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

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Message-ID: <ebd974b5-88f4-4fb3-a135-bad3bf7d9b4d@0la.ch>
Date: Wed, 26 Nov 2025 15:50:18 +0100
From: Yaroslav <iam@....ch>
To: Jani Nikula <jani.nikula@...ux.intel.com>, 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
Subject: Re: [PATCH v6 2/7] drm/edid: prepare for VESA vendor-specific data
 block extension



On 2025-11-26 15:08, Jani Nikula wrote:
> 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.

It defaults to zero due to drm_reset_display_info()

>>> -		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,
>