[Intel-gfx] [PATCH] drm/i915/display: Add a vblank wait for FBC activation within same frame

[Ville Syrjälä]

On Thu, Sep 10, 2020 at 01:42:23PM +0000, Shankar, Uma wrote:
> 
> 
> > -----Original Message-----
> > From: Jani Nikula <jani.nikula at linux.intel.com>
> > Sent: Thursday, September 10, 2020 7:04 PM
> > To: Shankar, Uma <uma.shankar at intel.com>; intel-gfx at lists.freedesktop.org
> > Subject: Re: [Intel-gfx] [PATCH] drm/i915/display: Add a vblank wait for FBC
> > activation within same frame
> > 
> > On Thu, 10 Sep 2020, Uma Shankar <uma.shankar at intel.com> wrote:
> > > Add a vblank wait when fbc activation request comes for the same frame
> > > on TGL. This helps fix underrun related to fbc.
> > >
> > > Signed-off-by: Uma Shankar <uma.shankar at intel.com>
> > > ---
> > >  drivers/gpu/drm/i915/display/intel_fbc.c | 13 +++++++++++--
> > >  1 file changed, 11 insertions(+), 2 deletions(-)
> > >
> > > diff --git a/drivers/gpu/drm/i915/display/intel_fbc.c
> > > b/drivers/gpu/drm/i915/display/intel_fbc.c
> > > index 135f5e8a4d70..3e1d715e4a4e 100644
> > > --- a/drivers/gpu/drm/i915/display/intel_fbc.c
> > > +++ b/drivers/gpu/drm/i915/display/intel_fbc.c
> > > @@ -1055,6 +1055,7 @@ static void __intel_fbc_post_update(struct
> > > intel_crtc *crtc)  {
> > >  	struct drm_i915_private *dev_priv = to_i915(crtc->base.dev);
> > >  	struct intel_fbc *fbc = &dev_priv->fbc;
> > > +	static u32 old_frame_cnt, new_frame_cnt;
> > 
> > In the strongest terms, do not add static data. These would be shared across
> > devices, which is certainly a bug.
> 
> Oh ok, yeah will remove this. I guess adding them to intel_fbc should be ok right ?

I didn't think we found what's really going on here. So this still
seems like random duct tape which just changs some timings.

> 
> Thanks & Regards,
> Uma Shankar
> 
> > BR,
> > Jani.
> > 
> > >
> > >  	drm_WARN_ON(&dev_priv->drm, !mutex_is_locked(&fbc->lock));
> > >
> > > @@ -1075,10 +1076,18 @@ static void __intel_fbc_post_update(struct
> > intel_crtc *crtc)
> > >  	if (!intel_fbc_can_activate(crtc))
> > >  		return;
> > >
> > > -	if (!fbc->busy_bits)
> > > +	old_frame_cnt = new_frame_cnt;
> > > +	new_frame_cnt = intel_crtc_get_vblank_counter(crtc);
> > > +	if (!fbc->busy_bits) {
> > > +		if (IS_TIGERLAKE(dev_priv) &&
> > > +		    old_frame_cnt == new_frame_cnt) {
> > > +			drm_dbg_kms(&dev_priv->drm, "Wait for vblank before
> > Activating FBC");
> > > +			intel_wait_for_vblank_if_active(dev_priv, crtc->pipe);
> > > +		}
> > >  		intel_fbc_hw_activate(dev_priv);
> > > -	else
> > > +	} else {
> > >  		intel_fbc_deactivate(dev_priv, "frontbuffer write");
> > > +	}
> > >  }
> > >
> > >  void intel_fbc_post_update(struct intel_atomic_state *state,
> > 
> > --
> > Jani Nikula, Intel Open Source Graphics Center
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-- 
Ville Syrjälä
Intel