[Intel-gfx] [PATCH 14/15] drm/i915: skl nv12 workarounds

[Konduru, Chandra]

> > +
> > +	if (((IS_SKYLAKE(dev) && intel_get_stepping(dev) == 'C') ||
> > +		(IS_BROXTON(dev) && intel_get_stepping(dev) == 'A')) &&
> > +		fb->pixel_format == DRM_FORMAT_NV12) {
> > +			I915_WRITE(CHICKEN_PIPESL(pipe),
> > +				I915_READ(CHICKEN_PIPESL(pipe)) |
> DISABLE_STREAMER_FIX);
> > +	}
> 
> According to Bspec this would need to be disabled for render
> compression. And to do that we'd need to add some vblank waits to make
> sure we don't disable it too soon. But since it's pre-production
> hardware anyway I guess we might not care too much.

Render compression related checks will be coming as part of that patch.

> 
> I would probably drop SKL from these since I'd assume almost everyone
> has D+ by now. And maybe just stuff it in init_clock_gating for BXT
> since we're going to eliminate it soonish anyway.

Last checked some folks are still using, so keep it intact for completeness.

> > +static void skl_wa_clkgate(struct drm_i915_private *dev_priv,
> > +	int pipe, int enable)
> > +{
> > +	if (pipe == PIPE_A || pipe == PIPE_B) {
> > +		if (enable)
> > +			I915_WRITE(CLKGATE_DIS_PSL(pipe),
> > +				DUPS1_GATING_DIS | DUPS2_GATING_DIS);
> > +		else
> > +			I915_WRITE(CLKGATE_DIS_PSL(pipe),
> > +				I915_READ(CLKGATE_DIS_PSL(pipe) &
> > +				~(DUPS1_GATING_DIS|DUPS2_GATING_DIS)));
> > +	}
> > +}
> > +
> >  static void haswell_crtc_enable(struct drm_crtc *crtc)
> >  {
> >  	struct drm_device *dev = crtc->dev;
> > @@ -5094,6 +5119,9 @@ static void haswell_crtc_enable(struct drm_crtc
> *crtc)
> >  		intel_wait_for_vblank(dev, hsw_workaround_pipe);
> >  		intel_wait_for_vblank(dev, hsw_workaround_pipe);
> >  	}
> > +
> > +	/* workaround for NV12 */
> > +	skl_wa_clkgate(dev_priv, pipe, 1);
> 
> I wonder what's the cost of having this
> a) always enabled
> b) enabled when the pipe is enabled
> c) enabled only when NV12 is used
> ?

Initially optimized to enable only when nv12 is used,
but there are some corner cases when planes switch to and 
from nv12 to non-nv12 and SV recommendation is to enable
always; and SV evaluated cost, and it isn't a big concern.