linux-kernel - Re: [PATCH v2 3/5] drm: bridge: dw_hdmi: Enable GCP only for Deep Color

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Message-ID: <25ca3826-44ee-ca6f-fb6b-1ef62f6da456@baylibre.com>
Date:   Fri, 8 Apr 2022 14:40:23 +0200
From:   Neil Armstrong <narmstrong@...libre.com>
To:     Sandor Yu <Sandor.yu@....com>, dri-devel@...ts.freedesktop.org,
        linux-kernel@...r.kernel.org, andrzej.hajda@...el.com,
        robert.foss@...aro.org, Laurent.pinchart@...asonboard.com,
        jonas@...boo.se, jernej.skrabec@...il.com, hverkuil-cisco@...all.nl
Cc:     shengjiu.wang@....com, cai.huoqing@...ux.dev, maxime@...no.tech,
        harry.wentland@....com
Subject: Re: [PATCH v2 3/5] drm: bridge: dw_hdmi: Enable GCP only for Deep
 Color

On 08/04/2022 12:32, Sandor Yu wrote:
> HDMI1.4b specification section 6.5.3:
> Source shall only send GCPs with non-zero CD to sinks
> that indicate support for Deep Color.
> 
> DW HDMI GCP default enabled, clear gpc_auto bit for 24-bit color depth.

It's right because we do not handle AVMUTE, Pixel Packing nor Default_Phase.

> 
> Signed-off-by: Sandor Yu <Sandor.yu@....com>
> ---
>   drivers/gpu/drm/bridge/synopsys/dw-hdmi.c | 12 ++++++++++++
>   1 file changed, 12 insertions(+)
> 
> diff --git a/drivers/gpu/drm/bridge/synopsys/dw-hdmi.c b/drivers/gpu/drm/bridge/synopsys/dw-hdmi.c
> index 02d8f7e08814..5a7ec066e37a 100644
> --- a/drivers/gpu/drm/bridge/synopsys/dw-hdmi.c
> +++ b/drivers/gpu/drm/bridge/synopsys/dw-hdmi.c
> @@ -1108,6 +1108,8 @@ static void hdmi_video_packetize(struct dw_hdmi *hdmi)
>   	unsigned int output_select = HDMI_VP_CONF_OUTPUT_SELECTOR_PP;
>   	struct hdmi_data_info *hdmi_data = &hdmi->hdmi_data;
>   	u8 val, vp_conf;
> +	u8 clear_gcp_auto = 0;
> +
>   
>   	if (hdmi_bus_fmt_is_rgb(hdmi->hdmi_data.enc_out_bus_format) ||
>   	    hdmi_bus_fmt_is_yuv444(hdmi->hdmi_data.enc_out_bus_format) ||
> @@ -1117,6 +1119,7 @@ static void hdmi_video_packetize(struct dw_hdmi *hdmi)
>   		case 8:
>   			color_depth = 4;
>   			output_select = HDMI_VP_CONF_OUTPUT_SELECTOR_BYPASS;
> +			clear_gcp_auto = 1;
>   			break;
>   		case 10:
>   			color_depth = 5;
> @@ -1136,6 +1139,7 @@ static void hdmi_video_packetize(struct dw_hdmi *hdmi)
>   		case 0:
>   		case 8:
>   			remap_size = HDMI_VP_REMAP_YCC422_16bit;
> +			clear_gcp_auto = 1;
>   			break;
>   		case 10:
>   			remap_size = HDMI_VP_REMAP_YCC422_20bit;
> @@ -1160,6 +1164,14 @@ static void hdmi_video_packetize(struct dw_hdmi *hdmi)
>   		HDMI_VP_PR_CD_DESIRED_PR_FACTOR_MASK);
>   	hdmi_writeb(hdmi, val, HDMI_VP_PR_CD);
>   
> +	val = hdmi_readb(hdmi, HDMI_FC_DATAUTO3);
> +	if (clear_gcp_auto == 1)
> +		/* disable Auto GCP when 24-bit color */

Maybe add a new define for HDMI_FC_DATAUTO3_GCP_AUTO bit and use it here.

> +		val &= ~0x4;
> +	else
> +		val |= 0x4;
> +	hdmi_writeb(hdmi, val, HDMI_FC_DATAUTO3);

Please also add a comment explaining we clear GCP because we only
transmit CD and do not handle AVMUTE, PP nor Default_Phase (yet).

> +
>   	hdmi_modb(hdmi, HDMI_VP_STUFF_PR_STUFFING_STUFFING_MODE,
>   		  HDMI_VP_STUFF_PR_STUFFING_MASK, HDMI_VP_STUFF);
>   

Thanks,
Neil