[Intel-gfx] [PATCH v2 3/9] drm/i915: Enable default_phase in GCP when possible

[Konduru, Chandra]

> > > @@ -560,6 +560,49 @@ static bool hdmi_sink_is_deep_color(struct
> > > drm_encoder *encoder)
> > >  	return false;
> > >  }
> > >
> > > +/*
> > > + * Determine if default_phase=1 can be indicated in the GCP infoframe.
> > > + *
> > > + * From HDMI specification 1.4a:
> > > + * - The first pixel of each Video Data Period shall always have a
> > > +pixel packing phase of 0
> > > + * - The first pixel following each Video Data Period shall have a
> > > +pixel packing phase of 0
> > > + * - The PP bits shall be constant for all GCPs and will be equal to
> > > +the last packing phase
> > > + * - The first pixel following every transition of HSYNC or VSYNC shall have a
> > > pixel packing
> > > + *   phase of 0
> > > + */
> > > +static bool gcp_default_phase_possible(int pipe_bpp,
> > > +				       const struct drm_display_mode *mode) {
> > > +	unsigned int pixels_per_group;
> > > +
> > > +	switch (pipe_bpp) {
> > > +	case 30:
> > > +		/* 4 pixels in 5 clocks */
> > > +		pixels_per_group = 4;
> > > +		break;
> > > +	case 36:
> > > +		/* 2 pixels in 3 clocks */
> > > +		pixels_per_group = 2;
> > > +		break;
> > > +	case 48:
> > > +		/* 1 pixel in 2 clocks */
> > > +		pixels_per_group = 1;
> > > +		break;
> > > +	default:
> > > +		/* phase information not relevant for 8bpc */
> > > +		return false;
> > > +	}
> > > +
> > > +	return mode->crtc_hdisplay % pixels_per_group == 0 &&
> > > +		mode->crtc_htotal % pixels_per_group == 0 &&
> > > +		mode->crtc_hblank_start % pixels_per_group == 0 &&
> > > +		mode->crtc_hblank_end % pixels_per_group == 0 &&
> > > +		mode->crtc_hsync_start % pixels_per_group == 0 &&
> > > +		mode->crtc_hsync_end % pixels_per_group == 0 &&
> >
> > For hsync, bspec says Hsync is an even number.
> > Isn't it above check should be something like (hsync_end - hsync_start) % 2 ==
> 0?
> > And similarly for front & back porches, right?
> 
> If X and Y are even then (X - Y) is even too. Also the text in bspec is
> less informative than the text in HDMI spec, which is why I quited the
> HDMI spec instead.

Sure, if X and Y are even X - Y is even, but it is more restrictive check than
needed. Because if both X and Y are odd, X - Y is even, and in that case
above code doesn't allow to use default phase. Which may be OK, but
it didn't truly allow default phase when possible.