linux-kernel - Re: [PATCH v6 2/7] drm/edid: prepare for VESA vendor-specific data block extension

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Message-ID: <b7191ab7c3030a8be0b149d28ae6fa032b64a4d8@intel.com>
Date: Wed, 26 Nov 2025 16:08:20 +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 2/7] drm/edid: prepare for VESA vendor-specific data
 block extension

On Wed, 26 Nov 2025, Jani Nikula <jani.nikula@...ux.intel.com> wrote:
> On Wed, 26 Nov 2025, Yaroslav Bolyukin <iam@...h.pw> wrote:
>> Current VESA vendor-specific block parsing expects real block size to be
>> the same as the defined struct size, use real offsets in conditionals
>> instead to add struct fields in future commits.
>>
>> Signed-off-by: Yaroslav Bolyukin <iam@...h.pw>
>
> I think this is something we want to backport, since MSO would break
> with bigger vendor-specific blocks, and that leads to black screens on
> MSO displays.
>
> Cc: stable@...r.kernel.org
> Reviewed-by: Jani Nikula <jani.nikula@...el.com>

Oops, I'll take that back.

>
>> ---
>>  drivers/gpu/drm/drm_edid.c | 28 ++++++++++++----------------
>>  1 file changed, 12 insertions(+), 16 deletions(-)
>>
>> diff --git a/drivers/gpu/drm/drm_edid.c b/drivers/gpu/drm/drm_edid.c
>> index 64f7a94dd9e4..a52fd6de9327 100644
>> --- a/drivers/gpu/drm/drm_edid.c
>> +++ b/drivers/gpu/drm/drm_edid.c
>> @@ -6544,7 +6544,7 @@ static void drm_parse_vesa_specific_block(struct drm_connector *connector,
>>  	if (oui(vesa->oui[0], vesa->oui[1], vesa->oui[2]) != VESA_IEEE_OUI)
>>  		return;
>>  
>> -	if (sizeof(*vesa) != sizeof(*block) + block->num_bytes) {
>> +	if (block->num_bytes < 5) {
>>  		drm_dbg_kms(connector->dev,
>>  			    "[CONNECTOR:%d:%s] Unexpected VESA vendor block size\n",
>>  			    connector->base.id, connector->name);
>> @@ -6567,24 +6567,20 @@ static void drm_parse_vesa_specific_block(struct drm_connector *connector,
>>  		break;
>>  	}
>>  
>> -	if (!info->mso_stream_count) {
>> -		info->mso_pixel_overlap = 0;

This is no longer cleared for !info->mso_stream_count.

Perhaps the code could be reorganized to handle it better.

>> -		return;
>> -	}
>> -
>> -	info->mso_pixel_overlap = FIELD_GET(DISPLAYID_VESA_MSO_OVERLAP, vesa->mso);
>> -	if (info->mso_pixel_overlap > 8) {
>> +	if (info->mso_stream_count) {
>> +		info->mso_pixel_overlap = FIELD_GET(DISPLAYID_VESA_MSO_OVERLAP, vesa->mso);
>> +		if (info->mso_pixel_overlap > 8) {
>> +			drm_dbg_kms(connector->dev,
>> +				    "[CONNECTOR:%d:%s] Reserved MSO pixel overlap value %u\n",
>> +				    connector->base.id, connector->name,
>> +				    info->mso_pixel_overlap);
>> +			info->mso_pixel_overlap = 8;
>> +		}
>>  		drm_dbg_kms(connector->dev,
>> -			    "[CONNECTOR:%d:%s] Reserved MSO pixel overlap value %u\n",
>> +			    "[CONNECTOR:%d:%s] MSO stream count %u, pixel overlap %u\n",
>>  			    connector->base.id, connector->name,
>> -			    info->mso_pixel_overlap);
>> -		info->mso_pixel_overlap = 8;
>> +			    info->mso_stream_count, info->mso_pixel_overlap);
>>  	}
>> -
>> -	drm_dbg_kms(connector->dev,
>> -		    "[CONNECTOR:%d:%s] MSO stream count %u, pixel overlap %u\n",
>> -		    connector->base.id, connector->name,
>> -		    info->mso_stream_count, info->mso_pixel_overlap);
>>  }
>>  
>>  static void drm_update_vesa_specific_block(struct drm_connector *connector,

-- 
Jani Nikula, Intel