Re: [Intel-gfx] [RFC v2 01/22] drm: RFC for Plane Color Hardware Pipeline

[Pekka Paalanen <ppaalanen@gmail.com>]

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On Thu, 25 Nov 2021 20:43:19 +0000
"Shankar, Uma" <uma.shankar@intel.com> wrote:

> > -----Original Message-----
> > From: Harry Wentland <harry.wentland@amd.com>
> > Sent: Tuesday, November 23, 2021 8:35 PM
> > To: Shankar, Uma <uma.shankar@intel.com>; intel-gfx@lists.freedesktop.org; dri-
> > devel@lists.freedesktop.org
> > Cc: ville.syrjala@linux.intel.com; ppaalanen@gmail.com; brian.starkey@arm.com;
> > sebastian@sebastianwick.net; Shashank.Sharma@amd.com
> > Subject: Re: [RFC v2 01/22] drm: RFC for Plane Color Hardware Pipeline
> > 
> > 
> > 
> > On 2021-09-06 17:38, Uma Shankar wrote:  
> > > This is a RFC proposal for plane color hardware blocks.
> > > It exposes the property interface to userspace and calls out the
> > > details or interfaces created and the intended purpose.
> > >
> > > Credits: Ville Syrjälä <ville.syrjala@linux.intel.com>
> > > Signed-off-by: Uma Shankar <uma.shankar@intel.com>
> > > ---
> > >  Documentation/gpu/rfc/drm_color_pipeline.rst | 167
> > > +++++++++++++++++++
> > >  1 file changed, 167 insertions(+)
> > >  create mode 100644 Documentation/gpu/rfc/drm_color_pipeline.rst
> > >
> > > diff --git a/Documentation/gpu/rfc/drm_color_pipeline.rst
> > > b/Documentation/gpu/rfc/drm_color_pipeline.rst
> > > new file mode 100644
> > > index 000000000000..0d1ca858783b
> > > --- /dev/null
> > > +++ b/Documentation/gpu/rfc/drm_color_pipeline.rst
> > > @@ -0,0 +1,167 @@
> > > +==================================================
> > > +Display Color Pipeline: Proposed DRM Properties
> > > +==================================================
> > > +
> > > +This is how a typical display color hardware pipeline looks like:
> > > + +-------------------------------------------+
> > > + |                RAM                        |
> > > + |  +------+    +---------+    +---------+   |
> > > + |  | FB 1 |    |  FB 2   |    | FB N    |   |
> > > + |  +------+    +---------+    +---------+   |
> > > + +-------------------------------------------+
> > > +       |  Plane Color Hardware Block |
> > > + +--------------------------------------------+
> > > + | +---v-----+   +---v-------+   +---v------+ |
> > > + | | Plane A |   | Plane B   |   | Plane N  | |
> > > + | | DeGamma |   | Degamma   |   | Degamma  | |
> > > + | +---+-----+   +---+-------+   +---+------+ |
> > > + |     |             |               |        |
> > > + | +---v-----+   +---v-------+   +---v------+ |
> > > + | |Plane A  |   | Plane B   |   | Plane N  | |
> > > + | |CSC/CTM  |   | CSC/CTM   |   | CSC/CTM  | |
> > > + | +---+-----+   +----+------+   +----+-----+ |
> > > + |     |              |               |       |
> > > + | +---v-----+   +----v------+   +----v-----+ |
> > > + | | Plane A |   | Plane B   |   | Plane N  | |
> > > + | | Gamma   |   | Gamma     |   | Gamma    | |
> > > + | +---+-----+   +----+------+   +----+-----+ |
> > > + |     |              |               |       |
> > > + +--------------------------------------------+
> > > ++------v--------------v---------------v-------|
> > > +||                                           ||
> > > +||           Pipe Blender                    ||
> > > ++--------------------+------------------------+
> > > +|                    |                        |
> > > +|        +-----------v----------+             |
> > > +|        |  Pipe DeGamma        |             |
> > > +|        |                      |             |
> > > +|        +-----------+----------+             |
> > > +|                    |            Pipe Color  |
> > > +|        +-----------v----------+ Hardware    |
> > > +|        |  Pipe CSC/CTM        |             |
> > > +|        |                      |             |
> > > +|        +-----------+----------+             |
> > > +|                    |                        |
> > > +|        +-----------v----------+             |
> > > +|        |  Pipe Gamma          |             |
> > > +|        |                      |             |
> > > +|        +-----------+----------+             |
> > > +|                    |                        |
> > > ++---------------------------------------------+
> > > +                     |
> > > +                     v
> > > +               Pipe Output
> > > +  
> > 
> > This diagram defines what happens before and after the blending space but did
> > where does scaling fit into it? Scaling can look different when performed in linear or
> > non-linear space so I think it is important to define where in the pipeline it sits.
> > 
> > In my view scaling would happen between plane degamma and plane CSC.  
> 
> Yeah we can add scaling as well to make it clear. Scaling ideally should happen after
> Degamma. In intel's case it is after the CSC.

Btw. are you aware that if a plane has an alpha channel which is used
for pixel coverage (i.e. shape anti-aliasing), then non-nearest
sampling and therefore also scaling must operate on alpha
pre-multiplied optical (linear) values?

For the best results, of course.

So after degamma indeed, but you cannot degamma with pre-multiplied
alpha, yet scaling should use pre-multiplied alpha.


Thanks,
pq

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