AMD display drivers handling DRM CRTC color mgmt props

[Melissa Wen <mwen@igalia.com>]

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Hi all,

I'm examining how DRM color management properties (degamma, ctm, gamma)
are applied to AMD display drivers. As far I could understand thanks
Nicholas documentation on amdgpu_dm/amdgpu_dm_color, DC drivers have
per-plane color correction features:

* - Input gamma LUT (de-normalized)
* - Input CSC (normalized)
* - Surface degamma LUT (normalized)
* - Surface CSC (normalized)
* - Surface regamma LUT (normalized)
* - Output CSC (normalized)
                             
so DM is "adapting" those DRM per-CRTC properties to fit into three of
these color correction stages, which I guess are the surface stages:

* - Surface degamma LUT (normalized)
* - Surface CSC (normalized)
* - Surface regamma LUT (normalized)

I'm trying to understand what this mapping is doing. A comment mentions
that is not possible to do these color corrections after blending, so,
the same color correction pipe is performed on every plane before
blending?  (is the surface the plane?) Does this adaptation affect the
expected output?  Moreover, is there something that I misunderstood? :)

That said, if the DRM color mgmt supports per-CRTC 3D LUT as the last
step of color correction, I don't see how to accommodate it in the
mapping above, but I see DC already supports programming 3D LUT on DPP.
Once DRM has the 3D LUT interface and DM mapped it as a DPP property,
the 3D LUT will be at the end of the color correction pipeline? Is there
anything I need to worry about mapping DRM 3D LUT support? Or any
advice?

Thanks in advance,

Melissa

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