Re: [PATCH v6 9/9] drm/mediatek: dsi: Use mipi_dsi_pixel_format_to_bpp() helper function

["CK Hu (胡俊光)" <ck.hu@mediatek.com>]

Hi, Angelo:

On Thu, 2024-02-15 at 09:53 +0100, AngeloGioacchino Del Regno wrote:
> Instead of open coding, use the mipi_dsi_pixel_format_to_bpp() helper
> function from drm_mipi_dsi.h in mtk_dsi_poweron() and for validation
> in mtk_dsi_bridge_mode_valid().
> 
> Note that this function changes the behavior of this driver:
> previously,
> in case of unknown formats, it would (wrongly) assume that it should
> account for a 24-bits format - now it will return an error and refuse
> to set clocks and/or enable the DSI.
> 
> This is done because setting the wrong data rate will only produce a
> garbage output that the display will misinterpret both because this
> driver doesn't actually provide any extra-spec format support and/or
> because the data rate (hence, the HS clock) will be wrong.

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

> 
> Reviewed-by: Alexandre Mergnat <amergnat@baylibre.com>
> Signed-off-by: AngeloGioacchino Del Regno <
> angelogioacchino.delregno@collabora.com>
> ---
>  drivers/gpu/drm/mediatek/mtk_dsi.c | 26 +++++++++-----------------
>  1 file changed, 9 insertions(+), 17 deletions(-)
> 
> diff --git a/drivers/gpu/drm/mediatek/mtk_dsi.c
> b/drivers/gpu/drm/mediatek/mtk_dsi.c
> index b644505de98a..9501f4019199 100644
> --- a/drivers/gpu/drm/mediatek/mtk_dsi.c
> +++ b/drivers/gpu/drm/mediatek/mtk_dsi.c
> @@ -598,19 +598,12 @@ static int mtk_dsi_poweron(struct mtk_dsi *dsi)
>  	if (++dsi->refcount != 1)
>  		return 0;
>  
> -	switch (dsi->format) {
> -	case MIPI_DSI_FMT_RGB565:
> -		bit_per_pixel = 16;
> -		break;
> -	case MIPI_DSI_FMT_RGB666_PACKED:
> -		bit_per_pixel = 18;
> -		break;
> -	case MIPI_DSI_FMT_RGB666:
> -	case MIPI_DSI_FMT_RGB888:
> -	default:
> -		bit_per_pixel = 24;
> -		break;
> +	ret = mipi_dsi_pixel_format_to_bpp(dsi->format);
> +	if (ret < 0) {
> +		dev_err(dev, "Unknown MIPI DSI format %d\n", dsi-
> >format);
> +		return ret;
>  	}
> +	bit_per_pixel = ret;
>  
>  	dsi->data_rate = DIV_ROUND_UP_ULL(dsi->vm.pixelclock *
> bit_per_pixel,
>  					  dsi->lanes);
> @@ -793,12 +786,11 @@ mtk_dsi_bridge_mode_valid(struct drm_bridge
> *bridge,
>  			  const struct drm_display_mode *mode)
>  {
>  	struct mtk_dsi *dsi = bridge_to_dsi(bridge);
> -	u32 bpp;
> +	int bpp;
>  
> -	if (dsi->format == MIPI_DSI_FMT_RGB565)
> -		bpp = 16;
> -	else
> -		bpp = 24;
> +	bpp = mipi_dsi_pixel_format_to_bpp(dsi->format);
> +	if (bpp < 0)
> +		return MODE_ERROR;
>  
>  	if (mode->clock * bpp / dsi->lanes > 1500000)
>  		return MODE_CLOCK_HIGH;