Originally by Seth Forshee seth.forshee@canonical.com, 2012-10-04: During graphics driver initialization it's useful to be able to mux only the DDC to the inactive client in order to read the EDID. Add a switch_ddc callback to allow capable handlers to provide this functionality, and add vga_switcheroo_switch_ddc() to allow DRM to mux only the DDC.
Modified by Dave Airlie airlied@gmail.com, 2012-12-22: I can't figure out why I didn't like this, but I rewrote this [...] to lock/unlock the ddc lines [...]. I think I'd prefer something like that otherwise the interface got really ugly.
Modified by Lukas Wunner lukas@wunner.de, 2015-04 - 2015-10: Change semantics of ->switch_ddc handler callback to return previous DDC owner. Original version tried to determine previous DDC owner with find_active_client() but this fails if the inactive client registers before the active client.
Don't lock vgasr_mutex in _lock_ddc() / _unlock_ddc(), it can cause deadlocks because (a) during switch (with vgasr_mutex already held), GPU is woken and probes its outputs, tries to re-acquire vgasr_mutex to lock DDC lines; (b) Likewise during switch, GPU is suspended and calls cancel_delayed_work_sync() to stop output polling, if poll task is running at this moment we may wait forever for it to finish.
Instead, lock mux_hw_lock when unregistering the handler because the only reason why we'd want to lock vgasr_mutex in _lock_ddc() / _unlock_ddc() is to block the handler from disappearing while DDC lines are switched.
Also acquire mux_hw_lock in stage2 to avoid race condition where reading the EDID and switching happens simultaneously. Likewise on MIGD / MDIS commands and on runtime suspend.
v2.1: Overhaul locking, squash commits (Daniel Vetter)
v2.2: Readability improvements (Thierry Reding)
v2.3: Overhaul locking once more
v2.4: Retain semantics of ->switchto handler callback to switch all pins, including DDC (Daniel Vetter)
v5: Rename ddc_lock to mux_hw_lock: Since we acquire this both when calling ->switch_ddc and ->switchto, it protects not just access to the DDC lines but to the mux in general. This is in line with the DRM convention to use low-level locks to avoid concurrent hw access (e.g. i2c, dp_aux) which are often called hw_lock (Daniel Vetter)
Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=88861 Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=61115 Tested-by: Lukas Wunner lukas@wunner.de [MBP 9,1 2012 intel IVB + nvidia GK107 pre-retina 15"] Cc: Seth Forshee seth.forshee@canonical.com Cc: Dave Airlie airlied@gmail.com Signed-off-by: Lukas Wunner lukas@wunner.de --- drivers/gpu/vga/vga_switcheroo.c | 97 +++++++++++++++++++++++++++++++++++++++- include/linux/vga_switcheroo.h | 8 ++++ 2 files changed, 103 insertions(+), 2 deletions(-)
diff --git a/drivers/gpu/vga/vga_switcheroo.c b/drivers/gpu/vga/vga_switcheroo.c index 81da941..56287ae 100644 --- a/drivers/gpu/vga/vga_switcheroo.c +++ b/drivers/gpu/vga/vga_switcheroo.c @@ -73,9 +73,17 @@ * there can thus be up to three clients: Two vga clients (GPUs) and one audio * client (on the discrete GPU). The code is mostly prepared to support * machines with more than two GPUs should they become available. + * * The GPU to which the outputs are currently switched is called the * active client in vga_switcheroo parlance. The GPU not in use is the - * inactive client. + * inactive client. When the inactive client's DRM driver is loaded, + * it will be unable to probe the panel's EDID and hence depends on + * VBIOS to provide its display modes. If the VBIOS modes are bogus or + * if there is no VBIOS at all (which is common on the MacBook Pro), + * a client may alternatively request that the DDC lines are temporarily + * switched to it, provided that the handler supports this. Switching + * only the DDC lines and not the entire output avoids unnecessary + * flickering. */
/** @@ -126,6 +134,9 @@ static DEFINE_MUTEX(vgasr_mutex); * @clients: list of registered clients * @handler: registered handler * @handler_flags: flags of registered handler + * @mux_hw_lock: protects mux state + * (in particular while DDC lines are temporarily switched) + * @old_ddc_owner: client to which DDC lines will be switched back on unlock * * vga_switcheroo private data. Currently only one vga_switcheroo instance * per system is supported. @@ -143,6 +154,8 @@ struct vgasr_priv {
const struct vga_switcheroo_handler *handler; enum vga_switcheroo_handler_flags_t handler_flags; + struct mutex mux_hw_lock; + int old_ddc_owner; };
#define ID_BIT_AUDIO 0x100 @@ -157,6 +170,7 @@ static void vga_switcheroo_debugfs_fini(struct vgasr_priv *priv); /* only one switcheroo per system */ static struct vgasr_priv vgasr_priv = { .clients = LIST_HEAD_INIT(vgasr_priv.clients), + .mux_hw_lock = __MUTEX_INITIALIZER(vgasr_priv.mux_hw_lock), };
static bool vga_switcheroo_ready(void) @@ -226,6 +240,7 @@ EXPORT_SYMBOL(vga_switcheroo_register_handler); void vga_switcheroo_unregister_handler(void) { mutex_lock(&vgasr_mutex); + mutex_lock(&vgasr_priv.mux_hw_lock); vgasr_priv.handler_flags = 0; vgasr_priv.handler = NULL; if (vgasr_priv.active) { @@ -233,6 +248,7 @@ void vga_switcheroo_unregister_handler(void) vga_switcheroo_debugfs_fini(&vgasr_priv); vgasr_priv.active = false; } + mutex_unlock(&vgasr_priv.mux_hw_lock); mutex_unlock(&vgasr_mutex); } EXPORT_SYMBOL(vga_switcheroo_unregister_handler); @@ -432,6 +448,76 @@ void vga_switcheroo_client_fb_set(struct pci_dev *pdev, EXPORT_SYMBOL(vga_switcheroo_client_fb_set);
/** + * vga_switcheroo_lock_ddc() - temporarily switch DDC lines to a given client + * @pdev: client pci device + * + * Temporarily switch DDC lines to the client identified by @pdev + * (but leave the outputs otherwise switched to where they are). + * This allows the inactive client to probe EDID. The DDC lines must + * afterwards be switched back by calling vga_switcheroo_unlock_ddc(), + * even if this function returns an error. + * + * Return: Previous DDC owner on success or a negative int on error. + * Specifically, %-ENODEV if no handler has registered or if the handler + * does not support switching the DDC lines. Also, a negative value + * returned by the handler is propagated back to the caller. + * The return value has merely an informational purpose for any caller + * which might be interested in it. It is acceptable to ignore the return + * value and simply rely on the result of the subsequent EDID probe, + * which will be %NULL if DDC switching failed. + */ +int vga_switcheroo_lock_ddc(struct pci_dev *pdev) +{ + enum vga_switcheroo_client_id id; + + mutex_lock(&vgasr_priv.mux_hw_lock); + if (!vgasr_priv.handler || !vgasr_priv.handler->switch_ddc) { + vgasr_priv.old_ddc_owner = -ENODEV; + return -ENODEV; + } + + id = vgasr_priv.handler->get_client_id(pdev); + vgasr_priv.old_ddc_owner = vgasr_priv.handler->switch_ddc(id); + return vgasr_priv.old_ddc_owner; +} +EXPORT_SYMBOL(vga_switcheroo_lock_ddc); + +/** + * vga_switcheroo_unlock_ddc() - switch DDC lines back to previous owner + * @pdev: client pci device + * + * Switch DDC lines back to the previous owner after calling + * vga_switcheroo_lock_ddc(). This must be called even if + * vga_switcheroo_lock_ddc() returned an error. + * + * Return: Previous DDC owner on success (i.e. the client identifier of @pdev) + * or a negative int on error. + * Specifically, %-ENODEV if no handler has registered or if the handler + * does not support switching the DDC lines. Also, a negative value + * returned by the handler is propagated back to the caller. + * Finally, invoking this function without calling vga_switcheroo_lock_ddc() + * first is not allowed and will result in %-EINVAL. + */ +int vga_switcheroo_unlock_ddc(struct pci_dev *pdev) +{ + enum vga_switcheroo_client_id id; + int ret = vgasr_priv.old_ddc_owner; + + if (WARN_ON_ONCE(!mutex_is_locked(&vgasr_priv.mux_hw_lock))) + return -EINVAL; + + if (vgasr_priv.old_ddc_owner >= 0) { + id = vgasr_priv.handler->get_client_id(pdev); + if (vgasr_priv.old_ddc_owner != id) + ret = vgasr_priv.handler->switch_ddc( + vgasr_priv.old_ddc_owner); + } + mutex_unlock(&vgasr_priv.mux_hw_lock); + return ret; +} +EXPORT_SYMBOL(vga_switcheroo_unlock_ddc); + +/** * DOC: Manual switching and manual power control * * In this mode of use, the file /sys/kernel/debug/vgaswitcheroo/switch @@ -568,7 +654,9 @@ static int vga_switchto_stage2(struct vga_switcheroo_client *new_client) console_unlock(); }
+ mutex_lock(&vgasr_priv.mux_hw_lock); ret = vgasr_priv.handler->switchto(new_client->id); + mutex_unlock(&vgasr_priv.mux_hw_lock); if (ret) return ret;
@@ -683,7 +771,9 @@ vga_switcheroo_debugfs_write(struct file *filp, const char __user *ubuf, vgasr_priv.delayed_switch_active = false;
if (just_mux) { + mutex_lock(&vgasr_priv.mux_hw_lock); ret = vgasr_priv.handler->switchto(client_id); + mutex_unlock(&vgasr_priv.mux_hw_lock); goto out; }
@@ -895,8 +985,11 @@ static int vga_switcheroo_runtime_suspend(struct device *dev) if (ret) return ret; mutex_lock(&vgasr_mutex); - if (vgasr_priv.handler->switchto) + if (vgasr_priv.handler->switchto) { + mutex_lock(&vgasr_priv.mux_hw_lock); vgasr_priv.handler->switchto(VGA_SWITCHEROO_IGD); + mutex_unlock(&vgasr_priv.mux_hw_lock); + } vga_switcheroo_power_switch(pdev, VGA_SWITCHEROO_OFF); mutex_unlock(&vgasr_mutex); return 0; diff --git a/include/linux/vga_switcheroo.h b/include/linux/vga_switcheroo.h index a745f4f0..b39a5f3 100644 --- a/include/linux/vga_switcheroo.h +++ b/include/linux/vga_switcheroo.h @@ -102,6 +102,9 @@ enum vga_switcheroo_client_id { * Mandatory. For muxless machines this should be a no-op. Returning 0 * denotes success, anything else failure (in which case the switch is * aborted) + * @switch_ddc: switch DDC lines to given client. + * Optional. Should return the previous DDC owner on success or a + * negative int on failure * @power_state: cut or reinstate power of given client. * Optional. The return value is ignored * @get_client_id: determine if given pci device is integrated or discrete GPU. @@ -113,6 +116,7 @@ enum vga_switcheroo_client_id { struct vga_switcheroo_handler { int (*init)(void); int (*switchto)(enum vga_switcheroo_client_id id); + int (*switch_ddc)(enum vga_switcheroo_client_id id); int (*power_state)(enum vga_switcheroo_client_id id, enum vga_switcheroo_state state); enum vga_switcheroo_client_id (*get_client_id)(struct pci_dev *pdev); @@ -156,6 +160,8 @@ int vga_switcheroo_register_handler(const struct vga_switcheroo_handler *handler enum vga_switcheroo_handler_flags_t handler_flags); void vga_switcheroo_unregister_handler(void); enum vga_switcheroo_handler_flags_t vga_switcheroo_handler_flags(void); +int vga_switcheroo_lock_ddc(struct pci_dev *pdev); +int vga_switcheroo_unlock_ddc(struct pci_dev *pdev);
int vga_switcheroo_process_delayed_switch(void);
@@ -179,6 +185,8 @@ static inline int vga_switcheroo_register_audio_client(struct pci_dev *pdev, enum vga_switcheroo_client_id id) { return 0; } static inline void vga_switcheroo_unregister_handler(void) {} static inline enum vga_switcheroo_handler_flags_t vga_switcheroo_handler_flags(void) { return 0; } +static inline int vga_switcheroo_lock_ddc(struct pci_dev *pdev) { return -ENODEV; } +static inline int vga_switcheroo_unlock_ddc(struct pci_dev *pdev) { return -ENODEV; } static inline int vga_switcheroo_process_delayed_switch(void) { return 0; } static inline enum vga_switcheroo_state vga_switcheroo_get_client_state(struct pci_dev *dev) { return VGA_SWITCHEROO_ON; }