[RFC 02/33] drm: Add color operation structure

[Pekka Paalanen]

On Tue, 29 Aug 2023 21:33:51 +0530
Uma Shankar <uma.shankar at intel.com> wrote:

> From: Chaitanya Kumar Borah <chaitanya.kumar.borah at intel.com>
> 
> Each Color Hardware block will be represented uniquely
> in the color pipeline. Define the structure to represent
> the same.
> 
> These color operations will form the building blocks of
> a color pipeline which best represents the underlying
> Hardware. Color operations can be re-arranged, substracted
> or added to create distinct color pipelines to accurately
> describe the Hardware blocks present in the display engine.
> 
> Co-developed-by: Uma Shankar <uma.shankar at intel.com>
> Signed-off-by: Uma Shankar <uma.shankar at intel.com>
> Signed-off-by: Chaitanya Kumar Borah <chaitanya.kumar.borah at intel.com>
> ---
>  include/uapi/drm/drm_mode.h | 72 +++++++++++++++++++++++++++++++++++++
>  1 file changed, 72 insertions(+)
> 
> diff --git a/include/uapi/drm/drm_mode.h b/include/uapi/drm/drm_mode.h
> index ea1b639bcb28..882479f41745 100644
> --- a/include/uapi/drm/drm_mode.h
> +++ b/include/uapi/drm/drm_mode.h
> @@ -943,6 +943,78 @@ struct hdr_output_metadata {
>  	};
>  };
>  
> +/**
> + * enum color_op_block
> + *
> + * Enums to identify hardware color blocks.
> + *
> + * @DRM_CB_PRE_CSC: LUT before the CTM unit
> + * @DRM_CB_CSC: CTM hardware supporting 3x3 matrix
> + * @DRM_CB_POST_CSC: LUT after the CTM unit
> + * @DRM_CB_3D_LUT: LUT hardware with coefficients for all
> + *                 color components
> + * @DRM_CB_PRIVATE: Vendor specific hardware unit. Vendor
> + *                  can expose a custom hardware by defining a
> + *                  color operation block with this name as
> + *                  identifier

This naming scheme does not seem to work. It assumes a far too rigid
pipeline, just like the old KMS property design. What if you have two
other operations between PRE_CSC and CSC?

What sense do PRE_CSC and POST_CSC make if you don't happen to have a
CSC operation?

What if a driver put POST_CSC before PRE_CSC in its pipeline?

What if your CSC is actually a series of three independent operations,
and in addition you have PRE_CSC and POST_CSC?

3D_LUT is an operation category, not a name. The same could be said
about private.

Given that all these are also UAPI, do we also need protect old
userspace from seeing values it does not understand?

> + */
> +enum color_op_block {
> +	DRM_CB_INVAL = -1,
> +
> +	DRM_CB_PRE_CSC = 0,
> +	DRM_CB_CSC,
> +	DRM_CB_POST_CSC,
> +	DRM_CB_3D_LUT,
> +
> +	/* Any new generic hardware block can be updated here */
> +
> +	/*
> +	 * PRIVATE is kept at 255 to make it future proof and leave
> +	 * scope for any new addition
> +	 */
> +	DRM_CB_PRIVATE = 255,
> +	DRM_CB_MAX = DRM_CB_PRIVATE,
> +};
> +
> +/**
> + * enum color_op_type
> + *
> + * These enums are to identify the mathematical operation that
> + * a hardware block is capable of.
> + * @CURVE_1D: It represents a one dimensional lookup table
> + * @CURVE_3D: Represents lut value for each color component for 3d lut capable hardware
> + * @MATRIX: It represents co-efficients for a CSC/CTM matrix hardware
> + * @FIXED_FUNCTION: To enable and program any custom fixed function hardware unit
> + */
> +enum color_op_type {
> +	CURVE_1D,
> +	CURVE_3D,
> +	MATRIX,
> +	FIXED_FUNCTION,

My assumption was that a color_op_type would clearly and uniquely
define the mathematical model of the operation and the UABI structure
of the parameter blob. That means we need different values for uniform
vs. exponentially vs. programmable distributed 1D LUT, etc.

If there is a 1D curve with pre-programmed (fixed and named) curves, we
need to enumerate all the curve types somehow. Probably each fixed
curve type should not be a different operation type, because that would
explode the number of alternative pipelines.

A 3D curve in my mind is a function {x,y,z} = f(t), while I suspect you
meant a 3D LUT which is a {x,y,z} = f(t,u,v) - a 3-vector field in
three dimensional space.

A matrix element could be with or without an offset vector I guess.

FIXED_FUNCTION would need to be replaced with e.g. your example
VENDORXXX_BT602_TO_BT2020 to work.

Have I missed something, how did you intend this to work?


Thanks,
pq

> +};
> +
> +/**
> + * @struct drm_color_op
> + *
> + * This structure is used to represent the capability of
> + * individual color hardware blocks.
> + *
> + * @name: a standardized enum to identify the color hardware block
> + * @type: The type of mathematical operation it can perform
> + * @blob_id: Id pointing to a blob containing information about
> + *          the hardware block which advertizes its capabilities
> + *          to the userspace. It can be an optional field depending
> + *          on the members "name" and "type".
> + * @private_flags: This can be used to provide vendor specific hints
> + *                 to user space
> + */
> +struct drm_color_op {
> +	enum color_op_block name;
> +	enum color_op_type type;
> +	__u32 blob_id;
> +	__u32 private_flags;
> +};
> +
>  /**
>   * DRM_MODE_PAGE_FLIP_EVENT
>   *

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