Re: [Intel-gfx] [PATCH 1/3] drm/atomic-helpers: remove legacy_cursor_update hacks

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On Thu, Oct 22, 2020 at 10:02 AM Rob Clark <robdclark@xxxxxxxxx> wrote:
>
> On Wed, Oct 21, 2020 at 9:32 AM Daniel Vetter <daniel.vetter@xxxxxxxx> wrote:
> >
> > The stuff never really worked, and leads to lots of fun because it
> > out-of-order frees atomic states. Which upsets KASAN, among other
> > things.
> >
> > For async updates we now have a more solid solution with the
> > ->atomic_async_check and ->atomic_async_commit hooks. Support for that
> > for msm and vc4 landed. nouveau and i915 have their own commit
> > routines, doing something similar.
> >
> > For everyone else it's probably better to remove the use-after-free
> > bug, and encourage folks to use the async support instead. The
> > affected drivers which register a legacy cursor plane and don't either
> > use the new async stuff or their own commit routine are: amdgpu,
> > atmel, mediatek, qxl, rockchip, sti, sun4i, tegra, virtio, and vmwgfx.
> >
> > Inspired by an amdgpu bug report.
> >
> > v2: Drop RFC, I think with amdgpu converted over to use
> > atomic_async_check/commit done in
> >
> > commit 674e78acae0dfb4beb56132e41cbae5b60f7d662
> > Author: Nicholas Kazlauskas <nicholas.kazlauskas@xxxxxxx>
> > Date:   Wed Dec 5 14:59:07 2018 -0500
> >
> >     drm/amd/display: Add fast path for cursor plane updates
> >
> > we don't have any driver anymore where we have userspace expecting
> > solid legacy cursor support _and_ they are using the atomic helpers in
> > their fully glory. So we can retire this.
> >
> > References: https://bugzilla.kernel.org/show_bug.cgi?id=199425
> > Cc: mikita.lipski@xxxxxxx
> > Cc: Michel Dänzer <michel@xxxxxxxxxxx>
> > Cc: harry.wentland@xxxxxxx
> > Signed-off-by: Daniel Vetter <daniel.vetter@xxxxxxxxx>
>
> This *completely* destroys fps when there is cursor movement, it would
> be a pretty bad regression, so nak

Which I *guess* is due to dpu not wiring up the plane->async_* funcs,
effectively making cursor updates synchronous.. but it will take some
time to sort out :-(

> BR,
> -R
>
> > ---
> >  drivers/gpu/drm/drm_atomic_helper.c | 13 -------------
> >  1 file changed, 13 deletions(-)
> >
> > diff --git a/drivers/gpu/drm/drm_atomic_helper.c b/drivers/gpu/drm/drm_atomic_helper.c
> > index a7bcb4b4586c..549a31e6042c 100644
> > --- a/drivers/gpu/drm/drm_atomic_helper.c
> > +++ b/drivers/gpu/drm/drm_atomic_helper.c
> > @@ -1481,13 +1481,6 @@ drm_atomic_helper_wait_for_vblanks(struct drm_device *dev,
> >         int i, ret;
> >         unsigned crtc_mask = 0;
> >
> > -        /*
> > -         * Legacy cursor ioctls are completely unsynced, and userspace
> > -         * relies on that (by doing tons of cursor updates).
> > -         */
> > -       if (old_state->legacy_cursor_update)
> > -               return;
> > -
> >         for_each_oldnew_crtc_in_state(old_state, crtc, old_crtc_state, new_crtc_state, i) {
> >                 if (!new_crtc_state->active)
> >                         continue;
> > @@ -2106,12 +2099,6 @@ int drm_atomic_helper_setup_commit(struct drm_atomic_state *state,
> >                         continue;
> >                 }
> >
> > -               /* Legacy cursor updates are fully unsynced. */
> > -               if (state->legacy_cursor_update) {
> > -                       complete_all(&commit->flip_done);
> > -                       continue;
> > -               }
> > -
> >                 if (!new_crtc_state->event) {
> >                         commit->event = kzalloc(sizeof(*commit->event),
> >                                                 GFP_KERNEL);
> > --
> > 2.28.0
> >
> > _______________________________________________
> > Intel-gfx mailing list
> > Intel-gfx@xxxxxxxxxxxxxxxxxxxxx
> > https://lists.freedesktop.org/mailman/listinfo/intel-gfx
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