linux-kernel - Re: [PATCH v1 3/5] drm: bridge: dw_hdmi: Enable GCP only for Deep Color

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Date:   Wed, 6 Apr 2022 11:20:16 +0200
From:   Neil Armstrong <narmstrong@...libre.com>
To:     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
Cc:     shengjiu.wang@....com, cai.huoqing@...ux.dev, maxime@...no.tech,
        harry.wentland@....com, hverkuil-cisco@...all.nl,
        amuel@...lland.org
Subject: Re: [PATCH v1 3/5] drm: bridge: dw_hdmi: Enable GCP only for Deep
 Color

On 06/04/2022 10:48, Sandor.yu@....com wrote:
> From: Sandor Yu <Sandor.yu@....com>
> 
> 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 GPC default enabled, clear gpc_auto bit for bpp 24.
> 
> Signed-off-by: Sandor Yu <Sandor.yu@....com>
> ---
>   drivers/gpu/drm/bridge/synopsys/dw-hdmi.c | 8 ++++++++
>   1 file changed, 8 insertions(+)
> 
> diff --git a/drivers/gpu/drm/bridge/synopsys/dw-hdmi.c b/drivers/gpu/drm/bridge/synopsys/dw-hdmi.c
> index b11577de4836..c7b11582529e 100644
> --- a/drivers/gpu/drm/bridge/synopsys/dw-hdmi.c
> +++ b/drivers/gpu/drm/bridge/synopsys/dw-hdmi.c
> @@ -1160,6 +1160,14 @@ 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 (color_depth == 4)
> +		/* disable Auto GCP when bpp 24 */
> +		val &= ~0x4;
> +	else
> +		val |= 0x4;
> +	hdmi_writeb(hdmi, val, HDMI_FC_DATAUTO3);
> +
>   	hdmi_modb(hdmi, HDMI_VP_STUFF_PR_STUFFING_STUFFING_MODE,
>   		  HDMI_VP_STUFF_PR_STUFFING_MASK, HDMI_VP_STUFF);
>   

Do you handle the case when color_depth == 0 when output is YUV422 ?

Neil