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SubjectRe: [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 <> wrote:
> On Fri, 08 May 2015, Paul Moore <> 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.
> BR,
> Jani.


>> -Paul
>> --
>> paul moore
>> _______________________________________________
>> Intel-gfx mailing list
> --
> Jani Nikula, Intel Open Source Technology Center

Jani Nikula, Intel Open Source Technology Center

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