Second Monitor Issue on Kernel 6.1.5

Second Monitor Issue on Kernel 6.1.5

[Matthew Fahner]

Hello,

I'm running Ubuntu 20.10 and experienced a regression when trying
kernel 6.1.5 that was not present in previous kernels such as 6.0.19
or 6.0.9

I have two monitors attached using DisplayPort MST (daisy chaining the
displays).

Normally, this works without issue and both monitors are detected and
display properly.

With kernel 6.1.5, the second monitor (the monitor that's not directly
connected to the computer) was detected but would not display.  I
didn't spend much time troubleshooting the issue and instead reverted
to 6.0.19 where it again worked without issue.  The first monitor
worked without issue.

Let me know what steps I can take to help identify the root cause.

  -Matt

Re: Second Monitor Issue on Kernel 6.1.5

[Greg KH]

On Fri, Jan 13, 2023 at 11:58:47PM -0500, Matthew Fahner wrote:
> Hello,
> 
> I'm running Ubuntu 20.10 and experienced a regression when trying
> kernel 6.1.5 that was not present in previous kernels such as 6.0.19
> or 6.0.9
> 
> I have two monitors attached using DisplayPort MST (daisy chaining the
> displays).
> 
> Normally, this works without issue and both monitors are detected and
> display properly.
> 
> With kernel 6.1.5, the second monitor (the monitor that's not directly
> connected to the computer) was detected but would not display.  I
> didn't spend much time troubleshooting the issue and instead reverted
> to 6.0.19 where it again worked without issue.  The first monitor
> worked without issue.
> 
> Let me know what steps I can take to help identify the root cause.

Can you use 'git bisect' to track down the offending commit?

thanks,

greg k-h

Re: Second Monitor Issue on Kernel 6.1.5

[Salvatore Bonaccorso]

Hi,

On Sat, Jan 14, 2023 at 07:56:50AM +0100, Greg KH wrote:
> On Fri, Jan 13, 2023 at 11:58:47PM -0500, Matthew Fahner wrote:
> > Hello,
> > 
> > I'm running Ubuntu 20.10 and experienced a regression when trying
> > kernel 6.1.5 that was not present in previous kernels such as 6.0.19
> > or 6.0.9
> > 
> > I have two monitors attached using DisplayPort MST (daisy chaining the
> > displays).
> > 
> > Normally, this works without issue and both monitors are detected and
> > display properly.
> > 
> > With kernel 6.1.5, the second monitor (the monitor that's not directly
> > connected to the computer) was detected but would not display.  I
> > didn't spend much time troubleshooting the issue and instead reverted
> > to 6.0.19 where it again worked without issue.  The first monitor
> > worked without issue.
> > 
> > Let me know what steps I can take to help identify the root cause.
> 
> Can you use 'git bisect' to track down the offending commit?

Not the reporter, but I suspect this is
https://gitlab.freedesktop.org/drm/amd/-/issues/2171 .

Matthew can you verify this matches? There is as well context on this
issue on this thread:

https://lore.kernel.org/stable/8502e5d8-8444-e256-54f3-0c488b54686a@amd.com/

FWIW, we had a similar bugreport downstream in Debian:
https://bugs.debian.org/1028451

Regards,
Salvatore

Re: Second Monitor Issue on Kernel 6.1.5

[Matthew Fahner]

Hi Salvatore,

Thanks, yes, that does appear to match my issue.

The Debian bug report seems to have identified as commit
4d07b0bc403403438d9cf88450506240c5faf92f

I'll keep an eye on those threads and test again once it's believed to
be updated.

-Matt

On Sat, 14 Jan 2023 at 09:52, Salvatore Bonaccorso <carnil@debian.org> wrote:
>
> Hi,
>
> On Sat, Jan 14, 2023 at 07:56:50AM +0100, Greg KH wrote:
> > On Fri, Jan 13, 2023 at 11:58:47PM -0500, Matthew Fahner wrote:
> > > Hello,
> > >
> > > I'm running Ubuntu 20.10 and experienced a regression when trying
> > > kernel 6.1.5 that was not present in previous kernels such as 6.0.19
> > > or 6.0.9
> > >
> > > I have two monitors attached using DisplayPort MST (daisy chaining the
> > > displays).
> > >
> > > Normally, this works without issue and both monitors are detected and
> > > display properly.
> > >
> > > With kernel 6.1.5, the second monitor (the monitor that's not directly
> > > connected to the computer) was detected but would not display.  I
> > > didn't spend much time troubleshooting the issue and instead reverted
> > > to 6.0.19 where it again worked without issue.  The first monitor
> > > worked without issue.
> > >
> > > Let me know what steps I can take to help identify the root cause.
> >
> > Can you use 'git bisect' to track down the offending commit?
>
> Not the reporter, but I suspect this is
> https://gitlab.freedesktop.org/drm/amd/-/issues/2171 .
>
> Matthew can you verify this matches? There is as well context on this
> issue on this thread:
>
> https://lore.kernel.org/stable/8502e5d8-8444-e256-54f3-0c488b54686a@amd.com/
>
> FWIW, we had a similar bugreport downstream in Debian:
> https://bugs.debian.org/1028451
>
> Regards,
> Salvatore