Re: [PATCH v10 13/16] drm/mediatek: gamma: Program gamma LUT type for descending or rising

[CK Hu (胡俊光)]

Hi, Angelo:

On Fri, 2023-08-04 at 09:28 +0200, AngeloGioacchino Del Regno wrote:
> All of the SoCs that don't have dithering control in the gamma IP
> have got a GAMMA_LUT_TYPE bit that tells to the IP if the LUT is
> "descending" (bit set) or "rising" (bit cleared): make sure to set
> it correctly after programming the LUT.
> 
> Signed-off-by: AngeloGioacchino Del Regno <
> angelogioacchino.delregno@xxxxxxxxxxxxx>
> Reviewed-by: Jason-JH.Lin <jason-jh.lin@xxxxxxxxxxxx>
> Reviewed-by: Alexandre Mergnat <amergnat@xxxxxxxxxxxx>
> ---
>  drivers/gpu/drm/mediatek/mtk_disp_gamma.c | 20 ++++++++++++++++++++
>  1 file changed, 20 insertions(+)
> 
> diff --git a/drivers/gpu/drm/mediatek/mtk_disp_gamma.c
> b/drivers/gpu/drm/mediatek/mtk_disp_gamma.c
> index fbff9f97b737..d9a70238d524 100644
> --- a/drivers/gpu/drm/mediatek/mtk_disp_gamma.c
> +++ b/drivers/gpu/drm/mediatek/mtk_disp_gamma.c
> @@ -22,6 +22,7 @@
>  #define GAMMA_RELAY_MODE				BIT(0)
>  #define GAMMA_LUT_EN					BIT(1)
>  #define GAMMA_DITHERING					BIT(2)
> +#define GAMMA_LUT_TYPE					BIT(2)
>  #define DISP_GAMMA_SIZE				0x0030
>  #define DISP_GAMMA_SIZE_HSIZE				GENMASK
> (28, 16)
>  #define DISP_GAMMA_SIZE_VSIZE				GENMASK
> (12, 0)
> @@ -86,6 +87,17 @@ unsigned int mtk_gamma_get_lut_size(struct device
> *dev)
>  	return LUT_SIZE_DEFAULT;
>  }
>  
> +static bool mtk_gamma_lut_is_descending(struct drm_color_lut *lut,
> u32 lut_size)
> +{
> +	u64 first, last;
> +	int last_entry = lut_size - 1;
> +
> +	first = lut[0].red + lut[0].green + lut[0].blue;
> +	last = lut[last_entry].red + lut[last_entry].green +
> lut[last_entry].blue;
> +
> +	return !!(first > last);
> +}
> +
>  /*
>   * SoCs supporting 12-bits LUTs are using a new register layout that
> does
>   * always support (by HW) both 12-bits and 10-bits LUT but, on
> those, we
> @@ -175,6 +187,14 @@ void mtk_gamma_set(struct device *dev, struct
> drm_crtc_state *state)
>  		}
>  	}
>  
> +	if (!gamma->data->has_dither) {
> +		/* Descending or Rising LUT */
> +		if (mtk_gamma_lut_is_descending(lut, gamma->data-
> >lut_size - 1))
> +			cfg_val |= FIELD_PREP(GAMMA_LUT_TYPE, 1);

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

But I'm not sure why not write it more simply as

cfg_val |= GAMMA_LUT_TYPE;

Regards,
CK

> +		else
> +			cfg_val &= ~GAMMA_LUT_TYPE;
> +	}
> +
>  	/* Enable the gamma table */
>  	cfg_val |= FIELD_PREP(GAMMA_LUT_EN, 1);
>