[PATCH v3 02/17] drm/connector: Add enum documentation to drm_colorspace

[Pekka Paalanen]

On Thu, 9 Mar 2023 01:56:11 +0100
Sebastian Wick <sebastian.wick at redhat.com> wrote:

> On Wed, Mar 8, 2023 at 9:59 AM Pekka Paalanen <ppaalanen at gmail.com> wrote:
> >
> > On Tue, 7 Mar 2023 10:10:52 -0500
> > Harry Wentland <harry.wentland at amd.com> wrote:
> >  
> > > From: Joshua Ashton <joshua at froggi.es>
> > >
> > > To match the other enums, and add more information about these values.
> > >
> > > v2:
> > >  - Specify where an enum entry comes from
> > >  - Clarify DEFAULT and NO_DATA behavior
> > >  - BT.2020 CYCC is "constant luminance"
> > >  - correct type for BT.601
> > >
> > > Signed-off-by: Joshua Ashton <joshua at froggi.es>
> > > Signed-off-by: Harry Wentland <harry.wentland at amd.com>
> > > Reviewed-by: Harry Wentland <harry.wentland at amd.com>  
> >
> > Hi,
> >
> > this effort is really good, but of course I still find things to
> > nitpick about. If there is no answer to my questions, then I would
> > prefer the documentation to spell out the unknowns and ambiguities.
> >  
> > > Cc: Pekka Paalanen <ppaalanen at gmail.com>
> > > Cc: Sebastian Wick <sebastian.wick at redhat.com>
> > > Cc: Vitaly.Prosyak at amd.com
> > > Cc: Uma Shankar <uma.shankar at intel.com>
> > > Cc: Ville Syrjälä <ville.syrjala at linux.intel.com>
> > > Cc: Joshua Ashton <joshua at froggi.es>
> > > Cc: dri-devel at lists.freedesktop.org
> > > Cc: amd-gfx at lists.freedesktop.org
> > > ---
> > >  include/drm/drm_connector.h | 67 +++++++++++++++++++++++++++++++++++--
> > >  1 file changed, 65 insertions(+), 2 deletions(-)
> > >
> > > diff --git a/include/drm/drm_connector.h b/include/drm/drm_connector.h
> > > index 6d6a53a6b010..bb078666dc34 100644
> > > --- a/include/drm/drm_connector.h
> > > +++ b/include/drm/drm_connector.h
> > > @@ -363,13 +363,76 @@ enum drm_privacy_screen_status {
> > >       PRIVACY_SCREEN_ENABLED_LOCKED,
> > >  };
> > >
> > > -/*
> > > - * This is a consolidated colorimetry list supported by HDMI and
> > > +/**
> > > + * enum drm_colorspace - color space
> > > + *
> > > + * This enum is a consolidated colorimetry list supported by HDMI and
> > >   * DP protocol standard. The respective connectors will register
> > >   * a property with the subset of this list (supported by that
> > >   * respective protocol). Userspace will set the colorspace through
> > >   * a colorspace property which will be created and exposed to
> > >   * userspace.
> > > + *
> > > + * DP definitions come from the DP v2.0 spec
> > > + * HDMI definitions come from the CTA-861-H spec
> > > + *
> > > + * @DRM_MODE_COLORIMETRY_DEFAULT:
> > > + *   Driver specific behavior.
> > > + *   For DP:
> > > + *           RGB encoded: sRGB (IEC 61966-2-1)
> > > + *           YCbCr encoded: ITU-R BT.601 colorimetry format  
> >
> > Does this mean that HDMI behavior is driver-specific while DP behavior
> > is as defined?
> >
> > Is it intentional that YCbCr encoding also uses different RGB-primaries
> > than RGB-encoded signal? (BT.601 vs. BT.709/sRGB)
> >
> > Or do you need to be more explicit on which parts of each spec apply
> > (ColourPrimaries vs. TransferCharacteristics vs. MatrixCoefficients in
> > CICP parlance)?
> >
> > E.g. BT.709/sRGB ColourPrimaries with BT.601 MatrixCoefficients.  
> 
> Yeah, just adding to this: The Default Colorspace is something well
> defined. CTA-861 says:
> 
> "If bits C0 and C1 are zero, the colorimetry shall correspond to the
> default colorimetry defined in Section 5.1"
> 
> and in Section 5.1
> 
> "In all cases described above, the RGB color space used should be the
> RGB color space the Sink declares in the Basic Display Parameters and
> Feature Block of its EDID."
> 
> If I set DRM_MODE_COLORIMETRY_DEFAULT, I expect the Colorimetry the
> EDID reports to be in effect and not some driver specific nonsense.

Does that also define the MatrixCoefficients for YCbCr signal with
DRM_MODE_COLORIMETRY_DEFAULT?

Not that userspace would even care, since RGB-to-YCbCr is all
driver-internal.

It is interesting you point that out. I guess it means that the basic
colorimetry from EDID is supposed to be really only the default
colorimetry and might not have anything to do with the actual panel
primaries.


Thanks,
pq
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