[Intel-gfx] Commit 0e32b39c ("drm/i915: add DP 1.2 MST support (v0.7)") breaking DP audio on T440s

[Paul Moore]

On Monday, May 11, 2015 04:06:37 AM David Airlie wrote:
> ----- Original Message -----
> > From: "Jani Nikula" <jani.nikula at linux.intel.com>
> > To: "Paul Moore" <paul at paul-moore.com>, "Dave Airlie"
> > <airlied at redhat.com>, intel-gfx at lists.freedesktop.org Cc: "Daniel
> > Gultsch" <daniel at gultsch.de>, linux-kernel at vger.kernel.org Sent: Monday,
> > 11 May, 2015 6:01:49 PM
> > Subject: Re: [Intel-gfx] Commit 0e32b39c ("drm/i915: add DP 1.2 MST
> > support (v0.7)") breaking DP audio on T440s> 
> > On Mon, 11 May 2015, Jani Nikula <jani.nikula at linux.intel.com> wrote:
> > > On Fri, 08 May 2015, Paul Moore <paul at paul-moore.com> wrote:
> > >> On Fri, Mar 13, 2015 at 11:19 PM, Paul Moore wrote:
> > >>> Ever since v3.17 I've had a problem with displayport audio on my
> > >>> system, but until lately I haven't had a chance to bisect the problem.
> > >>> After a few rounds I've isolated the buggy commit to 0e32b39c
> > >>> ("drm/i915: add DP 1.2 MST support (v0.7)").
> > >>> 
> > >>> Simply put, prior to v3.17 everything worked correctly: audio from my
> > >>> system was routed to my monitor via the DP connection and finally out
> > >>> to the speakers connected to the monitor.  However, starting with
> > >>> kernel v3.17 this no longer works.  The various PulseAudio tools all
> > >>> indicate that the HDMI/DP audio output is unplugged/not-available.
> > >>> I've tried a few different xrandr commands found via google and
> > >>> manpages but nothing short of reverting to v3.16 solves the problem.
> > >>> I'm hoping that someone with more understanding of the Intel graphics
> > >>> drivers will be able to make some sense of it all and provide a fix.
> > >>> I'm more than happy to provide additional information and test any
> > >>> patches you may have.
> > >>> 
> > >>> For reference, my system is a ThinkPad T440s with a "Intel Corporation
> > >>> Haswell-ULT Integrated Graphics Controller (rev 0b)" (according to
> > >>> lspci) connected to a Dell U3011 via a Gefen DP KVM.
> > >> 
> > >> Help?
> > >> 
> > >> The problem still exists on v4.0.1 and I know of at least one other
> > >> person that has reported the same problem.  As I said above, I'm
> > >> willing to do any additional debugging/testing needed, I just could
> > >> use some help on resolving this as I am definitely not a
> > >> X/graphics-driver expert.
> > > 
> > > Hmm, I never received your first mail.
> > > 
> > > Apparently audio on DP MST is problematic, and the debugging may get a
> > > bit involved. Please file a bug at [1] so we don't clutter the lists
> > > with logs etc. Please enable drm.debug=14 module parameter and attach
> > > (to the bug) dmesg all the way from boot to trying audio on the monitor.
> > >
>
> I started looking at this today, the audio driver needs serious work to
> make this happen, I'm trying to investigate how much work that is.

Hi Dave, Jani,

Thanks for take a look at this, I appreciate it.  It looks like the 
FreeDesktop BZ #89895 is the same problem I'm having so I added my information 
to that BZ.  Let me know if there is anything else I can do to help.

 * https://bugs.freedesktop.org/show_bug.cgi?id=89895

-Paul

-- 
paul moore
www.paul-moore.com