[Intel-gfx] [PATCH v2 1/2] drm/i915/color: Upscale degamma values for MTL

[Shankar, Uma]

> -----Original Message-----
> From: Borah, Chaitanya Kumar <chaitanya.kumar.borah at intel.com>
> Sent: Monday, July 10, 2023 7:13 PM
> To: intel-gfx at lists.freedesktop.org
> Cc: jani.nikula at linux.intel.com; Shankar, Uma <uma.shankar at intel.com>; Borah,
> Chaitanya Kumar <chaitanya.kumar.borah at intel.com>
> Subject: [PATCH v2 1/2] drm/i915/color: Upscale degamma values for MTL
> 
> MTL onwards Degamma LUT/PRE-CSC LUT precision has been increased from
> 16 bits to 24 bits. Currently, drm framework only supports LUTs up to 16 bit
> precision. Until a new uapi comes along to support higher bitdepth, upscale the
> values sent from userland to 24 bit before writing into the HW to continue
> supporting degamma on MTL.
> 
> Add helper function to upscale or downscale lut values. Parameters 'to' and 'from'
> needs to be less than 32. This should be sufficient as currently there are no lut values
> exceeding 32 bit.
> 
> v2: (Jani)
>     - Reuse glk_load_degamma_lut()
>     - Create a helper function for upscaling values
> 
> Signed-off-by: Chaitanya Kumar Borah <chaitanya.kumar.borah at intel.com>
> ---
>  drivers/gpu/drm/i915/display/intel_color.c | 19 ++++++++++++++++++-
>  1 file changed, 18 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/i915/display/intel_color.c
> b/drivers/gpu/drm/i915/display/intel_color.c
> index 8966e6560516..15ada7fada96 100644
> --- a/drivers/gpu/drm/i915/display/intel_color.c
> +++ b/drivers/gpu/drm/i915/display/intel_color.c
> @@ -1453,6 +1453,16 @@ static int glk_degamma_lut_size(struct drm_i915_private
> *i915)
>  		return 35;
>  }
> 
> +/* change_lut_val_precision: helper function to upscale or downscale lut values.

Fix multi line comment style.

Change looks ok to me given the limitations of the UAPI.
Reviewed-by: Uma Shankar <uma.shankar at intel.com>

> + * Parameters 'to' and 'from' needs to be less than 32. This should be
> +sufficient
> + * as currently there are no lut values exceeding 32 bit.
> + **/
> +
> +static u32 change_lut_val_precision(u32 lut_val, int to, int from) {
> +	return mul_u32_u32(lut_val, (1 << to)) / (1 << from); }
> +
>  static void glk_load_degamma_lut(const struct intel_crtc_state *crtc_state,
>  				 const struct drm_property_blob *blob)  { @@ -
> 1487,8 +1497,15 @@ static void glk_load_degamma_lut(const struct
> intel_crtc_state *crtc_state,
>  		 * ToDo: Extend to max 7.0. Enable 32 bit input value
>  		 * as compared to just 16 to achieve this.
>  		 */
> +		u32 lut_val;
> +
> +		if (DISPLAY_VER(i915) >= 14)
> +			lut_val = change_lut_val_precision(lut[i].green, 24, 16);
> +		else
> +			lut_val = lut[i].green;
> +
>  		ilk_lut_write(crtc_state, PRE_CSC_GAMC_DATA(pipe),
> -			      lut[i].green);
> +			      lut_val);
>  	}
> 
>  	/* Clamp values > 1.0. */
> --
> 2.25.1