On 05/09, Melissa Wen wrote:
> O 05/09, Melissa Wen wrote:
> > On 05/03, 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 <maxime@xxxxxxxxxx>
> > > ---
> > > drivers/gpu/drm/vc4/vc4_crtc.c | 41 ++++++++++++++++++++++++++++++++--
> > > 1 file changed, 39 insertions(+), 2 deletions(-)
> > >
> > > diff --git a/drivers/gpu/drm/vc4/vc4_crtc.c b/drivers/gpu/drm/vc4/vc4_crtc.c
> > > index e0ae7bef08fa..8e1369fca937 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 +836,43 @@ 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, false, &fence);
> + for kernel bot complaint, I replaced false with `DMA_RESV_USAGE_READ`
> to run some tests
>
> > > + if (ret)
> > > + return ret;
> > > +
> > > + if (dma_fence_add_callback(fence, &flip_state->cb.fence,
me again :)
I was thinking if we should add a check here for !fence and just complete the page flip,
instead of letting `dma_fence_add_callback` warns whenever fence is NULL.
I think there are situation in which fence is NULL and it is not an
issue, right? Does it make sense?
> > > + 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,
> > > @@ -874,8 +912,7 @@ 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);
> >
> > I tried to run igt kms_async_flip, but the test still seems very tied to
> > the i915 driver. So, as far as I could check, I didn't see any red
> > flags and sync page flip behaviour seems preserved.
> >
> > >
> > > /* Driver takes ownership of state on successful async commit. */
> > > return 0;
> > > --
> > > 2.35.1
> > >
>
>
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