[RFC v2 03/22] drm: Add Plane Degamma Mode property

[Shankar, Uma]

> -----Original Message-----
> From: Pekka Paalanen <ppaalanen at gmail.com>
> Sent: Tuesday, October 12, 2021 5:20 PM
> To: Shankar, Uma <uma.shankar at intel.com>
> Cc: intel-gfx at lists.freedesktop.org; dri-devel at lists.freedesktop.org;
> harry.wentland at amd.com; ville.syrjala at linux.intel.com; brian.starkey at arm.com;
> sebastian at sebastianwick.net; Shashank.Sharma at amd.com
> Subject: Re: [RFC v2 03/22] drm: Add Plane Degamma Mode property
> 
> On Tue,  7 Sep 2021 03:08:45 +0530
> Uma Shankar <uma.shankar at 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 at 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.

Sure Pekka, will update these.

Thanks & Regards,
Uma Shankar

> 
> 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
> >  -------------------