Re: [PATCH v2 1/2] media: arm: mali-c55: Add support for CCM

[Vincenzo Frascino <vincenzo.frascino@arm.com>]

Hi Jacopo,

thank you for your patch!

And sorry for the delay in my review.

On 16/06/2026 15:36, Jacopo Mondi wrote:
> From: Jacopo Mondi <jacopo.mondi+renesas@ideasonboard.com>
> 
> Add support for the CCM (Color Correction Matrix) for the Mali C55 ISP.
> 
> Define a new block in the uAPI using the extensible v4l2-isp format and
> implement support for configuring the CCM parameters in the mali-c55
> ISP driver.
> 
> Signed-off-by: Jacopo Mondi <jacopo.mondi+renesas@ideasonboard.com>

I have a couple of questions. With this:

Reviewed-by: Vincenzo Frascino <vincenzo.frascino@arm.com>

> ---
>  .../media/platform/arm/mali-c55/mali-c55-params.c  | 52 ++++++++++++++++++++++
>  include/uapi/linux/media/arm/mali-c55-config.h     | 41 ++++++++++++++++-
>  2 files changed, 92 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/media/platform/arm/mali-c55/mali-c55-params.c b/drivers/media/platform/arm/mali-c55/mali-c55-params.c
> index de0e9d898db7..96f1b28a6d77 100644
> --- a/drivers/media/platform/arm/mali-c55/mali-c55-params.c
> +++ b/drivers/media/platform/arm/mali-c55/mali-c55-params.c
> @@ -46,6 +46,7 @@
>   * @awb_config:		For header->type == MALI_C55_PARAM_BLOCK_AWB_CONFIG
>   * @shading_config:	For header->type == MALI_C55_PARAM_MESH_SHADING_CONFIG
>   * @shading_selection:	For header->type == MALI_C55_PARAM_MESH_SHADING_SELECTION
> + * @ccm:		For header->type == MALI_C55_PARAM_BLOCK_CCM
>   * @data:		Allows easy initialisation of a union variable with a
>   *			pointer into a __u8 array.
>   */
> @@ -59,6 +60,7 @@ union mali_c55_params_block {
>  	const struct mali_c55_params_awb_config *awb_config;
>  	const struct mali_c55_params_mesh_shading_config *shading_config;
>  	const struct mali_c55_params_mesh_shading_selection *shading_selection;
> +	const struct mali_c55_params_ccm *ccm;
>  	const __u8 *data;
>  };
>  
> @@ -414,6 +416,52 @@ static void mali_c55_params_lsc_selection(struct mali_c55 *mali_c55,
>  				 params->mesh_strength);
>  }
>  
> +static void mali_c55_params_ccm(struct mali_c55 *mali_c55,
> +				union mali_c55_params_block block)
> +{
> +	const struct mali_c55_params_ccm *params = block.ccm;
> +
> +	if (block.header->flags & V4L2_ISP_PARAMS_FL_BLOCK_DISABLE) {
> +		mali_c55_ctx_write(mali_c55, MALI_C55_REG_CCM_ENABLE, 0);
> +		return;
> +	}
> +
> +	mali_c55_ctx_update_bits(mali_c55, MALI_C55_REG_CCM_COEF_R_R,
> +				 MALI_C55_CCM_COEF_MASK, params->coeffs[0][0]);

Should values be validated or masked before programming? Since this is
uAPI-controlled input, it may be worth rejecting values with bits outside
MALI_C55_CCM_COEF_MASK rather than silently truncating them in update_bits().

> +	mali_c55_ctx_update_bits(mali_c55, MALI_C55_REG_CCM_COEF_R_G,
> +				 MALI_C55_CCM_COEF_MASK, params->coeffs[0][1]);
> +	mali_c55_ctx_update_bits(mali_c55, MALI_C55_REG_CCM_COEF_R_B,
> +				 MALI_C55_CCM_COEF_MASK, params->coeffs[0][2]);
> +	mali_c55_ctx_update_bits(mali_c55, MALI_C55_REG_CCM_COEF_G_R,
> +				 MALI_C55_CCM_COEF_MASK, params->coeffs[1][0]);
> +	mali_c55_ctx_update_bits(mali_c55, MALI_C55_REG_CCM_COEF_G_G,
> +				 MALI_C55_CCM_COEF_MASK, params->coeffs[1][1]);
> +	mali_c55_ctx_update_bits(mali_c55, MALI_C55_REG_CCM_COEF_G_B,
> +				 MALI_C55_CCM_COEF_MASK, params->coeffs[1][2]);
> +	mali_c55_ctx_update_bits(mali_c55, MALI_C55_REG_CCM_COEF_B_R,
> +				 MALI_C55_CCM_COEF_MASK, params->coeffs[2][0]);
> +	mali_c55_ctx_update_bits(mali_c55, MALI_C55_REG_CCM_COEF_B_G,
> +				 MALI_C55_CCM_COEF_MASK, params->coeffs[2][1]);
> +	mali_c55_ctx_update_bits(mali_c55, MALI_C55_REG_CCM_COEF_B_B,
> +				 MALI_C55_CCM_COEF_MASK, params->coeffs[2][2]);
> +
> +	mali_c55_ctx_update_bits(mali_c55, MALI_C55_REG_CCM_ANTIFOG_GAIN_R,
> +				 MALI_C55_CCM_ANTIFOG_GAIN_MASK, params->gains[0]);
> +	mali_c55_ctx_update_bits(mali_c55, MALI_C55_REG_CCM_ANTIFOG_GAIN_G,
> +				 MALI_C55_CCM_ANTIFOG_GAIN_MASK, params->gains[1]);
> +	mali_c55_ctx_update_bits(mali_c55, MALI_C55_REG_CCM_ANTIFOG_GAIN_B,
> +				 MALI_C55_CCM_ANTIFOG_GAIN_MASK, params->gains[2]);
> +
> +	mali_c55_ctx_update_bits(mali_c55, MALI_C55_REG_CCM_ANTIFOG_OFFSET_R,
> +				 MALI_C55_CCM_ANTIFOG_OFFSET_MASK, params->offs[0]);
> +	mali_c55_ctx_update_bits(mali_c55, MALI_C55_REG_CCM_ANTIFOG_OFFSET_G,
> +				 MALI_C55_CCM_ANTIFOG_OFFSET_MASK, params->offs[1]);
> +	mali_c55_ctx_update_bits(mali_c55, MALI_C55_REG_CCM_ANTIFOG_OFFSET_B,
> +				 MALI_C55_CCM_ANTIFOG_OFFSET_MASK, params->offs[2]);
> +
> +	mali_c55_ctx_write(mali_c55, MALI_C55_REG_CCM_ENABLE, 1);
> +}
> +
>  static const mali_c55_params_handler mali_c55_params_handlers[] = {
>  	[MALI_C55_PARAM_BLOCK_SENSOR_OFFS] = &mali_c55_params_sensor_offs,
>  	[MALI_C55_PARAM_BLOCK_AEXP_HIST] = &mali_c55_params_aexp_hist,
> @@ -426,6 +474,7 @@ static const mali_c55_params_handler mali_c55_params_handlers[] = {
>  	[MALI_C55_PARAM_BLOCK_AWB_GAINS_AEXP] = &mali_c55_params_awb_gains,
>  	[MALI_C55_PARAM_MESH_SHADING_CONFIG] = &mali_c55_params_lsc_config,
>  	[MALI_C55_PARAM_MESH_SHADING_SELECTION] = &mali_c55_params_lsc_selection,
> +	[MALI_C55_PARAM_BLOCK_CCM] = &mali_c55_params_ccm,
>  };
>  
>  static const struct v4l2_isp_params_block_type_info
> @@ -463,6 +512,9 @@ mali_c55_params_block_types_info[] = {
>  	[MALI_C55_PARAM_MESH_SHADING_SELECTION] = {
>  		.size = sizeof(struct mali_c55_params_mesh_shading_selection),
>  	},
> +	[MALI_C55_PARAM_BLOCK_CCM] = {
> +		.size = sizeof(struct mali_c55_params_ccm),
> +	},
>  };
>  
>  static_assert(ARRAY_SIZE(mali_c55_params_handlers) ==
> diff --git a/include/uapi/linux/media/arm/mali-c55-config.h b/include/uapi/linux/media/arm/mali-c55-config.h
> index 3d335f950eeb..0b2085eed81b 100644
> --- a/include/uapi/linux/media/arm/mali-c55-config.h
> +++ b/include/uapi/linux/media/arm/mali-c55-config.h
> @@ -219,6 +219,7 @@ struct mali_c55_stats_buffer {
>   * @MALI_C55_PARAM_BLOCK_AWB_GAINS_AEXP: Auto-white balance gains for AEXP-0 tap
>   * @MALI_C55_PARAM_MESH_SHADING_CONFIG : Mesh shading tables configuration
>   * @MALI_C55_PARAM_MESH_SHADING_SELECTION: Mesh shading table selection
> + * @MALI_C55_PARAM_BLOCK_CCM: Colour correction matrix
>   */
>  enum mali_c55_param_block_type {
>  	MALI_C55_PARAM_BLOCK_SENSOR_OFFS,
> @@ -232,6 +233,7 @@ enum mali_c55_param_block_type {
>  	MALI_C55_PARAM_BLOCK_AWB_GAINS_AEXP,
>  	MALI_C55_PARAM_MESH_SHADING_CONFIG,
>  	MALI_C55_PARAM_MESH_SHADING_SELECTION,
> +	MALI_C55_PARAM_BLOCK_CCM,
>  };
>  
>  /**
> @@ -757,6 +759,42 @@ struct mali_c55_params_mesh_shading_selection {
>  	__u16 mesh_strength;
>  };
>  
> +/**
> + * struct mali_c55_params_ccm - Coefficients, offsets and gains for the colour
> + *				correction matrix
> + *
> + * The colour correction module converts images data from a sensor-specific
> + * colour space to known one.
> + *
> + * Colour correction is applied after demosaicing and each pixel is represented
> + * as a column vector of the three RGB colour channels on which the following
> + * operations take place:
> + * 1) An offset is subtracted from each colour channel
> + * 2) Each colour channel is multiplied by a gain
> + * 3) The pixel column vector is multiplied by the colour correction matrix
> + *
> + * This struct allows users to configure the coefficients for CCM and the
> + * per-channel offsets and gains. The nine matrix coefficients are expressed as
> + * signed Q4.8 Sign/Magnitude fixed-point numbers, the three gain multipliers
> + * are expressed as unsigned Q4.8 fixed-point numbers and the three offsets are
> + * expressed as a 12-bit unsigned integers.
> + *
> + * header.type should be set to MALI_C55_PARAM_BLOCK_CCM from
> + * :c:type:`mali_c55_param_block_type`.
> + *
> + * @header:	The Mali-C55 parameters block header
> + * @coeffs:	3x3 color conversion matrix coefficients in sign/magnitude
> + *		Q4.8 format
> + * @gains:	Gains for red, green and blue channels in unsigned Q4.8 format
> + * @offs:	Offsets for red, green and blue channels
> + */
> +struct mali_c55_params_ccm {
> +	struct v4l2_isp_params_block_header header;
> +	__u16 coeffs[3][3];
> +	__u16 gains[3];
> +	__u16 offs[3];

The comment says offsets are 12-bit unsigned integers. Is there a reason why
instead of validation in the params parser so userspace gets an error for values
above 4095, we rely on register masking?

> +};
> +
>  /**
>   * define MALI_C55_PARAMS_MAX_SIZE - Maximum size of all Mali C55 Parameters
>   *
> @@ -780,6 +818,7 @@ struct mali_c55_params_mesh_shading_selection {
>  	sizeof(struct mali_c55_params_awb_config) +		\
>  	sizeof(struct mali_c55_params_awb_gains) +		\
>  	sizeof(struct mali_c55_params_mesh_shading_config) +	\
> -	sizeof(struct mali_c55_params_mesh_shading_selection))
> +	sizeof(struct mali_c55_params_mesh_shading_selection) +	\
> +	sizeof(struct mali_c55_params_ccm))
>  
>  #endif /* __UAPI_MALI_C55_CONFIG_H */
> 

-- 
Regards,
Vincenzo