[RFC 0/1] Color space conversion uapi part2

[Alexandru Gheorghe]

This is an attempt to revive the color space conversation that started
here [1] and was materialized with the color encoding and color range
properties for converting YUV2RGB, the last version of this patch
series is here [2].

However, we still need a way of specifing the color gamut and transfer
function(gamma) for a given plane, in order to be sure that the
blending is done in the same domain space, which is not an issue for
similar gammuts, but not so good when mixing wider gamuts like Rec2020
and DCI-P3 with narrow ones.

In consequence, the userspace needs to control what is the color gamut
used for blending.

On Mali DP hardware, a complete color processing pipeline for a plane
looks like this:

YUV2RGB -> DEGAMA -> RGB2RGB(Gammut conv) -> GAMMA.

Of course, depending on hardware generation some of this elements are
not present or disabled if we are dealing with a RGB buffer already
in linear space. But it's up to the usperspace to decide what it wants
when the hardware doesn't provide full support for its needs.

What this patchset proposes is to add plane degamma, ctm and gamma
properties to be applied in this order after the yuv2rgb conversion
specified by the color encoding property[2]. We already have this sort
of pipeline(degamma, ctm, gamma) at the other end of a CRTC, so it
wouldn't be a totaly new interface for userspaces to figure it out how
to use.

There are still some things to be done before getting this patchset in
mergeable shape like: mali-dp driver implementation, real userspace
(drm_hwcomposer is the likely candidate here, but I'm open to
suggestions here), reuse some of the code for both crtc and plane.

But first, I would like to see what everybody things about this idea,
or if it has a different perspective of how this should be handled.

[1] https://lkml.org/lkml/2017/3/16/681
[2] https://www.spinics.net/lists/intel-gfx/msg156211.html

Mihail Atanassov (1):
  drm: Add per-plane color management

 drivers/gpu/drm/drm_atomic.c        | 28 ++++++++++++++
 drivers/gpu/drm/drm_atomic_helper.c |  9 +++++
 drivers/gpu/drm/drm_color_mgmt.c    | 76 +++++++++++++++++++++++++++----------
 include/drm/drm_color_mgmt.h        |  5 +++
 include/drm/drm_mode_config.h       | 20 +++++-----
 include/drm/drm_plane.h             |  8 ++++
 6 files changed, 117 insertions(+), 29 deletions(-)

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2.7.4