[PATCH 4/4] drm/i915: Fix glk+ degamma LUT conversions

[Borah, Chaitanya Kumar]

> -----Original Message-----
> From: dri-devel <dri-devel-bounces at lists.freedesktop.org> On Behalf Of Ville
> Syrjala
> Sent: Friday, October 13, 2023 6:44 PM
> To: intel-gfx at lists.freedesktop.org
> Cc: dri-devel at lists.freedesktop.org
> Subject: [PATCH 4/4] drm/i915: Fix glk+ degamma LUT conversions
> 
> From: Ville Syrjälä <ville.syrjala at linux.intel.com>
> 
> The current implementation of change_lut_val_precision() is just a convoluted
> way of shifting by 8. Implement the proper rounding by just using
> drm_color_lut_extract() and intel_color_lut_pack() like everyone else does.
> 
> And as the uapi can't handle >=1.0 values but the hardware can we need to
> clamp the results appropriately in the readout path.
> 
> Signed-off-by: Ville Syrjälä <ville.syrjala at linux.intel.com>

LGTM.

Reviewed-by: Chaitanya Kumar Borah <chaitanya.kumar.borah at intel.com>


> ---
>  drivers/gpu/drm/i915/display/intel_color.c | 54 +++++++++++-----------
>  1 file changed, 28 insertions(+), 26 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/display/intel_color.c
> b/drivers/gpu/drm/i915/display/intel_color.c
> index a4b30614bd63..1cfbb3650304 100644
> --- a/drivers/gpu/drm/i915/display/intel_color.c
> +++ b/drivers/gpu/drm/i915/display/intel_color.c
> @@ -1526,14 +1526,27 @@ 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.
> - * 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)
> +static u32 glk_degamma_lut(const struct drm_color_lut *color) {
> +	return color->green;
> +}
> +
> +static void glk_degamma_lut_pack(struct drm_color_lut *entry, u32 val)
> +{
> +	/* PRE_CSC_GAMC_DATA is 3.16, clamp to 0.16 */
> +	entry->red = entry->green = entry->blue = min(val, 0xffffu); }
> +
> +static u32 mtl_degamma_lut(const struct drm_color_lut *color) {
> +	return drm_color_lut_extract(color->green, 24); }
> +
> +static void mtl_degamma_lut_pack(struct drm_color_lut *entry, u32 val)
>  {
> -	return mul_u32_u32(lut_val, (1 << to)) / (1 << from);
> +	/* PRE_CSC_GAMC_DATA is 3.24, clamp to 0.16 */
> +	entry->red = entry->green = entry->blue =
> +		intel_color_lut_pack(min(val, 0xffffffu), 24);
>  }
> 
>  static void glk_load_degamma_lut(const struct intel_crtc_state *crtc_state,
> @@ -1570,20 +1583,16 @@ 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_val);
> +			      DISPLAY_VER(i915) >= 14 ?
> +			      mtl_degamma_lut(&lut[i]) :
> glk_degamma_lut(&lut[i]));
>  	}
> 
>  	/* Clamp values > 1.0. */
>  	while (i++ < glk_degamma_lut_size(i915))
> -		ilk_lut_write(crtc_state, PRE_CSC_GAMC_DATA(pipe), 1 <<
> 16);
> +		ilk_lut_write(crtc_state, PRE_CSC_GAMC_DATA(pipe),
> +			      DISPLAY_VER(i915) >= 14 ?
> +			      1 << 24 : 1 << 16);
> 
>  	ilk_lut_write(crtc_state, PRE_CSC_GAMC_INDEX(pipe), 0);  } @@ -
> 3573,17 +3582,10 @@ static struct drm_property_blob
> *glk_read_degamma_lut(struct intel_crtc *crtc)
>  	for (i = 0; i < lut_size; i++) {
>  		u32 val = intel_de_read_fw(dev_priv,
> PRE_CSC_GAMC_DATA(pipe));
> 
> -		/*
> -		 * For MTL and beyond, convert back the 24 bit lut values
> -		 * read from HW to 16 bit values to maintain parity with
> -		 * userspace values
> -		 */
>  		if (DISPLAY_VER(dev_priv) >= 14)
> -			val = change_lut_val_precision(val, 16, 24);
> -
> -		lut[i].red = val;
> -		lut[i].green = val;
> -		lut[i].blue = val;
> +			mtl_degamma_lut_pack(&lut[i], val);
> +		else
> +			glk_degamma_lut_pack(&lut[i], val);
>  	}
> 
>  	intel_de_write_fw(dev_priv, PRE_CSC_GAMC_INDEX(pipe),
> --
> 2.41.0