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

[Souza, Jose]

On Wed, 2021-09-22 at 16:41 +0300, Ville Syrjälä wrote:
> On Tue, Sep 21, 2021 at 10:37:53PM +0000, Souza, Jose wrote:
> > On Tue, 2021-09-21 at 16:35 +0300, Ville Syrjälä wrote:
> > > On Fri, Sep 17, 2021 at 09:33:59PM +0000, Souza, Jose wrote:
> > > > On Fri, 2021-09-17 at 20:49 +0300, Ville Syrjälä wrote:
> > > > > On Fri, Sep 17, 2021 at 05:02:21PM +0000, Souza, Jose wrote:
> > > > > > On Fri, 2021-09-17 at 16:04 +0300, Ville Syrjälä wrote:
> > > > > > > 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.
> > > > > > 
> > > > > > From user experience perspective there is no issues in converting to atomic commit, those 3 videos that I shared with you have this conversion. 
> > > > > 
> > > > > I don't know what you've tested but the legacy cursor fastpath is very
> > > > > much needed. We've have numerous bug reports whenever it has
> > > > > accidentally regressed, and I've witnessed the carnage myself as well.
> > > > > Hmm, I guess you didn't actually disable it fully. To do that you
> > > > > would have to clear state->legacy_cursor_update explicitly somewhere.
> > > > 
> > > > Thanks for pointing out state->legacy_cursor_update and yes setting it to false makes causes the cursor to lag.
> > > > 
> > > > > 
> > > > > Either way I just retested the earlier patches just with the nonblocking
> > > > > commit for dirtyfb hacked in, and I left the cursor code using the
> > > > > half fast path you made it take. The user experience is still as bad
> > > > > as before. Just moving the mouse around makes glxgears stutter, and the
> > > > > reported fps drops to ~400 from that alone. And doing anything more
> > > > > involved like moving windows around is still a total fail.
> > > > 
> > > > I have tested it in a TGL and ADL-P, will try to get some gen9 to try it.
> > > > Other than that I don't know what could this big difference between our setups.
> > > > I'm using Mate like you with 'enable software compositing window manager' disabled.
> > > 
> > > Not sure.
> > > 
> > > BTW another thing I noticed is that the sel_fetch coordinate calculation
> > > code seems super confused:
> > > - it seems to do operations between coordinates that don't even live in
> > >   the same coordinate space (eg. drm_rect_intersect(&clip, &src) where
> > >   clip is the straight userspace damage coordinates but src is
> > >   PLANE_SURF relative plane source coordinates)
> > 
> > On the first for_each_oldnew_intel_plane_in_state() it calculates the plane damaged area and then in the last 3 lines converts it to pipe coordinate
> > space.
> > The second for_each_oldnew_intel_plane_in_state() takes the pipe coordinate space damaged area and sets new_plane_state->psr2_sel_fetch_area with the
> > plane coordinate space damaged area.
> 
> There are many many coordinate spaces we use:
> - relative to user fb origin: userspace provided dirtyfb and plane src
>   coordinates (drm_plane_state_src())
> - relative to start of gem obj: used temporarily during some calculations
> - relative to start of vma: used temporarily during some calculations
>   (also actually what intel_plane_fence_y_offset() gives you)
> - relative to PLANE_SURF: plane_state->uapi.src
> - relative to user crtc origin: drm_plane_state_dest()
> - relative to pipe origin: plane_state->uapi.dst
> 
> The sel_fetch code is now doing operations between coordinates from
> different coordinate spaces AFAICS.

It only uses this 3:
- plane damaged: that is in the same coordinate space as plane_state->uapi.src
- plane_state->uapi.src
- plane_state->uapi.dst

There is only conversions between src to dst and dst to src.

> 
> My gut feeling is that we want to do these calculations alongside the
> rest of the plane coordinate calcs in the plane code. That way we can
> just work forwards from userspace coords all the way to PLANE_SURF
> relative coords for both cases. Trying to do these sel fetch
> calculations after the fact means we're going to have to work both
> forwards and backwards at the same time, which doesn't sounds all that
> nice to me. But I've not spent a huge amount of time thinking about
> this so not 100% sure.
> 
> What we need is basically something like kms_big_fb but with sel fetch
> in mind. That could test all the interesting cases where we either use
> remapping or just hit the standard panning cases where PLANE_SURF does 
> not match the fb origin.
> 
> > 
> > > - no checks for plane scaling that I can see but it still assumes it can 
> > >   just assume a 1:1 relationship between src and dst coordinates
> > 
> > My understanding is that intel_atomic_plane_check_clipping() will adjust src to match dst width and height.
> 
> To do partial scaled updates correctly we'd need to have sub-pixel
> coordinates for the src or else you'll get a visible seam when the
> update region doesn't exactly terminate on a pixel boundary. And
> actually even if it did land on a pixel boundary you'd still get
> the seam unless we could instruct the hardware to filter across
> the edge. Don't think we can even do that with the currect hardware.

Actually scaling is not supported by the feature, so we are missing a check in intel_psr2_sel_fetch_config_valid() to disable it in this cases.

BSpec: 55229
Not supported with plane or pipe scaling. Software calculations to account for extra lines of scaler filter input and adjusted scale factor and filter
phase are too complicated.

> 
> > 
> > > - bigjoiner also affects the coordinate spaces, so that part too is probably
> > >   busted
> > > 
> > 
> > I don't think there is a commercial available eDP panel that would require bigjoiner.
> > We could definitely rule PSR2 out if such case shows up by adding a check in intel_psr2_sel_fetch_config_valid().
> > 
> 
> Yeah, if bigjoiner turns out to complicate the calculations to much we
> could just reject the combo. Not entirely sure it's a significant
> complication though.
>