[Nouveau] External monitor remains black - nouveau reports "link training failed"

[Ilia Mirkin]

On Wed, Sep 16, 2015 at 1:14 PM, Fredy Neeser <nfd at zurich.ibm.com> wrote:
>
> Hello list,
>
> I had a working dual-monitor setup with KDE Plasma 5 on a Lenovo W530
> "Optimus" laptop (hybrid graphics, nouveau + i915 drivers), but it seems to
> fall apart with recent kernels, i.e., the external monitor (connected to
> the laptop's docking station via DisplayPort) no longer works.
>
> My setup still works fine with kernels up to and including
> 4.1.3-201.fc22.x86_64, but  with kernel  4.1.6-200.fc22  (as well as
> another update on top of 4.1.6), the external monitor remains black, and
> the journal shows several lines
>
>     kernel: nouveau E[   PDISP][0000:01:00.0][0x00000006] 06:0006:0f48:
> link training failed
>
> not present with previous kernels -- see also
>
>   https://bugzilla.redhat.com/show_bug.cgi?id=1260053
>   Bug 1260053 - External monitor remains black with kernel
> 4.1.6-200.fc22.x86_64 - nouveau reports "link training failed"
>
>
> Could this be related to some changes in powering down the DPs (which
> requires link training to resume)?
>
> Any ideas for debugging / narrowing down the issue are much appreciated !

Looking at the nouveau changes between v4.1.3 and v4.1.6 -- nothing
looks particularly relevant. You could try reverting stable tree
commit 140d4baa12 (commit 697bb728d9 upstream) but if that's the
cause, then.... I'll be quite surprised.

Can you see if perhaps Redhat added some additional custom patches in
the 4.1.6 builds? Not sure where they list that stuff, and am not
particularly inclined to search myself.

If manually looking at these things doesn't reveal anything, doing a
bisect is going to be your best bet.

Cheers,

  -ilia