Re: [Intel-gfx] [RFC v2 03/22] drm: Add Plane Degamma Mode property

[Pekka Paalanen <ppaalanen@gmail.com>]

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On Tue,  7 Sep 2021 03:08:45 +0530
Uma Shankar <uma.shankar@intel.com> wrote:

> Add Plane Degamma Mode as an enum property. Create a helper
> function for all plane color management features.
> 
> This is an enum property with values as blob_id's and exposes
> the various gamma modes supported and the lut ranges. Getting
> the blob id in userspace, user can get the mode supported and
> also the range of gamma mode supported with number of lut
> coefficients. It can then set one of the modes using this
> enum property.
> 
> Lut values will be sent through separate GAMMA_LUT blob property.
> 
> Signed-off-by: Uma Shankar <uma.shankar@intel.com>
> ---
>  Documentation/gpu/drm-kms.rst             | 90 ++++++++++++++++++++++
>  drivers/gpu/drm/drm_atomic.c              |  1 +
>  drivers/gpu/drm/drm_atomic_state_helper.c |  2 +
>  drivers/gpu/drm/drm_atomic_uapi.c         |  4 +
>  drivers/gpu/drm/drm_color_mgmt.c          | 93 ++++++++++++++++++++++-
>  include/drm/drm_mode_object.h             |  2 +-
>  include/drm/drm_plane.h                   | 23 ++++++
>  7 files changed, 212 insertions(+), 3 deletions(-)
> 
> diff --git a/Documentation/gpu/drm-kms.rst b/Documentation/gpu/drm-kms.rst
> index 1ef7951ded5e..f4658417bf20 100644
> --- a/Documentation/gpu/drm-kms.rst
> +++ b/Documentation/gpu/drm-kms.rst
> @@ -545,9 +545,99 @@ Damage Tracking Properties
>  Color Management Properties
>  ---------------------------
>  
> +Below is how a typical hardware pipeline for color
> +will look like:
> +
> +.. kernel-render:: DOT
> +   :alt: Display Color Pipeline
> +   :caption: Display Color Pipeline Overview
> +
> +   digraph "KMS" {
> +      node [shape=box]
> +
> +      subgraph cluster_static {
> +          style=dashed
> +          label="Display Color Hardware Blocks"
> +
> +          node [bgcolor=grey style=filled]
> +          "Plane Degamma A" -> "Plane CSC/CTM A"
> +          "Plane CSC/CTM A" -> "Plane Gamma A"
> +          "Pipe Blender" [color=lightblue,style=filled, width=5.25, height=0.75];
> +          "Plane Gamma A" -> "Pipe Blender"
> +	  "Pipe Blender" -> "Pipe DeGamma"
> +          "Pipe DeGamma" -> "Pipe CSC/CTM"
> +          "Pipe CSC/CTM" -> "Pipe Gamma"
> +          "Pipe Gamma" -> "Pipe Output"
> +      }
> +
> +      subgraph cluster_static {
> +          style=dashed
> +
> +          node [shape=box]
> +          "Plane Degamma B" -> "Plane CSC/CTM B"
> +          "Plane CSC/CTM B" -> "Plane Gamma B"
> +          "Plane Gamma B" -> "Pipe Blender"
> +      }
> +
> +      subgraph cluster_static {
> +          style=dashed
> +
> +          node [shape=box]
> +          "Plane Degamma C" -> "Plane CSC/CTM C"
> +          "Plane CSC/CTM C" -> "Plane Gamma C"
> +          "Plane Gamma C" -> "Pipe Blender"
> +      }
> +
> +      subgraph cluster_fb {
> +          style=dashed
> +          label="RAM"
> +
> +          node [shape=box width=1.7 height=0.2]
> +
> +          "FB 1" -> "Plane Degamma A"
> +          "FB 2" -> "Plane Degamma B"
> +          "FB 3" -> "Plane Degamma C"
> +      }
> +   }
> +
> +In real world usecases,
> +
> +1. Plane Degamma can be used to linearize a non linear gamma
> +encoded framebuffer. This is needed to do any linear math like
> +color space conversion. For ex, linearize frames encoded in SRGB
> +or by HDR curve.

Hi,

Maybe better to avoid the term "gamma" as the curves are not always a
pure power function.

sRGB with a small s.


Thanks,
pq

> +
> +2. Later Plane CTM block can convert the content to some different
> +colorspace. For ex, SRGB to BT2020 etc.
> +
> +3. Plane Gamma block can be used later to re-apply the non-linear
> +curve. This can also be used to apply Tone Mapping for HDR usecases.
> +
> +All the layers or framebuffers need to be converted to same color
> +space and format before blending. The plane color hardware blocks
> +can help with this. Once the Data is blended, similar color processing
> +can be done on blended output using pipe color hardware blocks.
> +
> +DRM Properties have been created to define and expose all these
> +hardware blocks to userspace. A userspace application (compositor
> +or any color app) can use these interfaces and define policies to
> +efficiently use the display hardware for such color operations.
> +
> +Pipe Color Management Properties
> +---------------------------------
> +
>  .. kernel-doc:: drivers/gpu/drm/drm_color_mgmt.c
>     :doc: overview
>  
> +Plane Color Management Properties
> +---------------------------------
> +
> +.. kernel-doc:: drivers/gpu/drm/drm_color_mgmt.c
> +   :doc: Plane Color Properties
> +
> +.. kernel-doc:: drivers/gpu/drm/drm_color_mgmt.c
> +   :doc: export
> +
>  Tile Group Property
>  -------------------

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