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Message-ID: <8a940fa4-ac9a-44b6-9d4a-e5394b0d6bf7@0la.ch>
Date: Wed, 26 Nov 2025 16:26:29 +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 16:06, Yaroslav wrote:
>
>
> On 2025-11-26 15:59, Jani Nikula wrote:
>> 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.
>>
>
> It is wrapped in `if (info->mso_stream_count)` so we get
>
> /* From drm_reset_display_info */
> info->mso_pixel_overlap = 0;
>
> /* This part was removed, as we don't want the early return here anymore
> due to extended structure length checks
> if (!info->mso_stream_count) {
> info->mso_pixel_overlap = 0;
> return;
> } */
>
>
> /* This code is right below your comment */
> if (info->mso_stream_count) {
> info->mso_pixel_overlap = ...;
> ...
> }
>
> /* I can reinsert the value reset explicitly here, if that's what you
> suggesting to do:
>
> else {
> info->mso_pixel_overlap = 0;
> }*/
>
>
For reference, repository state at the point after this patch:
https://github.com/CertainLach/linux-1/blob/01b0097171ebe85ae124a7b535dce0b46a1dd8e2/drivers/gpu/drm/drm_edid.c#L6561-L6593
Commit:
https://github.com/CertainLach/linux-1/commit/01b0097171ebe85ae124a7b535dce0b46a1dd8e2
(Note that the fix for DP/EDP mistake is already here, but nothing else
was changed in the github version of this patch)
>
>>
>>>
>>>>>> - 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,
>>>>
>>>
>>
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