Re: [PATCH v15 4/7] drm/bridge: dw-hdmi: repair interworking with hdmi-connector for jz4780

[Neil Armstrong <narmstrong@baylibre.com>]

Hi,

On 12/02/2022 16:50, H. Nikolaus Schaller wrote:
> Commit 7cd70656d1285b ("drm/bridge: display-connector: implement bus fmts callbacks")
> 
> introduced a new mechanism to negotiate bus formats between hdmi connector
> and the synopsys hdmi driver inside the jz4780.
> 
> By this, the dw-hdmi is no longer the only bridge and sets up a list
> of formats in dw_hdmi_bridge_atomic_get_output_bus_fmts().
> 
> This includes MEDIA_BUS_FMT_UYVY8_1X16 which is chosen for the jz4780 but only
> produces a black screen.
> 
> This fix is based on the observation that max_bpc = 0 when running this
> function while info->bpc = 8. Since the formats checks before this always test
> for max_bpc >= info->pbc indirectly my assumption is that we must check it
> here as well.
> 
> Adding the proposed patch makes the CI20/jz4780 panel work again in
> MEDIA_BUS_FMT_RGB888_1X24 mode.
> 
> Fixes: 7cd70656d1285b ("drm/bridge: display-connector: implement bus fmts callbacks")
> Signed-off-by: H. Nikolaus Schaller <hns@goldelico.com>
> ---
>   drivers/gpu/drm/bridge/synopsys/dw-hdmi.c | 4 ++--
>   1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/gpu/drm/bridge/synopsys/dw-hdmi.c b/drivers/gpu/drm/bridge/synopsys/dw-hdmi.c
> index b0d8110dd412c..826a055a7a273 100644
> --- a/drivers/gpu/drm/bridge/synopsys/dw-hdmi.c
> +++ b/drivers/gpu/drm/bridge/synopsys/dw-hdmi.c
> @@ -2620,10 +2620,10 @@ static u32 *dw_hdmi_bridge_atomic_get_output_bus_fmts(struct drm_bridge *bridge,
>   		output_fmts[i++] = MEDIA_BUS_FMT_RGB101010_1X30;
>   	}
>   
> -	if (info->color_formats & DRM_COLOR_FORMAT_YCBCR422)
> +	if (max_bpc >= info->bpc && info->color_formats & DRM_COLOR_FORMAT_YCBCR422)
>   		output_fmts[i++] = MEDIA_BUS_FMT_UYVY8_1X16;
>   
> -	if (info->color_formats & DRM_COLOR_FORMAT_YCBCR444)
> +	if (max_bpc >= info->bpc && info->color_formats & DRM_COLOR_FORMAT_YCBCR444)
>   		output_fmts[i++] = MEDIA_BUS_FMT_YUV8_1X24;
>   
>   	/* Default 8bit RGB fallback */

Please do the same for all other cases and change the patch subject to something more accurate like:
"drm/bridge: dw-hdmi: take display info bpc in account for bus formats negociation"

Neil