Re: [PATCH v10 04/16] drm/mediatek: gamma: Improve and simplify HW LUT calculation

["CK Hu (胡俊光)" <ck.hu@mediatek.com>]

Hi, Angelo:

On Fri, 2023-08-04 at 09:28 +0200, AngeloGioacchino Del Regno wrote:
> Use drm_color_lut_extract() to avoid open-coding the bits reduction
> calculations for each color channel and use a struct drm_color_lut
> to temporarily store the information instead of an array of u32.
> 
> Also, slightly improve the precision of the HW LUT calculation in the
> LUT DIFF case by performing the subtractions on the 16-bits values
> and
> doing the 10 bits conversion later.
> 
> Signed-off-by: AngeloGioacchino Del Regno <
> angelogioacchino.delregno@collabora.com>
> Reviewed-by: Jason-JH.Lin <jason-jh.lin@mediatek.com>
> Reviewed-by: Alexandre Mergnat <amergnat@baylibre.com>
> ---
>  drivers/gpu/drm/mediatek/mtk_disp_gamma.c | 30 +++++++++++++++----
> ----
>  1 file changed, 20 insertions(+), 10 deletions(-)
> 
> diff --git a/drivers/gpu/drm/mediatek/mtk_disp_gamma.c
> b/drivers/gpu/drm/mediatek/mtk_disp_gamma.c
> index 7575237625d2..fd6a75a64a9f 100644
> --- a/drivers/gpu/drm/mediatek/mtk_disp_gamma.c
> +++ b/drivers/gpu/drm/mediatek/mtk_disp_gamma.c
> @@ -74,7 +74,6 @@ void mtk_gamma_set_common(struct device *dev, void
> __iomem *regs, struct drm_crt
>  	bool lut_diff;
>  	u16 lut_size;
>  	u32 word;
> -	u32 diff[3] = {0};
>  
>  	/* If there's no gamma lut there's nothing to do here. */
>  	if (!state->gamma_lut)
> @@ -97,18 +96,29 @@ void mtk_gamma_set_common(struct device *dev,
> void __iomem *regs, struct drm_crt
>  	lut_base = regs + DISP_GAMMA_LUT;
>  	lut = (struct drm_color_lut *)state->gamma_lut->data;
>  	for (i = 0; i < lut_size; i++) {
> +		struct drm_color_lut diff, hwlut;
> +
> +		hwlut.red = drm_color_lut_extract(lut[i].red, 10);
> +		hwlut.green = drm_color_lut_extract(lut[i].green, 10);
> +		hwlut.blue = drm_color_lut_extract(lut[i].blue, 10);
> +
>  		if (!lut_diff || (i % 2 == 0)) {
> -			word = (((lut[i].red >> 6) & LUT_10BIT_MASK) <<
> 20) +

After removing definition of LUT_10BIT_MASK,

Reviewed-by: CK Hu <ck.hu@mediatek.com>

> -				(((lut[i].green >> 6) & LUT_10BIT_MASK)
> << 10) +
> -				((lut[i].blue >> 6) & LUT_10BIT_MASK);
> +			word = hwlut.red << 20 +
> +			       hwlut.green << 10 +
> +			       hwlut.red;
>  		} else {
> -			diff[0] = (lut[i].red >> 6) - (lut[i - 1].red
> >> 6);
> -			diff[1] = (lut[i].green >> 6) - (lut[i -
> 1].green >> 6);
> -			diff[2] = (lut[i].blue >> 6) - (lut[i - 1].blue
> >> 6);
> +			diff.red = lut[i].red - lut[i - 1].red;
> +			diff.red = drm_color_lut_extract(diff.red, 10);
> +
> +			diff.green = lut[i].green - lut[i - 1].green;
> +			diff.green = drm_color_lut_extract(diff.green,
> 10);
> +
> +			diff.blue = lut[i].blue - lut[i - 1].blue;
> +			diff.blue = drm_color_lut_extract(diff.blue,
> 10);
>  
> -			word = ((diff[0] & LUT_10BIT_MASK) << 20) +
> -				((diff[1] & LUT_10BIT_MASK) << 10) +
> -				(diff[2] & LUT_10BIT_MASK);
> +			word = diff.blue << 20 +
> +			       diff.green << 10 +
> +			       diff.red;
>  		}
>  		writel(word, (lut_base + i * 4));
>  	}