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

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Message-ID: <61a482c23a81dc29f1fb793064c7238a98cf0143@intel.com>
Date: Wed, 26 Nov 2025 16:59:09 +0200
From: Jani Nikula <jani.nikula@...ux.intel.com>
To: Yaroslav <iam@....ch>, 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 Wed, 26 Nov 2025, Yaroslav <iam@....ch> wrote:
> 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()

Yes, and the code above the context initializes it from the vendor
block.


>
>>>> -		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