[Intel-gfx] [PATCH 4/5] drm/i915/frontbuffer: Remove early frontbuffer flush in prepare_plane_fb()

[Ville Syrjälä]

On Wed, Feb 28, 2018 at 10:28:13PM +0200, Ville Syrjälä wrote:
> On Sat, Feb 24, 2018 at 03:24:55AM +0000, Pandiyan, Dhinakaran wrote:
> > 
> > 
> > 
> > On Mon, 2018-02-19 at 10:07 +0100, Maarten Lankhorst wrote:
> > > Op 16-02-18 om 20:27 schreef Pandiyan, Dhinakaran:
> > > > On Fri, 2018-02-16 at 08:55 +0000, Chris Wilson wrote:
> > > >> Quoting Dhinakaran Pandiyan (2018-02-16 04:33:21)
> > > >>> Preparing a framebuffer should not require a flush. _post_plane_update()
> > > >>> takes care of flushing when a flip is scheduled, this should be
> > > >>> sufficient for PSR and FBC.
> > > >> Makes sense.
> > > >>  
> > > > I also think this might speed up the flips a bit by avoiding flushes. 
> > > >
> > > >>> Cc: Paulo Zanoni <paulo.r.zanoni at intel.com>
> > > >>> Cc: Ville Syrjälä <ville.syrjala at linux.intel.com>
> > > >>> Cc: Chris Wilson <chris at chris-wilson.co.uk>
> > > >>> Signed-off-by: Dhinakaran Pandiyan <dhinakaran.pandiyan at intel.com>
> > > >> Also
> > > >> Cc: Maarten Lankhorst <maarten.lankhorst at linux.intel.com>
> > > >> to validate the flow through atomic.
> > > >> -Chris
> > > >>
> > > Page flips used to do intel_frontbuffer_flip_prepare here, followed by intel_frontbuffer_flip_complete. I think it would make sense to change the patch to do that?
> > > 
> > 
> > I have no context why it was removed, I'll have to understand that
> > change and get back to you.
> 
> Since we supposedly have hw nuke for both fbc and psr there doesn't seem
> to be much need to do anything for flips. I guess DRRS is the only
> thing that kinda needs it (not really, just avoids flipping with the
> slow timings). But I think DRRS should really be tied into the vblank
> stuff somehow so that we switch to the fast timings whenever a vblank
> interrupts are enabled.

Oh, I guess VLV/CHV PSR is what would need this. To do that properly
(ie. main link off) I think we'd basically need to do a full modeset
when exiting PSR, so it should probably handled somewhere higher up
during modeset, and for other uses the frontbuffer tracking
should perhaps just schedule a work to do the full modeset.

-- 
Ville Syrjälä
Intel OTC