linux-kernel - Re: [PATCH v2 26/38] drm/msm/dp: skip reading the EDID for MST cases

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Message-ID: <lusd35wv2pj5sy6mdiw7axqxnei2wqo57pf6ju5ys2ibfrkidu@63lkbckuu2n6>
Date: Mon, 9 Jun 2025 18:58:52 +0300
From: Dmitry Baryshkov <dmitry.baryshkov@....qualcomm.com>
To: Yongxing Mou <quic_yongmou@...cinc.com>
Cc: Rob Clark <robin.clark@....qualcomm.com>,
        Abhinav Kumar <abhinav.kumar@...ux.dev>,
        Jessica Zhang <jessica.zhang@....qualcomm.com>,
        Sean Paul <sean@...rly.run>,
        Marijn Suijten <marijn.suijten@...ainline.org>,
        David Airlie <airlied@...il.com>, Simona Vetter <simona@...ll.ch>,
        linux-arm-msm@...r.kernel.org, dri-devel@...ts.freedesktop.org,
        freedreno@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
        Abhinav Kumar <quic_abhinavk@...cinc.com>
Subject: Re: [PATCH v2 26/38] drm/msm/dp: skip reading the EDID for MST cases

On Mon, Jun 09, 2025 at 08:21:45PM +0800, Yongxing Mou wrote:
> From: Abhinav Kumar <quic_abhinavk@...cinc.com>
> 
> For MST cases, EDID is handled through AUX sideband messaging.
> Skip the EDID read during hotplug handle for MST cases.

Why? It makes sense to read it during the HPD processing, ping HDMI
codec, update CEC info, etc.

> 
> Signed-off-by: Abhinav Kumar <quic_abhinavk@...cinc.com>
> Signed-off-by: Yongxing Mou <quic_yongmou@...cinc.com>
> ---
>  drivers/gpu/drm/msm/dp/dp_display.c | 8 +++++---
>  1 file changed, 5 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/gpu/drm/msm/dp/dp_display.c b/drivers/gpu/drm/msm/dp/dp_display.c
> index 88cae0ca66015377e59bee757462edeae5ae91bf..b1b025d1d356046f8f9e3d243fc774185df24318 100644
> --- a/drivers/gpu/drm/msm/dp/dp_display.c
> +++ b/drivers/gpu/drm/msm/dp/dp_display.c
> @@ -438,9 +438,11 @@ static int msm_dp_display_process_hpd_high(struct msm_dp_display_private *dp)
>  	if (rc)
>  		goto end;
>  
> -	rc = msm_dp_panel_read_edid(dp->panel, connector);
> -	if (rc)
> -		goto end;
> +	if (!dp->mst_supported || !drm_dp_read_mst_cap(dp->aux, dp->panel->dpcd)) {
> +		rc = msm_dp_panel_read_edid(dp->panel, connector);
> +		if (rc)
> +			goto end;
> +	}
>  
>  	msm_dp_link_process_request(dp->link);
>  
> 
> -- 
> 2.34.1
> 

-- 
With best wishes
Dmitry