[Intel-gfx] [PATCH 7/8] drm/i915/display/skl+: Drop frontbuffer rendering support

[Ville Syrjälä]

On Wed, Aug 25, 2021 at 03:47:12PM +0300, Ville Syrjälä wrote:
> On Wed, Aug 25, 2021 at 12:49:25AM +0000, Souza, Jose wrote:
> > On Thu, 2021-08-19 at 19:07 +0300, Ville Syrjälä wrote:
> > > On Wed, Aug 18, 2021 at 07:48:03PM +0000, Souza, Jose wrote:
> > > > On Wed, 2021-08-18 at 17:55 +0300, Ville Syrjälä wrote:
> > > > > On Tue, Aug 17, 2021 at 05:42:15PM -0700, José Roberto de Souza wrote:
> > > > > > By now all the userspace applications should have migrated to atomic
> > > > > > or at least be calling DRM_IOCTL_MODE_DIRTYFB.
> > > > > > 
> > > > > > With that we can kill frontbuffer rendering support in i915 for
> > > > > > modern platforms.
> > > > > > 
> > > > > > So here converting legacy APIs into atomic commits so it can be
> > > > > > properly handled by driver i915.
> > > > > > 
> > > > > > Several IGT tests will fail with this changes, because some tests
> > > > > > were stressing those frontbuffer rendering scenarios that no userspace
> > > > > > should be using by now, fixes to IGT should be sent soon.
> > > > > 
> > > > > Blocking atomic commits instead of the current lightweight frontbuffer
> > > > > interface sounds like a terrible plan. How unusable is X with this
> > > > > approach?
> > > > 
> > > > 100% usable, had no issues when running X in TGL and ADL-P.
> > > > Added a debug message in intel_user_framebuffer_dirty() and X is not even using frontbuffer rendering at all.
> > > 
> > > Turn off your compositor if you want to test front buffer rendering.
> > 
> > Worked fine on Plasma with a 4K panel, was not able to find how to do that in Gnome.
> 
> I didn't think you can turn off composition with either one of those.
> You actually confirmed it's running with everytithing unredirected and
> eg. there was no lag moving windows around and wiggling the mouse?
> 
> Avoiding that lag is pretty much the sole reason why the legacy
> cursor unsynced update stuff even exists in the driver. Hard to
> imagine you wouldn't hit the same issue with the server getting
> blocked on dirtyfb all the time.

Oh and running x11perf/etc. to see the impact on the raw numbers would
probably be good idea.

-- 
Ville Syrjälä
Intel