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

[Jani Nikula]

On Fri, 08 May 2015, Paul Moore <paul at paul-moore.com> wrote:
> On Fri, Mar 13, 2015 at 11:19 PM, Paul Moore <paul at paul-moore.com> 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.

BR,
Jani.


>
> -Paul
>
> -- 
> paul moore
> www.paul-moore.com
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-- 
Jani Nikula, Intel Open Source Technology Center