On Wed, May 19, 2021 at 11:38:53AM -0700, Rob Clark wrote:
> From: Rob Clark <robdcl...@chromium.org>
>
> Signed-off-by: Rob Clark <robdcl...@chromium.org>
> ---
> drivers/gpu/drm/drm_atomic_helper.c | 11 +++++++++++
> 1 file changed, 11 insertions(+)
>
> diff --git a/drivers/gpu/drm/drm_atomic_helper.c
> b/drivers/gpu/drm/drm_atomic_helper.c
> index 560aaecba31b..fe10fc2e7f86 100644
> --- a/drivers/gpu/drm/drm_atomic_helper.c
> +++ b/drivers/gpu/drm/drm_atomic_helper.c
> @@ -1435,11 +1435,15 @@ int drm_atomic_helper_wait_for_fences(struct
> drm_device *dev,
> int i, ret;
>
> for_each_new_plane_in_state(state, plane, new_plane_state, i) {
> + u64 vblank_count;
> +
> if (!new_plane_state->fence)
> continue;
>
> WARN_ON(!new_plane_state->fb);
>
> + vblank_count = drm_crtc_vblank_count(new_plane_state->crtc);
> +
> /*
> * If waiting for fences pre-swap (ie: nonblock), userspace can
> * still interrupt the operation. Instead of blocking until the
> @@ -1449,6 +1453,13 @@ int drm_atomic_helper_wait_for_fences(struct
> drm_device *dev,
> if (ret)
> return ret;
>
> + /*
> + * Check if we've missed a vblank while waiting, and if we have
> + * signal the fence that it's signaler should be boosted
> + */
> + if (vblank_count !=
> drm_crtc_vblank_count(new_plane_state->crtc))
> + dma_fence_boost(new_plane_state->fence);
I think we should do a lot better here:
- maybe only bother doing this for single-crtc updates, and only if
modeset isn't set. No one else cares about latency.
- We should boost _right_ when we've missed the frame, so I think we
should have a _timeout wait here that guesstimates when the vblank is
over (might need to throw in a vblank wait if we missed) and then boost
immediately. Not wait a bunch of frames (worst case) until we finally
decide to boost.
Otherwise I really like this, I think it's about the only real reason i915
isn't using atomic helpers.
Also adding Matt B for this topic.
-Daniel
> +
> dma_fence_put(new_plane_state->fence);
> new_plane_state->fence = NULL;
> }
> --
> 2.30.2
>
--
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
