linux-kernel - Re: [PATCH v6 3/7] drm/edid: MSO should only be used for non-eDP displays

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Message-ID: <5be6faede273533b88e592bd25776b639d2eeb9f@intel.com>
Date: Wed, 26 Nov 2025 16:10:34 +0200
From: Jani Nikula <jani.nikula@...ux.intel.com>
To: Yaroslav Bolyukin <iam@...h.pw>, Ville Syrjälä
 <ville.syrjala@...ux.intel.com>, Maarten Lankhorst
 <maarten.lankhorst@...ux.intel.com>, Maxime Ripard <mripard@...nel.org>,
 Thomas Zimmermann <tzimmermann@...e.de>, David Airlie <airlied@...il.com>,
 Simona Vetter <simona@...ll.ch>
Cc: Harry Wentland <harry.wentland@....com>, Leo Li <sunpeng.li@....com>,
 Rodrigo Siqueira <siqueira@...lia.com>, Alex Deucher
 <alexander.deucher@....com>, Christian König
 <christian.koenig@....com>,
 Wayne Lin <Wayne.Lin@....com>, amd-gfx@...ts.freedesktop.org,
 linux-kernel@...r.kernel.org, dri-devel@...ts.freedesktop.org, Yaroslav
 Bolyukin <iam@...h.pw>
Subject: Re: [PATCH v6 3/7] drm/edid: MSO should only be used for non-eDP
 displays

On Wed, 26 Nov 2025, Yaroslav Bolyukin <iam@...h.pw> wrote:
> As per DisplayID v2.1a spec:
> If Offset 06h[2:0] is programmed to 001b (External DisplayPort), this
> field shall be cleared to 00b (Not supported).
>
> Link: https://lore.kernel.org/lkml/3abc1087618c822e5676e67a3ec2e64e506dc5ec@intel.com/
> Signed-off-by: Yaroslav Bolyukin <iam@...h.pw>
> ---
>  drivers/gpu/drm/drm_displayid_internal.h |  4 +++
>  drivers/gpu/drm/drm_edid.c               | 36 +++++++++++++++---------
>  2 files changed, 27 insertions(+), 13 deletions(-)
>
> diff --git a/drivers/gpu/drm/drm_displayid_internal.h b/drivers/gpu/drm/drm_displayid_internal.h
> index 5b1b32f73516..72f107ae832f 100644
> --- a/drivers/gpu/drm/drm_displayid_internal.h
> +++ b/drivers/gpu/drm/drm_displayid_internal.h
> @@ -142,9 +142,13 @@ struct displayid_formula_timing_block {
>  	struct displayid_formula_timings_9 timings[];
>  } __packed;
>  
> +#define DISPLAYID_VESA_DP_TYPE		GENMASK(2, 0)
>  #define DISPLAYID_VESA_MSO_OVERLAP	GENMASK(3, 0)
>  #define DISPLAYID_VESA_MSO_MODE		GENMASK(6, 5)
>  
> +#define DISPLAYID_VESA_DP_TYPE_EDP	0
> +#define DISPLAYID_VESA_DP_TYPE_DP	1
> +
>  struct displayid_vesa_vendor_specific_block {
>  	struct displayid_block base;
>  	u8 oui[3];
> diff --git a/drivers/gpu/drm/drm_edid.c b/drivers/gpu/drm/drm_edid.c
> index a52fd6de9327..348aa31aea1b 100644
> --- a/drivers/gpu/drm/drm_edid.c
> +++ b/drivers/gpu/drm/drm_edid.c
> @@ -6533,6 +6533,7 @@ static void drm_parse_vesa_specific_block(struct drm_connector *connector,
>  	struct displayid_vesa_vendor_specific_block *vesa =
>  		(struct displayid_vesa_vendor_specific_block *)block;
>  	struct drm_display_info *info = &connector->display_info;
> +	int dp_type;
>  
>  	if (block->num_bytes < 3) {
>  		drm_dbg_kms(connector->dev,
> @@ -6551,20 +6552,29 @@ static void drm_parse_vesa_specific_block(struct drm_connector *connector,
>  		return;
>  	}
>  
> -	switch (FIELD_GET(DISPLAYID_VESA_MSO_MODE, vesa->mso)) {
> -	default:
> -		drm_dbg_kms(connector->dev, "[CONNECTOR:%d:%s] Reserved MSO mode value\n",
> +	dp_type = FIELD_GET(DISPLAYID_VESA_DP_TYPE, vesa->data_structure_type);
> +	if (dp_type > 1) {
> +		drm_dbg_kms(connector->dev, "[CONNECTOR:%d:%s] Reserved dp type value\n",
>  			    connector->base.id, connector->name);
> -		fallthrough;
> -	case 0:
> -		info->mso_stream_count = 0;
> -		break;
> -	case 1:
> -		info->mso_stream_count = 2; /* 2 or 4 links */
> -		break;
> -	case 2:
> -		info->mso_stream_count = 4; /* 4 links */
> -		break;
> +	}
> +
> +	/* MSO is not supported for eDP */
> +	if (dp_type != DISPLAYID_VESA_DP_TYPE_EDP) {

MSO is *only* supported on eDP, not the other way round!

BR,
Jani.

> +		switch (FIELD_GET(DISPLAYID_VESA_MSO_MODE, vesa->mso)) {
> +		default:
> +			drm_dbg_kms(connector->dev, "[CONNECTOR:%d:%s] Reserved MSO mode value\n",
> +				    connector->base.id, connector->name);
> +			fallthrough;
> +		case 0:
> +			info->mso_stream_count = 0;
> +			break;
> +		case 1:
> +			info->mso_stream_count = 2; /* 2 or 4 links */
> +			break;
> +		case 2:
> +			info->mso_stream_count = 4; /* 4 links */
> +			break;
> +		}
>  	}
>  
>  	if (info->mso_stream_count) {

-- 
Jani Nikula, Intel