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

[Shankar, Uma]

> -----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 ?

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