Re: [PATCH v2 1/8] drm/i915: Add a comment exlaining CCS hsub/vsub

["Ville Syrjälä" <ville.syrjala@linux.intel.com>]

On Sat, Jan 20, 2018 at 09:39:13AM -0800, Jason Ekstrand wrote:
> Reviewed-by: Jason Ekstrand <jason@jlekstrand.net>

Thanks for the comment and review ;) Patches 1-6 have now been pushed to
dinq.

> 
> On Fri, Jan 19, 2018 at 6:41 AM, Ville Syrjala <
> ville.syrjala@linux.intel.com> wrote:
> 
> > From: Ville Syrjälä <ville.syrjala@linux.intel.com>
> >
> > Let's document why we claim hsub==8,vsub==16 for CCS.
> >
> > v2: Replace my explanation with Jason's
> >
> > Cc: Daniel Vetter <daniel@ffwll.ch>
> > Cc: Ben Widawsky <ben@bwidawsk.net>
> > Cc: Jason Ekstrand <jason@jlekstrand.net>
> > Cc: Daniel Stone <daniels@collabora.com>
> > Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
> > ---
> >  drivers/gpu/drm/i915/intel_display.c | 14 ++++++++++++++
> >  1 file changed, 14 insertions(+)
> >
> > diff --git a/drivers/gpu/drm/i915/intel_display.c
> > b/drivers/gpu/drm/i915/intel_display.c
> > index 91f3c0a64596..8d0d5d8753c0 100644
> > --- a/drivers/gpu/drm/i915/intel_display.c
> > +++ b/drivers/gpu/drm/i915/intel_display.c
> > @@ -2387,6 +2387,20 @@ static unsigned int intel_fb_modifier_to_tiling(uint64_t
> > fb_modifier)
> >         }
> >  }
> >
> > +/*
> > + * From the Sky Lake PRM:
> > + * "The Color Control Surface (CCS) contains the compression status of
> > + *  the cache-line pairs. The compression state of the cache-line pair
> > + *  is specified by 2 bits in the CCS. Each CCS cache-line represents
> > + *  an area on the main surface of 16 x16 sets of 128 byte Y-tiled
> > + *  cache-line-pairs. CCS is always Y tiled."
> > + *
> > + * Since cache line pairs refers to horizontally adjacent cache lines,
> > + * each cache line in the CCS corresponds to an area of 32x16 cache
> > + * lines on the main surface. Since each pixel is 4 bytes, this gives
> > + * us a ratio of one byte in the CCS for each 8x16 pixels in the
> > + * main surface.
> > + */
> >  static const struct drm_format_info ccs_formats[] = {
> >         { .format = DRM_FORMAT_XRGB8888, .depth = 24, .num_planes = 2,
> > .cpp = { 4, 1, }, .hsub = 8, .vsub = 16, },
> >         { .format = DRM_FORMAT_XBGR8888, .depth = 24, .num_planes = 2,
> > .cpp = { 4, 1, }, .hsub = 8, .vsub = 16, },
> > --
> > 2.13.6
> >
> >

-- 
Ville Syrjälä
Intel OTC
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