diff --git a/drivers/gpu/drm/drm_vblank.c b/drivers/gpu/drm/drm_vblank.c index c99feda25dea..9c6899758bc9 100644 --- a/drivers/gpu/drm/drm_vblank.c +++ b/drivers/gpu/drm/drm_vblank.c @@ -106,7 +106,7 @@ static void store_vblank(struct drm_device *dev, unsigned int pipe, write_seqlock(&vblank->seqlock); vblank->time = t_vblank; - vblank->count += vblank_count_inc; + atomic64_add(vblank_count_inc, &vblank->count); write_sequnlock(&vblank->seqlock); } @@ -272,7 +272,8 @@ static void drm_update_vblank_count(struct drm_device *dev, unsigned int pipe, DRM_DEBUG_VBL("updating vblank count on crtc %u:" " current=%llu, diff=%u, hw=%u hw_last=%u\n", - pipe, vblank->count, diff, cur_vblank, vblank->last); + pipe, atomic64_read(&vblank->count), diff, + cur_vblank, vblank->last); if (diff == 0) { WARN_ON_ONCE(cur_vblank != vblank->last); @@ -294,11 +295,23 @@ static void drm_update_vblank_count(struct drm_device *dev, unsigned int pipe, static u64 drm_vblank_count(struct drm_device *dev, unsigned int pipe) { struct drm_vblank_crtc *vblank = &dev->vblank[pipe]; + u64 count; if (WARN_ON(pipe >= dev->num_crtcs)) return 0; - return vblank->count; + count = atomic64_read(&vblank->count); + + /* + * This read barrier corresponds to the implicit write barrier of the + * write seqlock in store_vblank(). Note that this is the only place + * where we need an explicit barrier, since all other access goes + * through drm_vblank_count_and_time(), which already has the required + * read barrier curtesy of the read seqlock. + */ + smp_rmb(); + + return count; } /** @@ -763,6 +776,14 @@ drm_get_last_vbltimestamp(struct drm_device *dev, unsigned int pipe, * vblank interrupt (since it only reports the software vblank counter), see * drm_crtc_accurate_vblank_count() for such use-cases. * + * Note that for a given vblank counter value drm_crtc_handle_vblank() + * and drm_crtc_vblank_count() or drm_crtc_vblank_count_and_time() + * provide a barrier: Any writes done before calling + * drm_crtc_handle_vblank() will be visible to callers of the later + * functions, iff the vblank count is the same or a later one. + * + * See also &drm_vblank_crtc.count. + * * Returns: * The software vblank counter. */ @@ -800,7 +821,7 @@ static u64 drm_vblank_count_and_time(struct drm_device *dev, unsigned int pipe, do { seq = read_seqbegin(&vblank->seqlock); - vblank_count = vblank->count; + vblank_count = atomic64_read(&vblank->count); *vblanktime = vblank->time; } while (read_seqretry(&vblank->seqlock, seq)); @@ -817,6 +838,14 @@ static u64 drm_vblank_count_and_time(struct drm_device *dev, unsigned int pipe, * vblank events since the system was booted, including lost events due to * modesetting activity. Returns corresponding system timestamp of the time * of the vblank interval that corresponds to the current vblank counter value. + * + * Note that for a given vblank counter value drm_crtc_handle_vblank() + * and drm_crtc_vblank_count() or drm_crtc_vblank_count_and_time() + * provide a barrier: Any writes done before calling + * drm_crtc_handle_vblank() will be visible to callers of the later + * functions, iff the vblank count is the same or a later one. + * + * See also &drm_vblank_crtc.count. */ u64 drm_crtc_vblank_count_and_time(struct drm_crtc *crtc, ktime_t *vblanktime) @@ -1807,6 +1836,14 @@ EXPORT_SYMBOL(drm_handle_vblank); * * This is the native KMS version of drm_handle_vblank(). * + * Note that for a given vblank counter value drm_crtc_handle_vblank() + * and drm_crtc_vblank_count() or drm_crtc_vblank_count_and_time() + * provide a barrier: Any writes done before calling + * drm_crtc_handle_vblank() will be visible to callers of the later + * functions, iff the vblank count is the same or a later one. + * + * See also &drm_vblank_crtc.count. + * * Returns: * True if the event was successfully handled, false on failure. */ diff --git a/include/drm/drm_vblank.h b/include/drm/drm_vblank.h index 9fe4ba8bc622..c16c44052b3d 100644 --- a/include/drm/drm_vblank.h +++ b/include/drm/drm_vblank.h @@ -109,9 +109,20 @@ struct drm_vblank_crtc { seqlock_t seqlock; /** - * @count: Current software vblank counter. + * @count: + * + * Current software vblank counter. + * + * Note that for a given vblank counter value drm_crtc_handle_vblank() + * and drm_crtc_vblank_count() or drm_crtc_vblank_count_and_time() + * provide a barrier: Any writes done before calling + * drm_crtc_handle_vblank() will be visible to callers of the later + * functions, iff the vblank count is the same or a later one. + * + * IMPORTANT: This guarantee requires barriers, therefor never access + * this field directly. Use drm_crtc_vblank_count() instead. */ - u64 count; + atomic64_t count; /** * @time: Vblank timestamp corresponding to @count. */