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

[Pekka Paalanen <ppaalanen@gmail.com>]

[-- Attachment #1: Type: text/plain, Size: 6443 bytes --]

On Tue, 7 Mar 2023 10:10:52 -0500
Harry Wentland <harry.wentland@amd.com> wrote:

> From: Joshua Ashton <joshua@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@froggi.es>
> Signed-off-by: Harry Wentland <harry.wentland@amd.com>
> Reviewed-by: Harry Wentland <harry.wentland@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@gmail.com>
> Cc: Sebastian Wick <sebastian.wick@redhat.com>
> Cc: Vitaly.Prosyak@amd.com
> Cc: Uma Shankar <uma.shankar@intel.com>
> Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
> Cc: Joshua Ashton <joshua@froggi.es>
> Cc: dri-devel@lists.freedesktop.org
> Cc: amd-gfx@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.

> + * @DRM_MODE_COLORIMETRY_NO_DATA:
> + *   Driver specific behavior.
> + *   For HDMI:
> + * 	Sets "No Data" in infoframe

Does DEFAULT mean that something else than "No Data" may be set in the
HDMI infoframe?

If so, since these two have the same value, where is the difference? Is
DEFAULT purely an UAPI token, and NO_DATA used internally? Or NO_DATA
used only when crafting actual infoframe packets?

Should NO_DATA be documented to be a strictly driver-internal value,
and not documented with UAPI?

I am unclear if userspace is using these enum values directly, or do
they use the string names only.

> + * @DRM_MODE_COLORIMETRY_SMPTE_170M_YCC:
> + *   (HDMI)
> + *   SMPTE ST 170M colorimetry format

Does "colorimetry format" mean that the spec is used in full, for all
of ColourPrimaries, TransferCharacteristics and MatrixCoefficients?

If yes, good. If not, the wording misleads me.

> + * @DRM_MODE_COLORIMETRY_BT709_YCC:
> + *   (HDMI, DP)
> + *   ITU-R BT.709 colorimetry format
> + * @DRM_MODE_COLORIMETRY_XVYCC_601:
> + *   (HDMI, DP)
> + *   xvYCC601 colorimetry format
> + * @DRM_MODE_COLORIMETRY_XVYCC_709:
> + *   (HDMI, DP)
> + *   xvYCC709 colorimetry format

Btw. xvYCC are funny because they require limited quantization range
encoding, but use the foot- and headroom to encode out-of-nominal-range
values in order to expand the color gamut with negative and greater
than unity values.

Just for curiosity, is it in any way possible today to make use of that
extended color gamut through KMS? Has it ever been possible?

I mean, the KMS color pipeline assumes full-range RGB, so I don't see
any way to make use of xvYCC.

> + * @DRM_MODE_COLORIMETRY_SYCC_601:
> + *   (HDMI, DP)
> + *   sYCC601 colorimetry format
> + * @DRM_MODE_COLORIMETRY_OPYCC_601:
> + *   (HDMI, DP)
> + *   opYCC601 colorimetry format
> + * @DRM_MODE_COLORIMETRY_OPRGB:
> + *   (HDMI, DP)
> + *   opRGB colorimetry format
> + * @DRM_MODE_COLORIMETRY_BT2020_CYCC:
> + *   (HDMI, DP)
> + *   ITU-R BT.2020 Y'c C'bc C'rc (constant luminance) colorimetry format
> + * @DRM_MODE_COLORIMETRY_BT2020_RGB:
> + *   (HDMI, DP)
> + *   ITU-R BT.2020 R' G' B' colorimetry format
> + * @DRM_MODE_COLORIMETRY_BT2020_YCC:
> + *   (HDMI, DP)
> + *   ITU-R BT.2020 Y' C'b C'r colorimetry format
> + * @DRM_MODE_COLORIMETRY_DCI_P3_RGB_D65:
> + *   (HDMI)
> + *   SMPTE ST 2113 P3D65 colorimetry format
> + * @DRM_MODE_COLORIMETRY_DCI_P3_RGB_THEATER:
> + *   (HDMI)
> + *   SMPTE ST 2113 P3DCI colorimetry format
> + * @DRM_MODE_COLORIMETRY_RGB_WIDE_FIXED:
> + *   (DP)
> + *   RGB wide gamut fixed point colorimetry format
> + * @DRM_MODE_COLORIMETRY_RGB_WIDE_FLOAT:
> + *   (DP)
> + *   RGB wide gamut floating point
> + *   (scRGB (IEC 61966-2-2)) colorimetry format

Again, there is no way to actually make use of WIDE since the KMS color
pipeline is limited to the unit range color values, right? Or is it
possible by setting all color pipeline KMS properties to pass-through
and using a floating-point FB?

I suppose the FIXED vs. FLOAT has the exact same problems as BT2020_YCC
vs. BT2020_RGB, but I would be surprised if anyone cared.

> + * @DRM_MODE_COLORIMETRY_BT601_YCC:
> + *   (DP)
> + *   ITU-R BT.601 colorimetry format
> + *   The DP spec does not say whether this is the 525 or the 625
> + *   line version.

Good to note that ambiguity here. :-)

Or maybe the DP spec writer was thinking about BT.709 ColourPrimaries
and BT.601 MatrixCoefficients...

>   */
>  enum drm_colorspace {
>  	/* For Default case, driver will set the colorspace */


Thanks,
pq

[-- Attachment #2: OpenPGP digital signature --]
[-- Type: application/pgp-signature, Size: 833 bytes --]