever get to fix all usage of Linux' request-mem-region, we can even move all the functionality there).
Best regards Thomas
Am 11.05.22 um 13:24 schrieb Javier Martinez Canillas:
Hello,
The patches in this series contain mostly changes suggested by Daniel Vetter Thomas Zimmermann. They aim to fix existing races between the Generic System Framebuffer (sysfb) infrastructure and the fbdev and DRM device registration.
For example, it is currently possible for sysfb to register a platform device after a real DRM driver was registered and requested to remove the conflicting framebuffers. Or is possible for a simple{fb,drm} to match with a device previously registered by sysfb, even after a real driver is present.
A symptom of this issue, was worked around with the commit fb561bf9abde ("fbdev: Prevent probing generic drivers if a FB is already registered") but that's really a hack and should be reverted instead.
This series attempt to fix it more correctly and revert the mentioned hack. That will also allow to make the num_registered_fb variable not visible to drivers anymore, since that's internal to fbdev core.
Pach 1 is just a simple cleanup in preparation for later patches.
Patch 2 add a sysfb_disable() and sysfb_try_unregister() helpers to allow disabling sysfb and attempt to unregister registered devices respectively.
Patch 3 changes how is dealt with conflicting framebuffers unregistering, rather than having a variable to determine if a lock should be take, it just drops the lock before unregistering the platform device.
Patch 4 changes the fbdev core to not attempt to unregister devices that were registered by sysfb, let the same code doing the registration to also handle the unregistration.
Patch 5 fixes the race that exists between sysfb devices registration and fbdev framebuffer devices registration, by disabling the sysfb when a DRM or fbdev driver requests to remove conflicting framebuffers.
Patch 6 is the revert patch that was posted by Daniel before but dropped from his set and finally patch 7 is the one that makes num_registered_fb private to fbmem.c, to not allow drivers to use it anymore.
The patches were tested on a rpi4 with the vc4, simpledrm and simplefb drivers, using different combinations of built-in and as a module.
For example, having simpledrm as a module and loading it after the vc4 driver probed would not register a DRM device, which happens now without the patches from this series.
Best regards, Javier
Changes in v5:
- Move the sysfb_disable() call at conflicting framebuffers again to avoid the need of a DRIVER_FIRMWARE capability flag.
- Add Daniel Vetter's Reviewed-by tag again since reverted to the old patch that he already reviewed in v2.
- Drop patches that added a DRM_FIRMWARE capability and use them since the case those prevented could be ignored (Daniel Vetter).
Changes in v4:
- Make sysfb_disable() to also attempt to unregister a device.
- Drop call to sysfb_disable() in fbmem since is done in other places now.
- Add patch to make registered_fb[] private.
- Add patches that introduce the DRM_FIRMWARE capability and usage.
Changes in v3:
- Add Thomas Zimmermann's Reviewed-by tag to patch #1.
- Call sysfb_disable() when a DRM dev and a fbdev are registered rather than when conflicting framebuffers are removed (Thomas Zimmermann).
- Call sysfb_disable() when a fbdev framebuffer is registered rather than when conflicting framebuffers are removed (Thomas Zimmermann).
- Drop Daniel Vetter's Reviewed-by tag since patch changed a lot.
- Rebase on top of latest drm-misc-next branch.
Changes in v2:
- Rebase on top of latest drm-misc-next and fix conflicts (Daniel Vetter).
- Add kernel-doc comments and include in other_interfaces.rst (Daniel Vetter).
- Explain in the commit message that fbmem has to unregister the device as fallback if a driver registered the device itself (Daniel Vetter).
- Also explain that fallback in a comment in the code (Daniel Vetter).
- Don't encode in fbmem the assumption that sysfb will always register platform devices (Daniel Vetter).
- Add a FIXME comment about drivers registering devices (Daniel Vetter).
- Explain in the commit message that fbmem has to unregister the device as fallback if a driver registered the device itself (Daniel Vetter).
- Also explain that fallback in a comment in the code (Daniel Vetter).
- Don't encode in fbmem the assumption that sysfb will always register platform devices (Daniel Vetter).
- Add a FIXME comment about drivers registering devices (Daniel Vetter).
- Drop RFC prefix since patches were already reviewed by Daniel Vetter.
- Add Daniel Reviewed-by tags to the patches.
Daniel Vetter (2): Revert "fbdev: Prevent probing generic drivers if a FB is already registered" fbdev: Make registered_fb[] private to fbmem.c
Javier Martinez Canillas (5): firmware: sysfb: Make sysfb_create_simplefb() return a pdev pointer firmware: sysfb: Add helpers to unregister a pdev and disable registration fbdev: Restart conflicting fb removal loop when unregistering devices fbdev: Make sysfb to unregister its own registered devices fbdev: Disable sysfb device registration when removing conflicting FBs
.../driver-api/firmware/other_interfaces.rst | 6 ++ drivers/firmware/sysfb.c | 91 +++++++++++++++++-- drivers/firmware/sysfb_simplefb.c | 16 ++-- drivers/video/fbdev/core/fbmem.c | 67 +++++++++++--- drivers/video/fbdev/efifb.c | 11 --- drivers/video/fbdev/simplefb.c | 11 --- include/linux/fb.h | 8 +- include/linux/sysfb.h | 29 +++++- 8 files changed, 178 insertions(+), 61 deletions(-)
Hello Thomas,
Thanks for your feedback and comments.
On 5/13/22 12:48, Thomas Zimmermann wrote:
Hi Javier,
thanks again for providing the examples. I think I now better get what you're trying to solve.
You are welcome.
First of all let's merge patch 3, as it seems unrelated.
Agreed. I can push it to drm-misc-next.
For the other patches, I'd like to take a step back and try to solve the broader problem. IIRC we talked about this briefly already.
Yes, that's what we discussed on IRC some time ago.
From my understanding, the problem of the current code is that removal of the firmware device is build around drivers (either DRM or fbdev). Everything works fine if a driver is bound to the firmware device and the native driver can remove it. In other case, we have to manually
And this is the common case, since most kernels will have some driver that binds to a platform device registered to provide the firmware FB.
disable sysfb and force-remove unbound firmware devices. And the patchset doesn't even cover firmware devices that come from DT nodes.
Indeed.
But what we really want is to track resource ownership based on devices. When we add a firmware device (via sysfb or DT), we immediately add it to a list of firmware devices. When the native driver arrives, it can remove the firmware device even if no driver has been bound.
We can also operate in the other way if the native drivers implicitly reserves the framebuffer range. If sysfb would try to register a firmware device in that range, he can let it fail. No more need to fully disable sysfb on the first arriving native device.
We already track the memory ranges in drm aperture helpers. We'd need to move the code to a more prominent location (e.g., <linux/aperture.h>) and change fbdev to use it. Sysfb and DT code needs to insert platform devices upon creation. We can then implement the more fancy stuff, such as tracking native-device memory. (And if we ever get to fix all usage of Linux' request-mem-region, we can even move all the functionality there).
Agreed. And as mentioned, the race that these patches attempt to fix are for the less common case when a native driver probes but either no generic driver registered a framebuffer yet or the platform device wasn't registered yet.
But this can only happen if for example a native driver is built-in but the generic driver is build as a module, which is not the common configuration.
What most distros do is the opposite, to have {simple,of,efi,vesa}fb or simpledrm built-in and the native drivers built as modules.
So there's no rush to fix this by piling more hacks on top of the ones we already have and instead try to fix it more properly as you suggested.
Hi Javier
Am 13.05.22 um 13:10 schrieb Javier Martinez Canillas: ...
We already track the memory ranges in drm aperture helpers. We'd need to move the code to a more prominent location (e.g., <linux/aperture.h>) and change fbdev to use it. Sysfb and DT code needs to insert platform devices upon creation. We can then implement the more fancy stuff, such as tracking native-device memory. (And if we ever get to fix all usage of Linux' request-mem-region, we can even move all the functionality there).
Agreed. And as mentioned, the race that these patches attempt to fix are for the less common case when a native driver probes but either no generic driver registered a framebuffer yet or the platform device wasn't registered yet.
But this can only happen if for example a native driver is built-in but the generic driver is build as a module, which is not the common configuration.
What most distros do is the opposite, to have {simple,of,efi,vesa}fb or simpledrm built-in and the native drivers built as modules.
So there's no rush to fix this by piling more hacks on top of the ones we already have and instead try to fix it more properly as you suggested.
A first step would be to use DRM's aperture helpers in fbdev. That would be a good idea anyway, as it would simplify both. You already mentioned some API changes to make aperture helpers DRM-independent.
The affected fbdev drivers use platform devices, so this should be easy.
Aperture helpers have something like the registration_lock. [1] I don't know if we need to recreate patch 3 for this as well.
If we absolutely need some special detachment handling for fbdev, we can make devm_aperture_aquire() a public interface. The detach helper is provided by the caller.
Best regards Thomas
[1] https://elixir.bootlin.com/linux/v5.17.6/source/drivers/gpu/drm/drm_aperture... [2] https://elixir.bootlin.com/linux/v5.17.6/source/drivers/gpu/drm/drm_aperture...
dri-devel@lists.freedesktop.org
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Daniel Vetter -
Guenter Roeck -
Javier Martinez Canillas -
Sam Ravnborg -
Thomas Zimmermann