The simpledrm driver allows to use the frame buffer that was set-up by the firmware. This gives early video output before the platform DRM driver is probed and takes over.
But it would be useful to have a way to disable this take over by the real DRM drivers. For example, there may be bugs in the DRM drivers that could cause the display output to not work correctly.
For those cases, it would be good to keep the simpledrm driver instead and at least get a working display as set-up by the firmware.
Let's add a drm.remove_fb boolean kernel command line parameter, that when set to false will prevent the conflicting framebuffers to being removed.
Since the drivers call drm_aperture_remove_conflicting_framebuffers() very early in their probe callback, this will cause the drivers' probe to fail.
Thanks to Neal Gompa for the suggestion and Thomas Zimmermann for the idea on how this could be implemented.
Suggested-by: Neal Gompa ngompa13@gmail.com Signed-off-by: Javier Martinez Canillas javierm@redhat.com --- Hello,
I'm sending this as an RFC because I wasn't sure about the correct name for this module parameter, and also if 'remove_fb=0' is intitutive or instead a parameter that's enabled is preferred (i.e: 'disable_fb_removal=1').
Best regards, Javier
drivers/gpu/drm/drm_aperture.c | 19 +++++++++++++++++++ 1 file changed, 19 insertions(+)
diff --git a/drivers/gpu/drm/drm_aperture.c b/drivers/gpu/drm/drm_aperture.c index 74bd4a76b253..0b454c8f7465 100644 --- a/drivers/gpu/drm/drm_aperture.c +++ b/drivers/gpu/drm/drm_aperture.c @@ -14,6 +14,11 @@ #include <drm/drm_drv.h> #include <drm/drm_print.h>
+static bool drm_aperture_remove_fb = true; +module_param_named(remove_fb, drm_aperture_remove_fb, bool, 0600); +MODULE_PARM_DESC(remove_fb, + "Allow conflicting framebuffers removal [default=true]"); + /** * DOC: overview * @@ -283,6 +288,9 @@ static void drm_aperture_detach_drivers(resource_size_t base, resource_size_t si * This function removes graphics device drivers which use memory range described by * @base and @size. * + * The conflicting framebuffers removal can be disabled by setting the drm.remove_fb=0 kernel + * command line option. When this is disabled, the function will return an -EINVAL errno code. + * * Returns: * 0 on success, or a negative errno code otherwise */ @@ -292,7 +300,12 @@ int drm_aperture_remove_conflicting_framebuffers(resource_size_t base, resource_ #if IS_REACHABLE(CONFIG_FB) struct apertures_struct *a; int ret; +#endif + + if (!drm_aperture_remove_fb) + return -EINVAL;
+#if IS_REACHABLE(CONFIG_FB) a = alloc_apertures(1); if (!a) return -ENOMEM; @@ -322,6 +335,9 @@ EXPORT_SYMBOL(drm_aperture_remove_conflicting_framebuffers); * for any of @pdev's memory bars. The function assumes that PCI device with * shadowed ROM drives a primary display and so kicks out vga16fb. * + * The conflicting framebuffers removal can be disabled by setting the drm.remove_fb=0 kernel + * command line option. When this is disabled, the function will return an -EINVAL errno code. + * * Returns: * 0 on success, or a negative errno code otherwise */ @@ -331,6 +347,9 @@ int drm_aperture_remove_conflicting_pci_framebuffers(struct pci_dev *pdev, resource_size_t base, size; int bar, ret = 0;
+ if (!drm_aperture_remove_fb) + return -EINVAL; + for (bar = 0; bar < PCI_STD_NUM_BARS; ++bar) { if (!(pci_resource_flags(pdev, bar) & IORESOURCE_MEM)) continue;
On Fri, Oct 22, 2021 at 10:40 AM Javier Martinez Canillas javierm@redhat.com wrote:
The simpledrm driver allows to use the frame buffer that was set-up by the firmware. This gives early video output before the platform DRM driver is probed and takes over.
But it would be useful to have a way to disable this take over by the real DRM drivers. For example, there may be bugs in the DRM drivers that could cause the display output to not work correctly.
For those cases, it would be good to keep the simpledrm driver instead and at least get a working display as set-up by the firmware.
Let's add a drm.remove_fb boolean kernel command line parameter, that when set to false will prevent the conflicting framebuffers to being removed.
Since the drivers call drm_aperture_remove_conflicting_framebuffers() very early in their probe callback, this will cause the drivers' probe to fail.
Thanks to Neal Gompa for the suggestion and Thomas Zimmermann for the idea on how this could be implemented.
Suggested-by: Neal Gompa ngompa13@gmail.com Signed-off-by: Javier Martinez Canillas javierm@redhat.com
Hello,
I'm sending this as an RFC because I wasn't sure about the correct name for this module parameter, and also if 'remove_fb=0' is intitutive or instead a parameter that's enabled is preferred (i.e: 'disable_fb_removal=1').
In general, I think the patch is fine, but it might make sense to name the parameter after the *effect* rather than the *action*. That is, the effect of this option is that we don't probe and hand over to a more appropriate hardware DRM driver.
Since the effect (in DRM terms) is that we don't use platform DRM modules, perhaps we could name the option one of these:
* drm.noplatformdrv * drm.simpledrv * drm.force_simple
I'm inclined to say we should use the drm.* namespace for the cmdline option because that makes it clear what subsystem it affects. The legacy "nomodeset" option kind of sucked because it didn't really tell you what that meant, and I'd rather not repeat that mistake.
-- 真実はいつも一つ！/ Always, there's only one truth!
Hello Neal,
Thanks for your feedback.
On 10/22/21 16:56, Neal Gompa wrote:
On Fri, Oct 22, 2021 at 10:40 AM Javier Martinez Canillas javierm@redhat.com wrote:
The simpledrm driver allows to use the frame buffer that was set-up by the firmware. This gives early video output before the platform DRM driver is probed and takes over.
But it would be useful to have a way to disable this take over by the real DRM drivers. For example, there may be bugs in the DRM drivers that could cause the display output to not work correctly.
For those cases, it would be good to keep the simpledrm driver instead and at least get a working display as set-up by the firmware.
Let's add a drm.remove_fb boolean kernel command line parameter, that when set to false will prevent the conflicting framebuffers to being removed.
Since the drivers call drm_aperture_remove_conflicting_framebuffers() very early in their probe callback, this will cause the drivers' probe to fail.
Thanks to Neal Gompa for the suggestion and Thomas Zimmermann for the idea on how this could be implemented.
Suggested-by: Neal Gompa ngompa13@gmail.com Signed-off-by: Javier Martinez Canillas javierm@redhat.com
Hello,
I'm sending this as an RFC because I wasn't sure about the correct name for this module parameter, and also if 'remove_fb=0' is intitutive or instead a parameter that's enabled is preferred (i.e: 'disable_fb_removal=1').
In general, I think the patch is fine, but it might make sense to name the parameter after the *effect* rather than the *action*. That is, the effect of this option is that we don't probe and hand over to a more appropriate hardware DRM driver.
Since the effect (in DRM terms) is that we don't use platform DRM modules, perhaps we could name the option one of these:
- drm.noplatformdrv
- drm.simpledrv
- drm.force_simple
or maybe drm.disable_handover ? Naming is hard...
I'm inclined to say we should use the drm.* namespace for the cmdline option because that makes it clear what subsystem it affects. The legacy "nomodeset" option kind of sucked because it didn't really tell you what that meant, and I'd rather not repeat that mistake.
Yes, agreed. In fact, that is the case for this patch since the param is in the drm module. I just forgot to mention the namespace in the last paragraph of the comment.
Best regards, -- Javier Martinez Canillas Linux Engineering Red Hat
On Fri, Oct 22, 2021 at 11:16 AM Javier Martinez Canillas javierm@redhat.com wrote:
Hello Neal,
Thanks for your feedback.
On 10/22/21 16:56, Neal Gompa wrote:
On Fri, Oct 22, 2021 at 10:40 AM Javier Martinez Canillas javierm@redhat.com wrote:
The simpledrm driver allows to use the frame buffer that was set-up by the firmware. This gives early video output before the platform DRM driver is probed and takes over.
But it would be useful to have a way to disable this take over by the real DRM drivers. For example, there may be bugs in the DRM drivers that could cause the display output to not work correctly.
For those cases, it would be good to keep the simpledrm driver instead and at least get a working display as set-up by the firmware.
Let's add a drm.remove_fb boolean kernel command line parameter, that when set to false will prevent the conflicting framebuffers to being removed.
Since the drivers call drm_aperture_remove_conflicting_framebuffers() very early in their probe callback, this will cause the drivers' probe to fail.
Thanks to Neal Gompa for the suggestion and Thomas Zimmermann for the idea on how this could be implemented.
Suggested-by: Neal Gompa ngompa13@gmail.com Signed-off-by: Javier Martinez Canillas javierm@redhat.com
Hello,
I'm sending this as an RFC because I wasn't sure about the correct name for this module parameter, and also if 'remove_fb=0' is intitutive or instead a parameter that's enabled is preferred (i.e: 'disable_fb_removal=1').
In general, I think the patch is fine, but it might make sense to name the parameter after the *effect* rather than the *action*. That is, the effect of this option is that we don't probe and hand over to a more appropriate hardware DRM driver.
Since the effect (in DRM terms) is that we don't use platform DRM modules, perhaps we could name the option one of these:
- drm.noplatformdrv
- drm.simpledrv
- drm.force_simple
or maybe drm.disable_handover ? Naming is hard...
That would make sense for a parameter named by the action. If we want to go that route, then I'd be fine with that. My goal is to have something people understand.
I'm inclined to say we should use the drm.* namespace for the cmdline option because that makes it clear what subsystem it affects. The legacy "nomodeset" option kind of sucked because it didn't really tell you what that meant, and I'd rather not repeat that mistake.
Yes, agreed. In fact, that is the case for this patch since the param is in the drm module. I just forgot to mention the namespace in the last paragraph of the comment.
Good to know. :)
-- 真実はいつも一つ！/ Always, there's only one truth!
Hi,
thanks for sending the patch out quickly.
Am 22.10.21 um 16:40 schrieb Javier Martinez Canillas:
The simpledrm driver allows to use the frame buffer that was set-up by the firmware. This gives early video output before the platform DRM driver is probed and takes over.
But it would be useful to have a way to disable this take over by the real DRM drivers. For example, there may be bugs in the DRM drivers that could cause the display output to not work correctly.
For those cases, it would be good to keep the simpledrm driver instead and at least get a working display as set-up by the firmware.
Let's add a drm.remove_fb boolean kernel command line parameter, that when set to false will prevent the conflicting framebuffers to being removed.
Since the drivers call drm_aperture_remove_conflicting_framebuffers() very early in their probe callback, this will cause the drivers' probe to fail.
Thanks to Neal Gompa for the suggestion and Thomas Zimmermann for the idea on how this could be implemented.
Suggested-by: Neal Gompa ngompa13@gmail.com Signed-off-by: Javier Martinez Canillas javierm@redhat.com
Hello,
I'm sending this as an RFC because I wasn't sure about the correct name for this module parameter, and also if 'remove_fb=0' is intitutive or instead a parameter that's enabled is preferred (i.e: 'disable_fb_removal=1').
Best regards, Javier
drivers/gpu/drm/drm_aperture.c | 19 +++++++++++++++++++ 1 file changed, 19 insertions(+)
diff --git a/drivers/gpu/drm/drm_aperture.c b/drivers/gpu/drm/drm_aperture.c index 74bd4a76b253..0b454c8f7465 100644 --- a/drivers/gpu/drm/drm_aperture.c +++ b/drivers/gpu/drm/drm_aperture.c @@ -14,6 +14,11 @@ #include <drm/drm_drv.h> #include <drm/drm_print.h>
+static bool drm_aperture_remove_fb = true;
Global variables should default to zero if somehow possible. This way, they can all be stored in the BSS segment and backed by a single shared zero-filled page. Otherwise they require actual memory. In the worst case, you'd allocate a full page to hold a single boolean.
+module_param_named(remove_fb, drm_aperture_remove_fb, bool, 0600); +MODULE_PARM_DESC(remove_fb,
"Allow conflicting framebuffers removal [default=true]");
And with variables set to zero, a command-line parameter enables non-default behavior (i.e., "drm-param=1"). That more logical than the other way around IMHO.
/**
- DOC: overview
@@ -283,6 +288,9 @@ static void drm_aperture_detach_drivers(resource_size_t base, resource_size_t si
- This function removes graphics device drivers which use memory range described by
- @base and @size.
- The conflicting framebuffers removal can be disabled by setting the drm.remove_fb=0 kernel
- command line option. When this is disabled, the function will return an -EINVAL errno code.
Please use -EBUSY for the error. That's what the acquire function returns in case of a conflict.
*/
- Returns:
- 0 on success, or a negative errno code otherwise
@@ -292,7 +300,12 @@ int drm_aperture_remove_conflicting_framebuffers(resource_size_t base, resource_ #if IS_REACHABLE(CONFIG_FB)
Rather not split up this block. It's better style to put the fbdev-related code into a helper and call it unconditionally.
static drm_aperture_remove_conflicting_fbdev_framebuffers() { #if (FB) ... #endif return 0; }
struct apertures_struct *a; int ret; +#endif
- if (!drm_aperture_remove_fb)
return -EINVAL;
There's still the question of the semantics of this parameter. It's a bit fuzzy.
If you use 'disable_handover' (as you mentioned in another mail), it would mean that only the handover itself is disabled. So if simpledrm is not bound to the device, then a native driver should load. That would be hard to implement with the current code base, where we have to take old fbdev drivers into account.
(And to be pedantic, we don't really do a handover of the device. We hot-unplug the generic platform device, so that the driver for the native device can operate the HW without interference.)
Simpledrm only acquires an aperture, but never removes a driver. If there is a driver already, simpledrm would fail. Only native drivers try to remove drivers and would trigger the test. So your patch is more something like 'disable_native_drivers'.
I'd go with 'disable_native_drivers', or maybe 'disable_device_handover' as a second option. If simpledrm, or any other generic DRM driver, would ever try to remove an existing driver from a device, we'd have to distinguish between native and generic drivers. But that's a trivial problem for later.
+#if IS_REACHABLE(CONFIG_FB) a = alloc_apertures(1); if (!a) return -ENOMEM; @@ -322,6 +335,9 @@ EXPORT_SYMBOL(drm_aperture_remove_conflicting_framebuffers);
- for any of @pdev's memory bars. The function assumes that PCI device with
- shadowed ROM drives a primary display and so kicks out vga16fb.
- The conflicting framebuffers removal can be disabled by setting the drm.remove_fb=0 kernel
- command line option. When this is disabled, the function will return an -EINVAL errno code.
*/
- Returns:
- 0 on success, or a negative errno code otherwise
@@ -331,6 +347,9 @@ int drm_aperture_remove_conflicting_pci_framebuffers(struct pci_dev *pdev, resource_size_t base, size; int bar, ret = 0;
- if (!drm_aperture_remove_fb)
return -EINVAL;
-EBUSY again
Best regards Thomas
- for (bar = 0; bar < PCI_STD_NUM_BARS; ++bar) { if (!(pci_resource_flags(pdev, bar) & IORESOURCE_MEM)) continue;
Hello Thomas,
Thanks a lot for your feedback.
On 10/22/21 21:05, Thomas Zimmermann wrote:
[snip]
+static bool drm_aperture_remove_fb = true;
Global variables should default to zero if somehow possible. This way, they can all be stored in the BSS segment and backed by a single shared zero-filled page. Otherwise they require actual memory. In the worst case, you'd allocate a full page to hold a single boolean.
+module_param_named(remove_fb, drm_aperture_remove_fb, bool, 0600); +MODULE_PARM_DESC(remove_fb,
"Allow conflicting framebuffers removal [default=true]");And with variables set to zero, a command-line parameter enables non-default behavior (i.e., "drm-param=1"). That more logical than the other way around IMHO.
Agreed. I'll change that.
/**
- DOC: overview
@@ -283,6 +288,9 @@ static void drm_aperture_detach_drivers(resource_size_t base, resource_size_t si
- This function removes graphics device drivers which use memory range described by
- @base and @size.
- The conflicting framebuffers removal can be disabled by setting the drm.remove_fb=0 kernel
- command line option. When this is disabled, the function will return an -EINVAL errno code.
Please use -EBUSY for the error. That's what the acquire function returns in case of a conflict.
Sure, makes sense. I was pondering between -EINVAL, -EBUSY and -EPERM.
*/
- Returns:
- 0 on success, or a negative errno code otherwise
@@ -292,7 +300,12 @@ int drm_aperture_remove_conflicting_framebuffers(resource_size_t base, resource_ #if IS_REACHABLE(CONFIG_FB)
Rather not split up this block. It's better style to put the fbdev-related code into a helper and call it unconditionally.
static drm_aperture_remove_conflicting_fbdev_framebuffers() { #if (FB) ... #endif return 0; }
Ok.
struct apertures_struct *a; int ret; +#endif
- if (!drm_aperture_remove_fb)
return -EINVAL;There's still the question of the semantics of this parameter. It's a bit fuzzy.
If you use 'disable_handover' (as you mentioned in another mail), it would mean that only the handover itself is disabled. So if simpledrm is not bound to the device, then a native driver should load. That would be hard to implement with the current code base, where we have to take old fbdev drivers into account.
(And to be pedantic, we don't really do a handover of the device. We hot-unplug the generic platform device, so that the driver for the native device can operate the HW without interference.)
Simpledrm only acquires an aperture, but never removes a driver. If there is a driver already, simpledrm would fail. Only native drivers try > to remove drivers and would trigger the test. So your patch is more something like 'disable_native_drivers'.
I'd go with 'disable_native_drivers', or maybe 'disable_device_handover'
That works for me and "drm.disable_native_drivers" is also what Neal meant with his "drm.noplatformdrv", but yours is much easier to remember / type.
Best regards,
On Sun, Oct 24, 2021 at 4:40 PM Javier Martinez Canillas javierm@redhat.com wrote:
Hello Thomas,
Thanks a lot for your feedback.
On 10/22/21 21:05, Thomas Zimmermann wrote:
There's still the question of the semantics of this parameter. It's a bit fuzzy.
If you use 'disable_handover' (as you mentioned in another mail), it would mean that only the handover itself is disabled. So if simpledrm is not bound to the device, then a native driver should load. That would be hard to implement with the current code base, where we have to take old fbdev drivers into account.
(And to be pedantic, we don't really do a handover of the device. We hot-unplug the generic platform device, so that the driver for the native device can operate the HW without interference.)
Simpledrm only acquires an aperture, but never removes a driver. If there is a driver already, simpledrm would fail. Only native drivers try > to remove drivers and would trigger the test. So your patch is more something like 'disable_native_drivers'.
I'd go with 'disable_native_drivers', or maybe 'disable_device_handover'
That works for me and "drm.disable_native_drivers" is also what Neal meant with his "drm.noplatformdrv", but yours is much easier to remember / type.
I'm good with that too. :)
On Fri, Oct 22, 2021 at 04:40:40PM +0200, Javier Martinez Canillas wrote:
The simpledrm driver allows to use the frame buffer that was set-up by the firmware. This gives early video output before the platform DRM driver is probed and takes over.
But it would be useful to have a way to disable this take over by the real DRM drivers. For example, there may be bugs in the DRM drivers that could cause the display output to not work correctly.
For those cases, it would be good to keep the simpledrm driver instead and at least get a working display as set-up by the firmware.
Let's add a drm.remove_fb boolean kernel command line parameter, that when set to false will prevent the conflicting framebuffers to being removed.
Since the drivers call drm_aperture_remove_conflicting_framebuffers() very early in their probe callback, this will cause the drivers' probe to fail.
Why is that better than just modprobe.blacklisting those drivers?
Hello Ville,
On 10/22/21 21:12, Ville Syrjälä wrote:
On Fri, Oct 22, 2021 at 04:40:40PM +0200, Javier Martinez Canillas wrote:
The simpledrm driver allows to use the frame buffer that was set-up by the firmware. This gives early video output before the platform DRM driver is probed and takes over.
But it would be useful to have a way to disable this take over by the real DRM drivers. For example, there may be bugs in the DRM drivers that could cause the display output to not work correctly.
For those cases, it would be good to keep the simpledrm driver instead and at least get a working display as set-up by the firmware.
Let's add a drm.remove_fb boolean kernel command line parameter, that when set to false will prevent the conflicting framebuffers to being removed.
Since the drivers call drm_aperture_remove_conflicting_framebuffers() very early in their probe callback, this will cause the drivers' probe to fail.
Why is that better than just modprobe.blacklisting those drivers?
Because would allow to deny list all native (as Thomas called it) DRM drivers and only allow the simpledrm driver to be probed. This is useful for distros, since could add a "Basic graphics mode" to the boot menu entries, that could boot the kernel passing a "drm.disable_native_drivers=1" cmdline option.
That way, if there's any problem with a given DRM driver, the distro may be installed and booted using the simpledrm driver and troubleshoot why a native DRM driver is not working. Or try updating the kernel package, etc.
Currently what most distros do is to pass "nomodeset" in this mode. But now that we have the simpledrm driver, would be nice to just use the frame buffer set by the system firmware in those cases.
Best regards,
On 2021-10-24 22:32, Javier Martinez Canillas wrote:
Hello Ville,
On 10/22/21 21:12, Ville Syrjälä wrote:
On Fri, Oct 22, 2021 at 04:40:40PM +0200, Javier Martinez Canillas wrote:
The simpledrm driver allows to use the frame buffer that was set-up by the firmware. This gives early video output before the platform DRM driver is probed and takes over.
But it would be useful to have a way to disable this take over by the real DRM drivers. For example, there may be bugs in the DRM drivers that could cause the display output to not work correctly.
For those cases, it would be good to keep the simpledrm driver instead and at least get a working display as set-up by the firmware.
Let's add a drm.remove_fb boolean kernel command line parameter, that when set to false will prevent the conflicting framebuffers to being removed.
Since the drivers call drm_aperture_remove_conflicting_framebuffers() very early in their probe callback, this will cause the drivers' probe to fail.
Why is that better than just modprobe.blacklisting those drivers?
Because would allow to deny list all native (as Thomas called it) DRM drivers and only allow the simpledrm driver to be probed. This is useful for distros, since could add a "Basic graphics mode" to the boot menu entries, that could boot the kernel passing a "drm.disable_native_drivers=1" cmdline option.
That way, if there's any problem with a given DRM driver, the distro may be installed and booted using the simpledrm driver and troubleshoot why a native DRM driver is not working. Or try updating the kernel package, etc.
For troubleshooting, it'll be helpful if this new parameter can be enabled for the boot via the kernel command line, then disabled again after boot-up. One simple possibility for this would be allowing the parameter to be changed via /sys/module/drm/parameters/<name>, which I suspect doesn't work with the patch as is (due to the 0600 permissions).
Hello Michel,
On 10/25/21 12:45, Michel Dänzer wrote:
On 2021-10-24 22:32, Javier Martinez Canillas wrote:
Hello Ville,
On 10/22/21 21:12, Ville Syrjälä wrote:
On Fri, Oct 22, 2021 at 04:40:40PM +0200, Javier Martinez Canillas wrote:
The simpledrm driver allows to use the frame buffer that was set-up by the firmware. This gives early video output before the platform DRM driver is probed and takes over.
But it would be useful to have a way to disable this take over by the real DRM drivers. For example, there may be bugs in the DRM drivers that could cause the display output to not work correctly.
For those cases, it would be good to keep the simpledrm driver instead and at least get a working display as set-up by the firmware.
Let's add a drm.remove_fb boolean kernel command line parameter, that when set to false will prevent the conflicting framebuffers to being removed.
Since the drivers call drm_aperture_remove_conflicting_framebuffers() very early in their probe callback, this will cause the drivers' probe to fail.
Why is that better than just modprobe.blacklisting those drivers?
Because would allow to deny list all native (as Thomas called it) DRM drivers and only allow the simpledrm driver to be probed. This is useful for distros, since could add a "Basic graphics mode" to the boot menu entries, that could boot the kernel passing a "drm.disable_native_drivers=1" cmdline option.
That way, if there's any problem with a given DRM driver, the distro may be installed and booted using the simpledrm driver and troubleshoot why a native DRM driver is not working. Or try updating the kernel package, etc.
For troubleshooting, it'll be helpful if this new parameter can be enabled for the boot via the kernel command line, then disabled again after boot-up. One simple possibility for this would be allowing the parameter to be changed via /sys/module
That's already the case with the current patch, i.e:
$ grep -o drm.* /proc/cmdline drm.disable_native_drivers=1
$ cat /proc/fb 0 simpledrm
$ modprobe virtio_gpu
$ dmesg [ 125.731549] [drm] pci: virtio-vga detected at 0000:00:01.0 [ 125.732410] virtio_gpu: probe of virtio0 failed with error -16
$ echo 0 > /sys/module/drm/parameters/disable_native_drivers
$ modprobe virtio_gpu
$ dmesg [ 187.889136] [drm] pci: virtio-vga detected at 0000:00:01.0 [ 187.894578] Console: switching to colour dummy device 80x25 [ 187.897090] virtio-pci 0000:00:01.0: vgaarb: deactivate vga console [ 187.899983] [drm] features: -virgl +edid -resource_blob -host_visible [ 187.907176] [drm] number of scanouts: 1 [ 187.907714] [drm] number of cap sets: 0 [ 187.914108] [drm] Initialized virtio_gpu 0.1.0 0 for virtio0 on minor 1 [ 187.930807] Console: switching to colour frame buffer device 128x48 [ 187.938737] virtio_gpu virtio0: [drm] fb0: virtio_gpu frame buffer device
$ cat /proc/fb 0 virtio_gpu
/drm/parameters/<name>, which I suspect doesn't work with the patch as is (due to the 0600 permissions).
I followed the convention used by other drm module parameters, hence the 0600. Do you mean that for this parameter we should be less restrictive ?
Best regards,
On Mon, Oct 25, 2021 at 8:28 AM Javier Martinez Canillas javierm@redhat.com wrote:
Hello Michel,
On 10/25/21 12:45, Michel Dänzer wrote:
On 2021-10-24 22:32, Javier Martinez Canillas wrote:
Hello Ville,
On 10/22/21 21:12, Ville Syrjälä wrote:
On Fri, Oct 22, 2021 at 04:40:40PM +0200, Javier Martinez Canillas wrote:
The simpledrm driver allows to use the frame buffer that was set-up by the firmware. This gives early video output before the platform DRM driver is probed and takes over.
But it would be useful to have a way to disable this take over by the real DRM drivers. For example, there may be bugs in the DRM drivers that could cause the display output to not work correctly.
For those cases, it would be good to keep the simpledrm driver instead and at least get a working display as set-up by the firmware.
Let's add a drm.remove_fb boolean kernel command line parameter, that when set to false will prevent the conflicting framebuffers to being removed.
Since the drivers call drm_aperture_remove_conflicting_framebuffers() very early in their probe callback, this will cause the drivers' probe to fail.
Why is that better than just modprobe.blacklisting those drivers?
Because would allow to deny list all native (as Thomas called it) DRM drivers and only allow the simpledrm driver to be probed. This is useful for distros, since could add a "Basic graphics mode" to the boot menu entries, that could boot the kernel passing a "drm.disable_native_drivers=1" cmdline option.
That way, if there's any problem with a given DRM driver, the distro may be installed and booted using the simpledrm driver and troubleshoot why a native DRM driver is not working. Or try updating the kernel package, etc.
For troubleshooting, it'll be helpful if this new parameter can be enabled for the boot via the kernel command line, then disabled again after boot-up. One simple possibility for this would be allowing the parameter to be changed via /sys/module
That's already the case with the current patch, i.e:
$ grep -o drm.* /proc/cmdline drm.disable_native_drivers=1
$ cat /proc/fb 0 simpledrm
$ modprobe virtio_gpu
$ dmesg [ 125.731549] [drm] pci: virtio-vga detected at 0000:00:01.0 [ 125.732410] virtio_gpu: probe of virtio0 failed with error -16
$ echo 0 > /sys/module/drm/parameters/disable_native_drivers
$ modprobe virtio_gpu
$ dmesg [ 187.889136] [drm] pci: virtio-vga detected at 0000:00:01.0 [ 187.894578] Console: switching to colour dummy device 80x25 [ 187.897090] virtio-pci 0000:00:01.0: vgaarb: deactivate vga console [ 187.899983] [drm] features: -virgl +edid -resource_blob -host_visible [ 187.907176] [drm] number of scanouts: 1 [ 187.907714] [drm] number of cap sets: 0 [ 187.914108] [drm] Initialized virtio_gpu 0.1.0 0 for virtio0 on minor 1 [ 187.930807] Console: switching to colour frame buffer device 128x48 [ 187.938737] virtio_gpu virtio0: [drm] fb0: virtio_gpu frame buffer device
$ cat /proc/fb 0 virtio_gpu
/drm/parameters/<name>, which I suspect doesn't work with the patch as is (due to the 0600 permissions).
I followed the convention used by other drm module parameters, hence the 0600. Do you mean that for this parameter we should be less restrictive ?
I would think that the 600 permissions would still permit it, since the root user can still access and manipulate it.
On 2021-10-25 14:28, Javier Martinez Canillas wrote:
Hello Michel,
On 10/25/21 12:45, Michel Dänzer wrote:
On 2021-10-24 22:32, Javier Martinez Canillas wrote:
Hello Ville,
On 10/22/21 21:12, Ville Syrjälä wrote:
On Fri, Oct 22, 2021 at 04:40:40PM +0200, Javier Martinez Canillas wrote:
The simpledrm driver allows to use the frame buffer that was set-up by the firmware. This gives early video output before the platform DRM driver is probed and takes over.
But it would be useful to have a way to disable this take over by the real DRM drivers. For example, there may be bugs in the DRM drivers that could cause the display output to not work correctly.
For those cases, it would be good to keep the simpledrm driver instead and at least get a working display as set-up by the firmware.
Let's add a drm.remove_fb boolean kernel command line parameter, that when set to false will prevent the conflicting framebuffers to being removed.
Since the drivers call drm_aperture_remove_conflicting_framebuffers() very early in their probe callback, this will cause the drivers' probe to fail.
Why is that better than just modprobe.blacklisting those drivers?
Because would allow to deny list all native (as Thomas called it) DRM drivers and only allow the simpledrm driver to be probed. This is useful for distros, since could add a "Basic graphics mode" to the boot menu entries, that could boot the kernel passing a "drm.disable_native_drivers=1" cmdline option.
That way, if there's any problem with a given DRM driver, the distro may be installed and booted using the simpledrm driver and troubleshoot why a native DRM driver is not working. Or try updating the kernel package, etc.
For troubleshooting, it'll be helpful if this new parameter can be enabled for the boot via the kernel command line, then disabled again after boot-up. One simple possibility for this would be allowing the parameter to be changed via /sys/module
That's already the case with the current patch, i.e:
$ grep -o drm.* /proc/cmdline drm.disable_native_drivers=1
$ cat /proc/fb 0 simpledrm
$ modprobe virtio_gpu
$ dmesg [ 125.731549] [drm] pci: virtio-vga detected at 0000:00:01.0 [ 125.732410] virtio_gpu: probe of virtio0 failed with error -16
$ echo 0 > /sys/module/drm/parameters/disable_native_drivers
$ modprobe virtio_gpu
$ dmesg [ 187.889136] [drm] pci: virtio-vga detected at 0000:00:01.0 [ 187.894578] Console: switching to colour dummy device 80x25 [ 187.897090] virtio-pci 0000:00:01.0: vgaarb: deactivate vga console [ 187.899983] [drm] features: -virgl +edid -resource_blob -host_visible [ 187.907176] [drm] number of scanouts: 1 [ 187.907714] [drm] number of cap sets: 0 [ 187.914108] [drm] Initialized virtio_gpu 0.1.0 0 for virtio0 on minor 1 [ 187.930807] Console: switching to colour frame buffer device 128x48 [ 187.938737] virtio_gpu virtio0: [drm] fb0: virtio_gpu frame buffer device
$ cat /proc/fb 0 virtio_gpu
/drm/parameters/<name>, which I suspect doesn't work with the patch as is (due to the 0600 permissions).
I followed the convention used by other drm module parameters, hence the 0600. Do you mean that for this parameter we should be less restrictive ?
No, it was simply a brain fart on my part. :}
Thanks for confirming this works!
dri-devel@lists.freedesktop.org
-
Javier Martinez Canillas -
Michel Dänzer -
Neal Gompa -
Thomas Zimmermann -
Ville Syrjälä