On 06/10, Maxime Ripard wrote:
> When doing an asynchronous page flip (PAGE_FLIP ioctl with the
> DRM_MODE_PAGE_FLIP_ASYNC flag set), the current code waits for the
> possible GPU buffer being rendered through a call to
> vc4_queue_seqno_cb().
>
> On the BCM2835-37, the GPU driver is part of the vc4 driver and that
> function is defined in vc4_gem.c to wait for the buffer to be rendered,
> and once it's done, call a callback.
>
> However, on the BCM2711 used on the RaspberryPi4, the GPU driver is
> separate (v3d) and that function won't do anything. This was working
> because we were going into a path, due to uninitialized variables, that
> was always scheduling the callback.
>
> However, we were never actually waiting for the buffer to be rendered
> which was resulting in frames being displayed out of order.
>
> The generic API to signal those kind of completion in the kernel are the
> DMA fences, and fortunately the v3d drivers supports them and signal
> when its job is done. That API also provides an equivalent function that
> allows to have a callback being executed when the fence is signalled as
> done.
>
> Let's change our driver a bit to rely on the previous function for the
> older SoCs, and on DMA fences for the BCM2711.
>
> Signed-off-by: Maxime Ripard <max...@cerno.tech>
> ---
> drivers/gpu/drm/vc4/vc4_crtc.c | 50 +++++++++++++++++++++++++++++++---
> 1 file changed, 46 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/gpu/drm/vc4/vc4_crtc.c b/drivers/gpu/drm/vc4/vc4_crtc.c
> index a3c04d6cbd20..9355213dc883 100644
> --- a/drivers/gpu/drm/vc4/vc4_crtc.c
> +++ b/drivers/gpu/drm/vc4/vc4_crtc.c
> @@ -776,6 +776,7 @@ struct vc4_async_flip_state {
> struct drm_pending_vblank_event *event;
>
> union {
> + struct dma_fence_cb fence;
> struct vc4_seqno_cb seqno;
> } cb;
> };
> @@ -835,6 +836,50 @@ static void vc4_async_page_flip_seqno_complete(struct
> vc4_seqno_cb *cb)
> vc4_bo_dec_usecnt(bo);
> }
>
> +static void vc4_async_page_flip_fence_complete(struct dma_fence *fence,
> + struct dma_fence_cb *cb)
> +{
> + struct vc4_async_flip_state *flip_state =
> + container_of(cb, struct vc4_async_flip_state, cb.fence);
> +
> + vc4_async_page_flip_complete(flip_state);
> + dma_fence_put(fence);
> +}
> +
> +static int vc4_async_set_fence_cb(struct drm_device *dev,
> + struct vc4_async_flip_state *flip_state)
> +{
> + struct drm_framebuffer *fb = flip_state->fb;
> + struct drm_gem_cma_object *cma_bo = drm_fb_cma_get_gem_obj(fb, 0);
> + struct vc4_dev *vc4 = to_vc4_dev(dev);
> + struct dma_fence *fence;
> + int ret;
> +
> + if (!vc4->is_vc5) {
> + struct vc4_bo *bo = to_vc4_bo(&cma_bo->base);
> +
> + return vc4_queue_seqno_cb(dev, &flip_state->cb.seqno, bo->seqno,
> + vc4_async_page_flip_seqno_complete);
> + }
> +
> + ret = dma_resv_get_singleton(cma_bo->base.resv, DMA_RESV_USAGE_READ,
> &fence);
> + if (ret)
> + return ret;
> +
> + /* If there's no fence, complete the page flip immediately */
> + if (!fence) {
> + vc4_async_page_flip_fence_complete(fence,
> &flip_state->cb.fence);
> + return 0;
> + }
Hi,this change lgtm. Reviewed-by: Melissa Wen <m...@igalia.com> Thanks > + > + /* If the fence has already been completed, complete the page flip */ > + if (dma_fence_add_callback(fence, &flip_state->cb.fence, > + vc4_async_page_flip_fence_complete)) > + vc4_async_page_flip_fence_complete(fence, > &flip_state->cb.fence); > + > + return 0; > +} > + > static int > vc4_async_page_flip_common(struct drm_crtc *crtc, > struct drm_framebuffer *fb, > @@ -844,8 +889,6 @@ vc4_async_page_flip_common(struct drm_crtc *crtc, > struct drm_device *dev = crtc->dev; > struct drm_plane *plane = crtc->primary; > struct vc4_async_flip_state *flip_state; > - struct drm_gem_cma_object *cma_bo = drm_fb_cma_get_gem_obj(fb, 0); > - struct vc4_bo *bo = to_vc4_bo(&cma_bo->base); > > flip_state = kzalloc(sizeof(*flip_state), GFP_KERNEL); > if (!flip_state) > @@ -876,8 +919,7 @@ vc4_async_page_flip_common(struct drm_crtc *crtc, > */ > drm_atomic_set_fb_for_plane(plane->state, fb); > > - vc4_queue_seqno_cb(dev, &flip_state->cb.seqno, bo->seqno, > - vc4_async_page_flip_seqno_complete); > + vc4_async_set_fence_cb(dev, flip_state); > > /* Driver takes ownership of state on successful async commit. */ > return 0; > -- > 2.36.1 >
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