Re: [Intel-gfx] [Intel-xe] [PATCH] drm/xe/display: Do not use i915 frontbuffer tracking implementation

["Ville Syrjälä" <ville.syrjala@linux.intel.com>]

On Wed, Mar 08, 2023 at 03:29:45PM +0100, Maarten Lankhorst wrote:
> Hey,
> 
> 
> On 2023-03-08 14:36, Ville Syrjälä wrote:
> > On Wed, Mar 08, 2023 at 01:47:12PM +0100, Maarten Lankhorst wrote:
> >> On 2023-03-06 21:58, Ville Syrjälä wrote:
> >>> On Mon, Mar 06, 2023 at 09:23:50PM +0100, Maarten Lankhorst wrote:
> >>>> Hey,
> >>>>
> >>>> On 2023-03-06 16:23, Souza, Jose wrote:
> >>>>> On Mon, 2023-03-06 at 15:16 +0100, Maarten Lankhorst wrote:
> >>>>>> As a fallback if we decide not to merge the frontbuffer tracking, allow
> >>>>>> i915 to keep its own implementation, and do the right thing in Xe.
> >>>>>>
> >>>>>> The frontbuffer tracking for Xe is still done per-fb, while i915 can
> >>>>>> keep doing the weird intel_frontbuffer + i915_active thing without
> >>>>>> blocking Xe.
> >>>>> Please also disable PSR and FBC with this or at least add a way for users to disable those features.
> >>>>> Without frontbuffer tracker those two features will break in some cases.
> >>>> FBC and PSR work completely as expected. I don't remove frontbuffer
> >>>> tracking; I only remove the GEM parts.
> >>>>
> >>>> Explicit invalidation using pageflip or CPU rendering + DirtyFB continue
> >>>> to work, as I validated on my laptop with FBC.
> >>> Neither of which are relevant to the removal of the gem hooks.
> >>>
> >>> Like I already said ~10 times in the last meeting, we need a proper
> >>> testcase. Here's a rough idea what it should do:
> >>>
> >>> prepare a batch with
> >>> 1. spinner
> >>> 2. something that clobbers the fb
> >>>
> >>> Then
> >>> 1. grab reference crc
> >>> 2. execbuffer
> >>> 3. dirtyfb
> >>> 4. wait long enough for fbc to recompress
> >>> 5. terminate spinner
> >>> 6. gem_sync
> >>> 7. grab crc and compare with reference
> >>>
> >>> No idea what the current status of PSR+CRC is, so not sure
> >>> whether we can actually test PSR or not.
> >> This test doesn't make sense. DirtyFB should simply not return before
> >> execbuffer finishes.
> > Of course it should. It's not a blocking ioctl, and can't
> > be because that will make X unusable.
> 
> Except it actually is.
> 
> DirtyFB blocks in its default implementation, and waits for the next vblank.
> 
> drm_atomic_helper_dirtyfb() blocks by default as it's a synchronous 
> plane update.
> 
> Considering every driver except i915 uses it, it works just fine. :)

No it doesn't. We tries to use it, but that was an utter failure.

-- 
Ville Syrjälä
Intel