Originally by Seth Forshee <seth.forshee at 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 at 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 at wunner.de>, 2015-08-14: 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 ddc_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 lock ddc_lock in stage2 to avoid race condition where reading the EDID and switching happens simultaneously. Likewise on MIGD / MDIS commands and on runtime suspend. Retain semantics of ->switchto handler callback to switch all pins, including DDC. 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. v2.1: Overhaul locking, squash commits (requested by Daniel Vetter <daniel.vetter at ffwll.ch>) v2.2: Readability improvements (requested by Thierry Reding <thierry.reding at gmail.com>) v2.3: Overhaul locking once more v2.4: Retain semantics of ->switchto handler callback to switch all pins (requested by Daniel Vetter <daniel.vetter at ffwll.ch>) Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=88861 Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=61115 Tested-by: Pierre Moreau <pierre.morrow at free.fr> [MBP 5,3 2009 nvidia MCP79 + G96 pre-retina 15"] Tested-by: William Brown <william at blackhats.net.au> [MBP 8,2 2011 intel SNB + amd turks pre-retina 15"] Tested-by: Lukas Wunner <lukas at wunner.de> [MBP 9,1 2012 intel IVB + nvidia GK107 pre-retina 15"] Cc: Seth Forshee <seth.forshee at canonical.com> Cc: Dave Airlie <airlied at gmail.com> Signed-off-by: Lukas Wunner <lukas at wunner.de> --- drivers/gpu/vga/vga_switcheroo.c | 98 +++++++++++++++++++++++++++++++++++++++- include/linux/vga_switcheroo.h | 9 ++++ 2 files changed, 105 insertions(+), 2 deletions(-) diff --git a/drivers/gpu/vga/vga_switcheroo.c b/drivers/gpu/vga/vga_switcheroo.c index aa077aa..9b6946e 100644 --- a/drivers/gpu/vga/vga_switcheroo.c +++ b/drivers/gpu/vga/vga_switcheroo.c @@ -73,9 +73,19 @@ * 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. On machines which are able to mux external connectors, + * VBIOS cannot know of attached displays so switching the DDC lines + * is the only option to retrieve the displays' EDID. */ /** @@ -125,6 +135,8 @@ static DEFINE_MUTEX(vgasr_mutex); * (counting only vga clients, not audio clients) * @clients: list of registered clients * @handler: registered handler + * @ddc_lock: protects access to DDC lines while they 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. @@ -141,6 +153,8 @@ struct vgasr_priv { struct list_head clients; struct vga_switcheroo_handler *handler; + struct mutex ddc_lock; + int old_ddc_owner; }; #define ID_BIT_AUDIO 0x100 @@ -155,6 +169,7 @@ 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), + .ddc_lock = __MUTEX_INITIALIZER(vgasr_priv.ddc_lock), }; static bool vga_switcheroo_ready(void) @@ -221,12 +236,14 @@ EXPORT_SYMBOL(vga_switcheroo_register_handler); void vga_switcheroo_unregister_handler(void) { mutex_lock(&vgasr_mutex); + mutex_lock(&vgasr_priv.ddc_lock); vgasr_priv.handler = NULL; if (vgasr_priv.active) { pr_info("disabled\n"); vga_switcheroo_debugfs_fini(&vgasr_priv); vgasr_priv.active = false; } + mutex_unlock(&vgasr_priv.ddc_lock); mutex_unlock(&vgasr_mutex); } EXPORT_SYMBOL(vga_switcheroo_unregister_handler); @@ -412,6 +429,76 @@ 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.ddc_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.ddc_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.ddc_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 @@ -548,7 +635,9 @@ static int vga_switchto_stage2(struct vga_switcheroo_client *new_client) console_unlock(); } + mutex_lock(&vgasr_priv.ddc_lock); ret = vgasr_priv.handler->switchto(new_client->id); + mutex_unlock(&vgasr_priv.ddc_lock); if (ret) return ret; @@ -663,7 +752,9 @@ vga_switcheroo_debugfs_write(struct file *filp, const char __user *ubuf, vgasr_priv.delayed_switch_active = false; if (just_mux) { + mutex_lock(&vgasr_priv.ddc_lock); ret = vgasr_priv.handler->switchto(client_id); + mutex_unlock(&vgasr_priv.ddc_lock); goto out; } @@ -875,8 +966,11 @@ 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.ddc_lock); vgasr_priv.handler->switchto(VGA_SWITCHEROO_IGD); + mutex_unlock(&vgasr_priv.ddc_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 b2a3dda..6edaacc 100644 --- a/include/linux/vga_switcheroo.h +++ b/include/linux/vga_switcheroo.h @@ -82,6 +82,9 @@ 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. @@ -93,6 +96,7 @@ 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); @@ -132,6 +136,9 @@ int vga_switcheroo_register_audio_client(struct pci_dev *pdev, void vga_switcheroo_client_fb_set(struct pci_dev *dev, struct fb_info *info); +int vga_switcheroo_lock_ddc(struct pci_dev *pdev); +int vga_switcheroo_unlock_ddc(struct pci_dev *pdev); + int vga_switcheroo_register_handler(struct vga_switcheroo_handler *handler); void vga_switcheroo_unregister_handler(void); @@ -150,6 +157,8 @@ static inline void vga_switcheroo_unregister_client(struct pci_dev *dev) {} static inline int vga_switcheroo_register_client(struct pci_dev *dev, const struct vga_switcheroo_client_ops *ops, bool driver_power_control) { return 0; } static inline void vga_switcheroo_client_fb_set(struct pci_dev *dev, struct fb_info *info) {} +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_register_handler(struct vga_switcheroo_handler *handler) { return 0; } static inline int vga_switcheroo_register_audio_client(struct pci_dev *pdev, const struct vga_switcheroo_client_ops *ops, -- 1.8.5.2 (Apple Git-48)