[PATCH] drm/atomic-helpers: remove legacy_cursor_update hacks

[Jason-JH Lin (林睿祥)]

On Sun, 2024-01-28 at 10:24 +0100, Maxime Ripard wrote:
> On Thu, Jan 25, 2024 at 07:17:21PM +0100, Daniel Vetter wrote:
> > On Tue, Jan 23, 2024 at 06:09:05AM +0000, Jason-JH Lin (林睿祥) wrote:
> > > Hi Maxime, Daniel,
> > > 
> > > We encountered similar issue with mediatek SoCs.
> > > 
> > > We have found that in drm_atomic_helper_commit_rpm(), when
> > > disabling
> > > the cursor plane, the old_state->legacy_cursor_update in
> > > drm_atomic_wait_for_vblank() is set to true.
> > > As the result, we are not actually waiting for a vlbank to wait
> > > for our
> > > hardware to close the cursor plane. Subsequently, the execution
> > > proceeds to drm_atomic_helper_cleanup_planes() to  free the
> > > cursor
> > > buffer. This can lead to use-after-free issues with our hardware.
> > > 
> > > Could you please apply this patch to fix our problem?
> > > Or are there any considerations for not applying this patch?
> > 
> > Mostly it needs someone to collect a pile of acks/tested-by and
> > then land
> > it.
> > 
> > I'd be _very_ happy if someone else can take care of that ...
> > 
> > There's also the potential issue that it might slow down some of
> > the
> > legacy X11 use-cases that really needed a non-blocking cursor, but
> > I think
> > all the drivers where this matters have switched over to the async
> > plane
> > update stuff meanwhile. So hopefully that's good.
> 
> I think there was also a regression with msm no one really figured
> out?

OK...
But I am only available on MediaTek platform.

Does it also causes a regression with msn if I re-send a patch for
drm_atomic_helper.c only?

Regards,
Jason-JH.Lin
> 
> Maxime