RE: [External Mail] Re: Test result / finding of "drm/amd/display: Consult MCCS FreeSync cap only if requested & supported"

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> -----Original Message-----
> From: Thorsten Leemhuis <[email protected]>
> Sent: Thursday, May 28, 2026 7:17 AM
> To: Michel Dänzer <[email protected]>; Pei-Hsin Yang
> <[email protected]>
> Cc: [email protected]; Linux kernel regressions list
> <[email protected]>; Deucher, Alexander
> <[email protected]>; Koenig, Christian
> <[email protected]>
> Subject: Re: [External Mail] Re: Test result / finding of "drm/amd/display:
> Consult MCCS FreeSync cap only if requested & supported"
>
> [+Alex +Christian]
>
> On 5/21/26 09:09, Michel Dänzer wrote:
> > On 5/20/26 17:54, Pei-Hsin Yang wrote:
> >>
> >>> Tested with 3 HDMI sinks with different FreeSync/HDMI VRR capabilities.  I
> saw one case that a FreeSync sink (Dell S2721HS) with E6h VCP code
> supported was detected as FreeSync capable at beginning but identified as not
> FreeSync capable later – after do_mccs is changed from true to false.
> >>
> >>>> And that doesn't happen without my patch applied?
> >>
> >> There are other issues without your patch applied.   One issue is that if a
> FreeSync capable sink with MCCS VCP Code = 0 (mostly are TVs), it will be
> detected as not FreeSync supported and VRR will be disabled.
> >
> > That sounds similar to https://gitlab.freedesktop.org/drm/amd/-
> /work_items/5286 .
> >
> > I was wondering if the specific issue you described above with Dell S2721HS
> is reproducible without my patch though, in which case it might be a separate
> regression (and wouldn't speak against merging my patch).
> >
> >
> >>>> TBH I don't really want to be fixing the regression I hit, I'd prefer the AMD
> display team to handle it.
> >>
> >> Yes, agreed.  As FreeSync MCCS support has immediate impacts to Valve's
> Steam devices, I will work with AMD display team to handle it.   HDMI 2.1 VRR
> and VTEM packet sending support need to be included as well.
> >
> > Note that some kind of short-term solution is needed for the regression(s) in
> 7.1-rc.
>
> Yeah, that would be good. Makes me wonder how the rough plan to realize
> this looks like? Sounds like Michael's patch[1] that was discussed here is not a
> good option? Reminder, Linus ideally wants known regression fixed by -rc6,
> which is why I'm asking.

@Wentland, Harry can you sort this out for next week's -fixes PR?

Alex

>
> Ciao, Thorsten
>
> [1]
> https://lore.kernel.org/amd-gfx/20260518154809.660061-1-
> [email protected]/