From 9953f41799bdad34c367196541a7a9a3b6e13a6c Mon Sep 17 00:00:00 2001 From: Daniel Vetter Date: Fri, 4 Dec 2015 09:46:02 +0100 Subject: [PATCH] drm: Kerneldoc for drm_mode_config_funcs The meat here is definitely the detailed specs for what atomic_check and atomic_commit are supposed to do. And another candidate for a core vfunc that should be in a helper really (output_poll_changed this time around). v2: Feedback from Eric on irc: - spelling fixes. - spec what async should do - copy the event related paragraphs from page_flip and adjust - make it clear that a successful async commit is not allowed to leave the pipe dead or disabled. v3: Use FIXME comments to annotate functions that we should move to some helpers. v4: Suggestions from Thierry. Cc: Eric Anholt Signed-off-by: Daniel Vetter Link: http://patchwork.freedesktop.org/patch/msgid/1449218769-16577-22-git-send-email-daniel.vetter@ffwll.ch Reviewed-by: Thierry Reding --- include/drm/drm_crtc.h | 243 +++++++++++++++++++++++++++++++++++++++-- 1 file changed, 233 insertions(+), 10 deletions(-) diff --git a/include/drm/drm_crtc.h b/include/drm/drm_crtc.h index f09391f9cac0..4f587a5bc88f 100644 --- a/include/drm/drm_crtc.h +++ b/include/drm/drm_crtc.h @@ -1715,31 +1715,254 @@ struct drm_mode_set { /** * struct drm_mode_config_funcs - basic driver provided mode setting functions - * @fb_create: create a new framebuffer object - * @output_poll_changed: function to handle output configuration changes - * @atomic_check: check whether a given atomic state update is possible - * @atomic_commit: commit an atomic state update previously verified with - * atomic_check() - * @atomic_state_alloc: allocate a new atomic state - * @atomic_state_clear: clear the atomic state - * @atomic_state_free: free the atomic state * * Some global (i.e. not per-CRTC, connector, etc) mode setting functions that * involve drivers. */ struct drm_mode_config_funcs { + /** + * @fb_create: + * + * Create a new framebuffer object. The core does basic checks on the + * requested metadata, but most of that is left to the driver. See + * struct &drm_mode_fb_cmd2 for details. + * + * RETURNS: + * + * A new framebuffer with an initial reference count of 1 or a negative + * error code encoded with ERR_PTR(). + */ struct drm_framebuffer *(*fb_create)(struct drm_device *dev, struct drm_file *file_priv, const struct drm_mode_fb_cmd2 *mode_cmd); + + /** + * @output_poll_changed: + * + * Callback used by helpers to inform the driver of output configuration + * changes. + * + * Drivers implementing fbdev emulation with the helpers can call + * drm_fb_helper_hotplug_changed from this hook to inform the fbdev + * helper of output changes. + * + * FIXME: + * + * Except that there's no vtable for device-level helper callbacks + * there's no reason this is a core function. + */ void (*output_poll_changed)(struct drm_device *dev); + /** + * @atomic_check: + * + * This is the only hook to validate an atomic modeset update. This + * function must reject any modeset and state changes which the hardware + * or driver doesn't support. This includes but is of course not limited + * to: + * + * - Checking that the modes, framebuffers, scaling and placement + * requirements and so on are within the limits of the hardware. + * + * - Checking that any hidden shared resources are not oversubscribed. + * This can be shared PLLs, shared lanes, overall memory bandwidth, + * display fifo space (where shared between planes or maybe even + * CRTCs). + * + * - Checking that virtualized resources exported to userspace are not + * oversubscribed. For various reasons it can make sense to expose + * more planes, crtcs or encoders than which are physically there. One + * example is dual-pipe operations (which generally should be hidden + * from userspace if when lockstepped in hardware, exposed otherwise), + * where a plane might need 1 hardware plane (if it's just on one + * pipe), 2 hardware planes (when it spans both pipes) or maybe even + * shared a hardware plane with a 2nd plane (if there's a compatible + * plane requested on the area handled by the other pipe). + * + * - Check that any transitional state is possible and that if + * requested, the update can indeed be done in the vblank period + * without temporarily disabling some functions. + * + * - Check any other constraints the driver or hardware might have. + * + * - This callback also needs to correctly fill out the &drm_crtc_state + * in this update to make sure that drm_atomic_crtc_needs_modeset() + * reflects the nature of the possible update and returns true if and + * only if the update cannot be applied without tearing within one + * vblank on that CRTC. The core uses that information to reject + * updates which require a full modeset (i.e. blanking the screen, or + * at least pausing updates for a substantial amount of time) if + * userspace has disallowed that in its request. + * + * - The driver also does not need to repeat basic input validation + * like done for the corresponding legacy entry points. The core does + * that before calling this hook. + * + * See the documentation of @atomic_commit for an exhaustive list of + * error conditions which don't have to be checked at the + * ->atomic_check() stage? + * + * See the documentation for struct &drm_atomic_state for how exactly + * an atomic modeset update is described. + * + * Drivers using the atomic helpers can implement this hook using + * drm_atomic_helper_check(), or one of the exported sub-functions of + * it. + * + * RETURNS: + * + * 0 on success or one of the below negative error codes: + * + * - -EINVAL, if any of the above constraints are violated. + * + * - -EDEADLK, when returned from an attempt to acquire an additional + * &drm_modeset_lock through drm_modeset_lock(). + * + * - -ENOMEM, if allocating additional state sub-structures failed due + * to lack of memory. + * + * - -EINTR, -EAGAIN or -ERESTARTSYS, if the IOCTL should be restarted. + * This can either be due to a pending signal, or because the driver + * needs to completely bail out to recover from an exceptional + * situation like a GPU hang. From a userspace point all errors are + * treated equally. + */ int (*atomic_check)(struct drm_device *dev, - struct drm_atomic_state *a); + struct drm_atomic_state *state); + + /** + * @atomic_commit: + * + * This is the only hook to commit an atomic modeset update. The core + * guarantees that @atomic_check has been called successfully before + * calling this function, and that nothing has been changed in the + * interim. + * + * See the documentation for struct &drm_atomic_state for how exactly + * an atomic modeset update is described. + * + * Drivers using the atomic helpers can implement this hook using + * drm_atomic_helper_commit(), or one of the exported sub-functions of + * it. + * + * Asynchronous commits (as indicated with the async parameter) must + * do any preparatory work which might result in an unsuccessful commit + * in the context of this callback. The only exceptions are hardware + * errors resulting in -EIO. But even in that case the driver must + * ensure that the display pipe is at least running, to avoid + * compositors crashing when pageflips don't work. Anything else, + * specifically committing the update to the hardware, should be done + * without blocking the caller. For updates which do not require a + * modeset this must be guaranteed. + * + * The driver must wait for any pending rendering to the new + * framebuffers to complete before executing the flip. It should also + * wait for any pending rendering from other drivers if the underlying + * buffer is a shared dma-buf. Asynchronous commits must not wait for + * rendering in the context of this callback. + * + * An application can request to be notified when the atomic commit has + * completed. These events are per-CRTC and can be distinguished by the + * CRTC index supplied in &drm_event to userspace. + * + * The drm core will supply a struct &drm_event in the event + * member of each CRTC's &drm_crtc_state structure. This can be handled by the + * drm_crtc_send_vblank_event() function, which the driver should call on + * the provided event upon completion of the atomic commit. Note that if + * the driver supports vblank signalling and timestamping the vblank + * counters and timestamps must agree with the ones returned from page + * flip events. With the current vblank helper infrastructure this can + * be achieved by holding a vblank reference while the page flip is + * pending, acquired through drm_crtc_vblank_get() and released with + * drm_crtc_vblank_put(). Drivers are free to implement their own vblank + * counter and timestamp tracking though, e.g. if they have accurate + * timestamp registers in hardware. + * + * NOTE: + * + * Drivers are not allowed to shut down any display pipe successfully + * enabled through an atomic commit on their own. Doing so can result in + * compositors crashing if a page flip is suddenly rejected because the + * pipe is off. + * + * RETURNS: + * + * 0 on success or one of the below negative error codes: + * + * - -EBUSY, if an asynchronous updated is requested and there is + * an earlier updated pending. Drivers are allowed to support a queue + * of outstanding updates, but currently no driver supports that. + * Note that drivers must wait for preceding updates to complete if a + * synchronous update is requested, they are not allowed to fail the + * commit in that case. + * + * - -ENOMEM, if the driver failed to allocate memory. Specifically + * this can happen when trying to pin framebuffers, which must only + * be done when committing the state. + * + * - -ENOSPC, as a refinement of the more generic -ENOMEM to indicate + * that the driver has run out of vram, iommu space or similar GPU + * address space needed for framebuffer. + * + * - -EIO, if the hardware completely died. + * + * - -EINTR, -EAGAIN or -ERESTARTSYS, if the IOCTL should be restarted. + * This can either be due to a pending signal, or because the driver + * needs to completely bail out to recover from an exceptional + * situation like a GPU hang. From a userspace point of view all errors are + * treated equally. + * + * This list is exhaustive. Specifically this hook is not allowed to + * return -EINVAL (any invalid requests should be caught in + * @atomic_check) or -EDEADLK (this function must not acquire + * additional modeset locks). + */ int (*atomic_commit)(struct drm_device *dev, - struct drm_atomic_state *a, + struct drm_atomic_state *state, bool async); + + /** + * @atomic_state_alloc: + * + * This optional hook can be used by drivers that want to subclass struct + * &drm_atomic_state to be able to track their own driver-private global + * state easily. If this hook is implemented, drivers must also + * implement @atomic_state_clear and @atomic_state_free. + * + * RETURNS: + * + * A new &drm_atomic_state on success or NULL on failure. + */ struct drm_atomic_state *(*atomic_state_alloc)(struct drm_device *dev); + + /** + * @atomic_state_clear: + * + * This hook must clear any driver private state duplicated into the + * passed-in &drm_atomic_state. This hook is called when the caller + * encountered a &drm_modeset_lock deadlock and needs to drop all + * already acquired locks as part of the deadlock avoidance dance + * implemented in drm_modeset_lock_backoff(). + * + * Any duplicated state must be invalidated since a concurrent atomic + * update might change it, and the drm atomic interfaces always apply + * updates as relative changes to the current state. + * + * Drivers that implement this must call drm_atomic_state_default_clear() + * to clear common state. + */ void (*atomic_state_clear)(struct drm_atomic_state *state); + + /** + * @atomic_state_free: + * + * This hook needs driver private resources and the &drm_atomic_state + * itself. Note that the core first calls drm_atomic_state_clear() to + * avoid code duplicate between the clear and free hooks. + * + * Drivers that implement this must call drm_atomic_state_default_free() + * to release common resources. + */ void (*atomic_state_free)(struct drm_atomic_state *state); }; -- 2.30.2