diff options
Diffstat (limited to 'drivers/gpu/drm/drm_atomic_helper.c')
| -rw-r--r-- | drivers/gpu/drm/drm_atomic_helper.c | 46 |
1 files changed, 29 insertions, 17 deletions
diff --git a/drivers/gpu/drm/drm_atomic_helper.c b/drivers/gpu/drm/drm_atomic_helper.c index 29c3115bf9e2..57a84555a6bd 100644 --- a/drivers/gpu/drm/drm_atomic_helper.c +++ b/drivers/gpu/drm/drm_atomic_helper.c @@ -1832,17 +1832,21 @@ EXPORT_SYMBOL(drm_atomic_helper_commit); /** * DOC: implementing nonblocking commit * - * Nonblocking atomic commits have to be implemented in the following sequence: + * Nonblocking atomic commits should use struct &drm_crtc_commit to sequence + * different operations against each another. Locks, especially struct + * &drm_modeset_lock, should not be held in worker threads or any other + * asynchronous context used to commit the hardware state. * - * 1. Run drm_atomic_helper_prepare_planes() first. This is the only function - * which commit needs to call which can fail, so we want to run it first and + * drm_atomic_helper_commit() implements the recommended sequence for + * nonblocking commits, using drm_atomic_helper_setup_commit() internally: + * + * 1. Run drm_atomic_helper_prepare_planes(). Since this can fail and we + * need to propagate out of memory/VRAM errors to userspace, it must be called * synchronously. * * 2. Synchronize with any outstanding nonblocking commit worker threads which - * might be affected the new state update. This can be done by either cancelling - * or flushing the work items, depending upon whether the driver can deal with - * cancelled updates. Note that it is important to ensure that the framebuffer - * cleanup is still done when cancelling. + * might be affected by the new state update. This is handled by + * drm_atomic_helper_setup_commit(). * * Asynchronous workers need to have sufficient parallelism to be able to run * different atomic commits on different CRTCs in parallel. The simplest way to @@ -1853,21 +1857,29 @@ EXPORT_SYMBOL(drm_atomic_helper_commit); * must be done as one global operation, and enabling or disabling a CRTC can * take a long time. But even that is not required. * + * IMPORTANT: A &drm_atomic_state update for multiple CRTCs is sequenced + * against all CRTCs therein. Therefore for atomic state updates which only flip + * planes the driver must not get the struct &drm_crtc_state of unrelated CRTCs + * in its atomic check code: This would prevent committing of atomic updates to + * multiple CRTCs in parallel. In general, adding additional state structures + * should be avoided as much as possible, because this reduces parallelism in + * (nonblocking) commits, both due to locking and due to commit sequencing + * requirements. + * * 3. The software state is updated synchronously with * drm_atomic_helper_swap_state(). Doing this under the protection of all modeset - * locks means concurrent callers never see inconsistent state. And doing this - * while it's guaranteed that no relevant nonblocking worker runs means that - * nonblocking workers do not need grab any locks. Actually they must not grab - * locks, for otherwise the work flushing will deadlock. + * locks means concurrent callers never see inconsistent state. Note that commit + * workers do not hold any locks; their access is only coordinated through + * ordering. If workers would access state only through the pointers in the + * free-standing state objects (currently not the case for any driver) then even + * multiple pending commits could be in-flight at the same time. * * 4. Schedule a work item to do all subsequent steps, using the split-out * commit helpers: a) pre-plane commit b) plane commit c) post-plane commit and * then cleaning up the framebuffers after the old framebuffer is no longer - * being displayed. - * - * The above scheme is implemented in the atomic helper libraries in - * drm_atomic_helper_commit() using a bunch of helper functions. See - * drm_atomic_helper_setup_commit() for a starting point. + * being displayed. The scheduled work should synchronize against other workers + * using the &drm_crtc_commit infrastructure as needed. See + * drm_atomic_helper_setup_commit() for more details. */ static int stall_checks(struct drm_crtc *crtc, bool nonblock) @@ -2096,7 +2108,7 @@ EXPORT_SYMBOL(drm_atomic_helper_setup_commit); * * This function waits for all preceeding commits that touch the same CRTC as * @old_state to both be committed to the hardware (as signalled by - * drm_atomic_helper_commit_hw_done) and executed by the hardware (as signalled + * drm_atomic_helper_commit_hw_done()) and executed by the hardware (as signalled * by calling drm_crtc_send_vblank_event() on the &drm_crtc_state.event). * * This is part of the atomic helper support for nonblocking commits, see |