linux-kernel - Re: [REGRESSION] i915: failure to see Dell 30" monitor connected to a Lenovo Haswell docking station

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Date:	Tue, 2 Sep 2014 21:23:16 +1000
From:	Dave Airlie <airlied@...il.com>
To:	"Theodore Ts'o" <tytso@....edu>, Dave Airlie <airlied@...il.com>,
	Daniel Vetter <daniel.vetter@...ll.ch>,
	dri-devel <dri-devel@...ts.freedesktop.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Jani Nikula <jani.nikula@...el.com>
Subject: Re: [REGRESSION] i915: failure to see Dell 30" monitor connected to a
 Lenovo Haswell docking station

On 2 September 2014 21:03, Theodore Ts'o <tytso@....edu> wrote:
> On Tue, Sep 02, 2014 at 02:15:39PM +1000, Dave Airlie wrote:
>> On 2 September 2014 14:05, Theodore Ts'o <tytso@....edu> wrote:
>> > I recently upgraded to v3.17-rc3, and on my Lenovo T540p, I can no
>> > longer see the my Dell 30" monitor when it is connected via the
>> > docking station using a Displayport connector.  This worked using 3.16
>> > kernel.
>> >
>> > If I connect to the monitor using the mini-display, by passing the
>> > docking station, things work fine (but of course it's annoying not to
>> > be able to use the docking station).
>> >
>> > Is this a known problem?  This is not the first time that we've had
>> > regressions with this docking station.   It's vaguely reminsicent of
>> >
>> >         https://bugs.freedesktop.org/show_bug.cgi?id=71267
>> >
>> > Except the system isn't hanging; it's just not seeing the monitor at all.
>>
>> Have you the Dell 30" set to Displayport 1.2 enabled mode?
>
> No, it DP 1.2 was disabled.  If I enable it, it breaks things when I
> try connecting via the MiniDP port (bypassing the dock), and it is
> still broken when I try to talk via the DisplayPort in the dock.
>
> If I disable DP 1.2 again, it works via the MiniDP port, but if I try
> to connect through the dock (which has a DP Hub which I believe is
> MST/DP 1.2 capable), it is still broken.
>
> It does seem that this might be related to 3.17-rc3 trying to talk DP
> 1.2 if it is available, since I can't control what the DP hub in the
> docking station advertises --- is there a commit or some kind of hack
> I can try to force talking to the DP hub using DP 1.1?
>

Interesting, I have the same combo of hw available on my desk at work,
but it might be a couple of days before I can get to the office to
debug it,

can you boot with drm.debug=6 and get me the dmesg?

The attached hack turns off mst so might be useful as a workaround,
but I should be able to fix this once I sit down at my desk.

Dave.

View attachment "i915-mst-hack.patch" of type "text/x-patch" (332 bytes)