diff options
| -rw-r--r-- | drivers/gpu/drm/drm_atomic.c | 8 | ||||
| -rw-r--r-- | include/drm/drm_modeset_helper_vtables.h | 5 | ||||
| -rw-r--r-- | include/drm/drm_plane.h | 11 |
3 files changed, 21 insertions, 3 deletions
diff --git a/drivers/gpu/drm/drm_atomic.c b/drivers/gpu/drm/drm_atomic.c index 3d9ae057a6cd..9bdd67781917 100644 --- a/drivers/gpu/drm/drm_atomic.c +++ b/drivers/gpu/drm/drm_atomic.c @@ -1496,6 +1496,14 @@ EXPORT_SYMBOL(drm_atomic_set_fb_for_plane); * Otherwise, if &drm_plane_state.fence is not set this function we just set it * with the received implicit fence. In both cases this function consumes a * reference for @fence. + * + * This way explicit fencing can be used to overrule implicit fencing, which is + * important to make explicit fencing use-cases work: One example is using one + * buffer for 2 screens with different refresh rates. Implicit fencing will + * clamp rendering to the refresh rate of the slower screen, whereas explicit + * fence allows 2 independent render and display loops on a single buffer. If a + * driver allows obeys both implicit and explicit fences for plane updates, then + * it will break all the benefits of explicit fencing. */ void drm_atomic_set_fence_for_plane(struct drm_plane_state *plane_state, diff --git a/include/drm/drm_modeset_helper_vtables.h b/include/drm/drm_modeset_helper_vtables.h index 3e76ca805b0f..35e2a3a79fc5 100644 --- a/include/drm/drm_modeset_helper_vtables.h +++ b/include/drm/drm_modeset_helper_vtables.h @@ -1004,11 +1004,14 @@ struct drm_plane_helper_funcs { * This function must not block for outstanding rendering, since it is * called in the context of the atomic IOCTL even for async commits to * be able to return any errors to userspace. Instead the recommended - * way is to fill out the fence member of the passed-in + * way is to fill out the &drm_plane_state.fence of the passed-in * &drm_plane_state. If the driver doesn't support native fences then * equivalent functionality should be implemented through private * members in the plane structure. * + * Drivers which always have their buffers pinned should use + * drm_gem_fb_prepare_fb() for this hook. + * * The helpers will call @cleanup_fb with matching arguments for every * successful call to this hook. * diff --git a/include/drm/drm_plane.h b/include/drm/drm_plane.h index 9563bd25f19b..26fa50c2a50e 100644 --- a/include/drm/drm_plane.h +++ b/include/drm/drm_plane.h @@ -80,8 +80,15 @@ struct drm_plane_state { /** * @fence: * - * Optional fence to wait for before scanning out @fb. Do not write this - * directly, use drm_atomic_set_fence_for_plane() + * Optional fence to wait for before scanning out @fb. The core atomic + * code will set this when userspace is using explicit fencing. Do not + * write this directly for a driver's implicit fence, use + * drm_atomic_set_fence_for_plane() to ensure that an explicit fence is + * preserved. + * + * Drivers should store any implicit fence in this from their + * &drm_plane_helper.prepare_fb callback. See drm_gem_fb_prepare_fb() + * and drm_gem_fb_simple_display_pipe_prepare_fb() for suitable helpers. */ struct dma_fence *fence; |