Re: [PATCH 1/4] Documentation/amdgpu_dm: Add DM color correction documentation

[Tales Lelo da Aparecida <tales.aparecida@gmail.com>]

On 16/07/2022 19:25, Melissa Wen wrote:
> AMDGPU DM maps DRM color management properties (degamma, ctm and gamma)
> to DC color correction entities. Part of this mapping is already
> documented as code comments and can be converted as kernel docs.
> 
> v2:
> - rebase to amd-staging-drm-next
> 
> Reviewed-by: Harry Wentland <harry.wentland@amd.com>
> Signed-off-by: Melissa Wen <mwen@igalia.com>
> ---
>   .../gpu/amdgpu/display/display-manager.rst    |   9 ++
>   .../amd/display/amdgpu_dm/amdgpu_dm_color.c   | 121 +++++++++++++-----
>   2 files changed, 98 insertions(+), 32 deletions(-)
> 
> diff --git a/Documentation/gpu/amdgpu/display/display-manager.rst b/Documentation/gpu/amdgpu/display/display-manager.rst
> index 7ce31f89d9a0..b1b0f11aed83 100644
> --- a/Documentation/gpu/amdgpu/display/display-manager.rst
> +++ b/Documentation/gpu/amdgpu/display/display-manager.rst
> @@ -40,3 +40,12 @@ Atomic Implementation
>   
>   .. kernel-doc:: drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
>      :functions: amdgpu_dm_atomic_check amdgpu_dm_atomic_commit_tail
> +
> +Color Management Properties
> +===========================
> +
> +.. kernel-doc:: drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_color.c
> +   :doc: overview
> +
> +.. kernel-doc:: drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_color.c
> +   :internal:
> diff --git a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_color.c b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_color.c
> index a71177305bcd..93c813089bff 100644
> --- a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_color.c
> +++ b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_color.c
> @@ -29,7 +29,9 @@
>   #include "modules/color/color_gamma.h"
>   #include "basics/conversion.h"
>   
> -/*
> +/**
> + * DOC: overview
> + *
>    * The DC interface to HW gives us the following color management blocks
>    * per pipe (surface):
>    *
> @@ -71,8 +73,8 @@
>   
>   #define MAX_DRM_LUT_VALUE 0xFFFF
>   
> -/*
> - * Initialize the color module.
> +/**
> + * amdgpu_dm_init_color_mod - Initialize the color module.
>    *
>    * We're not using the full color module, only certain components.
>    * Only call setup functions for components that we need.
> @@ -82,7 +84,14 @@ void amdgpu_dm_init_color_mod(void)
>   	setup_x_points_distribution();
>   }
>   
> -/* Extracts the DRM lut and lut size from a blob. */
> +/**
> + * __extract_blob_lut - Extracts the DRM lut and lut size from a blob.
> + * @blob: DRM color mgmt property blob
> + * @size: lut size
> + *
> + * Returns:
> + * DRM LUT or NULL
> + */
>   static const struct drm_color_lut *
>   __extract_blob_lut(const struct drm_property_blob *blob, uint32_t *size)
>   {
> @@ -90,13 +99,18 @@ __extract_blob_lut(const struct drm_property_blob *blob, uint32_t *size)
>   	return blob ? (struct drm_color_lut *)blob->data : NULL;
>   }

I don't think everyone would approve using actual kernel-doc for these 
static functions, but I can appreciate they being formatted as such.
Consider replacing /** with /*.

> -/*
> - * Return true if the given lut is a linear mapping of values, i.e. it acts
> - * like a bypass LUT.
> +/**
> + * __is_lut_linear - check if the given lut is a linear mapping of values
> + * @lut: given lut to check values
> + * @size: lut size
>    *
>    * It is considered linear if the lut represents:
> - * f(a) = (0xFF00/MAX_COLOR_LUT_ENTRIES-1)a; for integer a in
> - *                                           [0, MAX_COLOR_LUT_ENTRIES)
> + * f(a) = (0xFF00/MAX_COLOR_LUT_ENTRIES-1)a; for integer a in [0,
> + * MAX_COLOR_LUT_ENTRIES)
> + *
> + * Returns:
> + * True if the given lut is a linear mapping of values, i.e. it acts like a
> + * bypass LUT. Otherwise, false.
>    */
>   static bool __is_lut_linear(const struct drm_color_lut *lut, uint32_t size)
>   {
> @@ -119,9 +133,13 @@ static bool __is_lut_linear(const struct drm_color_lut *lut, uint32_t size)
>   	return true;
>   }
>   
> -/*
> - * Convert the drm_color_lut to dc_gamma. The conversion depends on the size
> - * of the lut - whether or not it's legacy.
> +/**
> + * __drm_lut_to_dc_gamma - convert the drm_color_lut to dc_gamma.
> + * @lut: DRM lookup table for color conversion
> + * @gamma: DC gamma to set entries
> + * @is_legacy: legacy or atomic gamma
> + *
> + * The conversion depends on the size of the lut - whether or not it's legacy.
>    */
>   static void __drm_lut_to_dc_gamma(const struct drm_color_lut *lut,
>   				  struct dc_gamma *gamma, bool is_legacy)
> @@ -154,8 +172,11 @@ static void __drm_lut_to_dc_gamma(const struct drm_color_lut *lut,
>   	}
>   }
>   
> -/*
> - * Converts a DRM CTM to a DC CSC float matrix.
> +/**
> + * __drm_ctm_to_dc_matrix - converts a DRM CTM to a DC CSC float matrix
> + * @ctm: DRM color transformation matrix
> + * @matrix: DC CSC float matrix
> + *
>    * The matrix needs to be a 3x4 (12 entry) matrix.
>    */
>   static void __drm_ctm_to_dc_matrix(const struct drm_color_ctm *ctm,
> @@ -189,7 +210,18 @@ static void __drm_ctm_to_dc_matrix(const struct drm_color_ctm *ctm,
>   	}
>   }
>   
> -/* Calculates the legacy transfer function - only for sRGB input space. */
> +/**
> + * __set_legacy_tf - Calculates the legacy transfer function
> + * @func: transfer function
> + * @lut: lookup table that defines the color space
> + * @lut_size: size of respective lut
> + * @has_rom: if ROM can be used for hardcoded curve
> + *
> + * Only for sRGB input space
> + *
> + * Returns:
> + * 0 in case of sucess, -ENOMEM if fails

Typo sucess -> success

> + */
>   static int __set_legacy_tf(struct dc_transfer_func *func,
>   			   const struct drm_color_lut *lut, uint32_t lut_size,
>   			   bool has_rom)
> @@ -218,7 +250,16 @@ static int __set_legacy_tf(struct dc_transfer_func *func,
>   	return res ? 0 : -ENOMEM;
>   }
>   
> -/* Calculates the output transfer function based on expected input space. */
> +/**
> + * __set_output_tf - calculates the output transfer function based on expected input space.
> + * @func: transfer function
> + * @lut: lookup table that defines the color space
> + * @lut_size: size of respective lut
> + * @has_rom: if ROM can be used for hardcoded curve
> + *
> + * Returns:
> + * 0 in case of success. -ENOMEM if fails.
> + */
>   static int __set_output_tf(struct dc_transfer_func *func,
>   			   const struct drm_color_lut *lut, uint32_t lut_size,
>   			   bool has_rom)
> @@ -239,7 +280,7 @@ static int __set_output_tf(struct dc_transfer_func *func,
>   	__drm_lut_to_dc_gamma(lut, gamma, false);
>   
>   	if (func->tf == TRANSFER_FUNCTION_LINEAR) {
> -		/*
> +		/**

I don't think kernel-doc should be used inside functions, as well,
maybe keep the "/*" from before. This occurs in more places in this 
patch, remember to replace them as well, if you concur.

>   		 * Color module doesn't like calculating regamma params
>   		 * on top of a linear input. But degamma params can be used
>   		 * instead to simulate this.
> @@ -262,7 +303,16 @@ static int __set_output_tf(struct dc_transfer_func *func,
>   	return res ? 0 : -ENOMEM;
>   }
>   
> -/* Caculates the input transfer function based on expected input space. */
> +/**
> + * __set_input_tf - calculates the input transfer function based on expected
> + * input space.
> + * @func: transfer function
> + * @lut: lookup table that defines the color space
> + * @lut_size: size of respective lut.
> + *
> + * Returns:
> + * 0 in case of success. -ENOMEM if fails.
> + */
>   static int __set_input_tf(struct dc_transfer_func *func,
>   			  const struct drm_color_lut *lut, uint32_t lut_size)
>   {
> @@ -285,13 +335,15 @@ static int __set_input_tf(struct dc_transfer_func *func,
>   }
>   
>   /**
> - * amdgpu_dm_verify_lut_sizes
> + * amdgpu_dm_verify_lut_sizes - verifies if DRM luts match the hw supported sizes
>    * @crtc_state: the DRM CRTC state
>    *
> - * Verifies that the Degamma and Gamma LUTs attached to the |crtc_state| are of
> - * the expected size.
> + * Verifies that the Degamma and Gamma LUTs attached to the &crtc_state
> + * are of the expected size.
>    *
> - * Returns 0 on success.
> + * Returns:
> + * 0 on success.
> + * -EINVAL if any lut sizes are invalid.

I don't know if you expect this to be rendered in two lines, given that 
you wrote something equivalent in a single line in other docstrings 
above, but if you do, use instead:
```
* * 0 on success.
* * -EINVAL if any lut sizes are invalid.
```
As described at: 
https://www.kernel.org/doc/html/latest/doc-guide/kernel-doc.html#return-values

>    */
>   int amdgpu_dm_verify_lut_sizes(const struct drm_crtc_state *crtc_state)
>   {
> @@ -327,9 +379,9 @@ int amdgpu_dm_verify_lut_sizes(const struct drm_crtc_state *crtc_state)
>    * of the HW blocks as long as the CRTC CTM always comes before the
>    * CRTC RGM and after the CRTC DGM.
>    *
> - * The CRTC RGM block will be placed in the RGM LUT block if it is non-linear.
> - * The CRTC DGM block will be placed in the DGM LUT block if it is non-linear.
> - * The CRTC CTM will be placed in the gamut remap block if it is non-linear.
> + * * The CRTC RGM block will be placed in the RGM LUT block if it is non-linear.
> + * * The CRTC DGM block will be placed in the DGM LUT block if it is non-linear.
> + * * The CRTC CTM will be placed in the gamut remap block if it is non-linear.
>    *
>    * The RGM block is typically more fully featured and accurate across
>    * all ASICs - DCE can't support a custom non-linear CRTC DGM.
> @@ -338,7 +390,9 @@ int amdgpu_dm_verify_lut_sizes(const struct drm_crtc_state *crtc_state)
>    * management at once we have to either restrict the usage of CRTC properties
>    * or blend adjustments together.
>    *
> - * Returns 0 on success.
> + * Returns:
> + * 0 on success.
> + * Error code if setup fails.
>    */
>   int amdgpu_dm_update_crtc_color_mgmt(struct dm_crtc_state *crtc)
>   {
> @@ -373,7 +427,7 @@ int amdgpu_dm_update_crtc_color_mgmt(struct dm_crtc_state *crtc)
>   
>   	/* Setup regamma and degamma. */
>   	if (is_legacy) {
> -		/*
> +		/**
>   		 * Legacy regamma forces us to use the sRGB RGM as a base.
>   		 * This also means we can't use linear DGM since DGM needs
>   		 * to use sRGB as a base as well, resulting in incorrect CRTC
> @@ -393,7 +447,8 @@ int amdgpu_dm_update_crtc_color_mgmt(struct dm_crtc_state *crtc)
>   		if (r)
>   			return r;
>   	} else if (has_regamma) {
> -		/* CRTC RGM goes into RGM LUT. */
> +		/**
> +		 * If atomic regamma, CRTC RGM goes into RGM LUT. */
>   		stream->out_transfer_func->type = TF_TYPE_DISTRIBUTED_POINTS;
>   		stream->out_transfer_func->tf = TRANSFER_FUNCTION_LINEAR;
>   
> @@ -402,7 +457,7 @@ int amdgpu_dm_update_crtc_color_mgmt(struct dm_crtc_state *crtc)
>   		if (r)
>   			return r;
>   	} else {
> -		/*
> +		/**
>   		 * No CRTC RGM means we can just put the block into bypass
>   		 * since we don't have any plane level adjustments using it.
>   		 */
> @@ -410,7 +465,7 @@ int amdgpu_dm_update_crtc_color_mgmt(struct dm_crtc_state *crtc)
>   		stream->out_transfer_func->tf = TRANSFER_FUNCTION_LINEAR;
>   	}
>   
> -	/*
> +	/**
>   	 * CRTC DGM goes into DGM LUT. It would be nice to place it
>   	 * into the RGM since it's a more featured block but we'd
>   	 * have to place the CTM in the OCSC in that case.
> @@ -421,7 +476,7 @@ int amdgpu_dm_update_crtc_color_mgmt(struct dm_crtc_state *crtc)
>   	if (crtc->base.ctm) {
>   		ctm = (struct drm_color_ctm *)crtc->base.ctm->data;
>   
> -		/*
> +		/**
>   		 * Gamut remapping must be used for gamma correction
>   		 * since it comes before the regamma correction.
>   		 *
> @@ -452,7 +507,9 @@ int amdgpu_dm_update_crtc_color_mgmt(struct dm_crtc_state *crtc)
>    * preparation for hardware commit. The transfer function used depends on
>    * the prepartion done on the stream for color management.

Could you fix this typo while you are here? prepartion -> preparation

>    *
> - * Returns 0 on success.
> + * Returns:
> + * 0 on success.
> + * ENOMEM if mem allocation fails.
>    */
>   int amdgpu_dm_update_plane_color_mgmt(struct dm_crtc_state *crtc,
>   				      struct dc_plane_state *dc_plane_state)

Thanks for creating more documentation!

Kind regards,
Tales