[PATCH v2 3/4] drm: lcdif: Switch to limited range for RGB to YUV conversion

[Kieran Bingham]

Quoting Laurent Pinchart (2022-09-28 01:58:11)
> Up to and including v1.3, HDMI supported limited quantization range only
> for YCbCr. HDMI v1.4 introduced selectable quantization ranges, but this
> features isn't supported in the dw-hdmi driver that is used in
> conjunction with the LCDIF in the i.MX8MP. The HDMI YCbCr output is thus
> always advertised in the AVI infoframe as limited range.
> 
> The LCDIF driver, on the other hand, configures the CSC to produce full
> range YCbCr. This mismatch results in loss of details and incorrect
> colours. Fix it by switching to limited range YCbCr.
> 
> The coefficients are copied from drivers/media/platforms/nxp/imx-pxp.c
> for coherency, as the hardware is most likely identical.

Perhaps we need one or two of these somewhere:

https://colorconfidence.com/products/calibrite-colorchecker-display

Or does anyone have one that could test this patch?

Anyway:

Reviewed-by: Kieran Bingham <kieran.bingham at ideasonboard.com>


> Fixes: 9db35bb349a0 ("drm: lcdif: Add support for i.MX8MP LCDIF variant")
> Signed-off-by: Laurent Pinchart <laurent.pinchart at ideasonboard.com>
> ---
> Changes since v1:
> 
> - Use coefficients from imx-pxp.c
> ---
>  drivers/gpu/drm/mxsfb/lcdif_kms.c | 12 ++++++------
>  1 file changed, 6 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/gpu/drm/mxsfb/lcdif_kms.c b/drivers/gpu/drm/mxsfb/lcdif_kms.c
> index 1f22ea5896d5..c3622be0c587 100644
> --- a/drivers/gpu/drm/mxsfb/lcdif_kms.c
> +++ b/drivers/gpu/drm/mxsfb/lcdif_kms.c
> @@ -53,16 +53,16 @@ static void lcdif_set_formats(struct lcdif_drm_private *lcdif,
>                 writel(DISP_PARA_LINE_PATTERN_UYVY_H,
>                        lcdif->base + LCDC_V8_DISP_PARA);
>  
> -               /* CSC: BT.601 Full Range RGB to YCbCr coefficients. */
> -               writel(CSC0_COEF0_A2(0x096) | CSC0_COEF0_A1(0x04c),
> +               /* CSC: BT.601 Limited Range RGB to YCbCr coefficients. */
> +               writel(CSC0_COEF0_A2(0x081) | CSC0_COEF0_A1(0x041),
>                        lcdif->base + LCDC_V8_CSC0_COEF0);
> -               writel(CSC0_COEF1_B1(0x7d5) | CSC0_COEF1_A3(0x01d),
> +               writel(CSC0_COEF1_B1(0x7db) | CSC0_COEF1_A3(0x019),
>                        lcdif->base + LCDC_V8_CSC0_COEF1);
> -               writel(CSC0_COEF2_B3(0x080) | CSC0_COEF2_B2(0x7ac),
> +               writel(CSC0_COEF2_B3(0x070) | CSC0_COEF2_B2(0x7b6),
>                        lcdif->base + LCDC_V8_CSC0_COEF2);
> -               writel(CSC0_COEF3_C2(0x795) | CSC0_COEF3_C1(0x080),
> +               writel(CSC0_COEF3_C2(0x7a2) | CSC0_COEF3_C1(0x070),
>                        lcdif->base + LCDC_V8_CSC0_COEF3);
> -               writel(CSC0_COEF4_D1(0x000) | CSC0_COEF4_C3(0x7ec),
> +               writel(CSC0_COEF4_D1(0x010) | CSC0_COEF4_C3(0x7ee),
>                        lcdif->base + LCDC_V8_CSC0_COEF4);
>                 writel(CSC0_COEF5_D3(0x080) | CSC0_COEF5_D2(0x080),
>                        lcdif->base + LCDC_V8_CSC0_COEF5);
> -- 
> Regards,
> 
> Laurent Pinchart
>