[Intel-gfx] [PATCH v2 3/5] drm/i915/display: Workaround cursor left overs with PSR2 selective fetch enabled

[Ville Syrjälä]

On Thu, Sep 16, 2021 at 05:09:08PM +0000, Souza, Jose wrote:
> On Thu, 2021-09-16 at 16:17 +0300, Ville Syrjälä wrote:
> > On Wed, Sep 15, 2021 at 06:18:35PM +0000, Souza, Jose wrote:
> > > On Wed, 2021-09-15 at 17:58 +0300, Ville Syrjälä wrote:
> > > > On Tue, Sep 14, 2021 at 02:25:05PM -0700, José Roberto de Souza wrote:
> > > > > Not sure why but when moving the cursor fast it causes some artifacts
> > > > > of the cursor to be left in the cursor path, adding some pixels above
> > > > > the cursor to the damaged area fixes the issue, so leaving this as a
> > > > > workaround until proper fix is found.
> > > > 
> > > > Have you tried warping the cursor clear across the screen while
> > > > a partial update is already pending? I think it will go badly.
> > > 
> > > You mean move the cursor for example from 0x0 to 500x500 in one frame?
> > > It will mark as damaged the previous area and the new one.
> > 
> > Legacy cursor updates bypass all that stuff so you're not going to
> > updating the sel fetch area for the other planes.
> > 
> > > 
> > > > 
> > > > In fact I'm thinking the mailbox style legacy cursor updates are just
> > > > fundementally incompatible with partial updates since the cursor
> > > > can move outside of the already committed update region any time.
> > > > Ie. I suspect while the cursor is visible we simply can't do partial
> > > > updates.
> > > 
> > > Probably I did not understand what you want to say, but each cursor update will be in one frame, updating the necessary area.
> > 
> > The legacy cursor uses mailbox updates so there is no 1:1 relationship
> > between actual scanned out frames and cursor ioctl calls. You can
> > have umpteen thousand cursor updates per frame.
> 
> Not if intel_legacy_cursor_update() is changed to go to the slow path and do one atomic commit for each move.
> https://patchwork.freedesktop.org/patch/453192/?series=94522&rev=1

That's not going to fly. The whole reason for the legacy cursor thing is
that X likes to do thousands of cursor updates per frame.

> 
> I believe compositors will do a single atomic commit updating cursor and all the other planes into a single commit.

No. X obviously doesn't do that. And IIRC chromeos also uses the
legacy cursor ioctl for the cursor despite using atomic commits for
everything else.

-- 
Ville Syrjälä
Intel