> -----Original Message-----
> From: Borah, Chaitanya Kumar <chaitanya.kumar.borah@xxxxxxxxx>
> Sent: Monday, July 10, 2023 7:13 PM
> To: intel-gfx@xxxxxxxxxxxxxxxxxxxxx
> Cc: jani.nikula@xxxxxxxxxxxxxxx; Shankar, Uma <uma.shankar@xxxxxxxxx>; Borah,
> Chaitanya Kumar <chaitanya.kumar.borah@xxxxxxxxx>
> 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@xxxxxxxxx>
> ---
> 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@xxxxxxxxx>
> + * 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
