[REGRESSION] Re: i915 driver crashes on T540p if docking station attached

[Richard Harman]

(long time lurker, first time poster)

This (because the dock has a DP MST hub built in) reminds me of this
crash w/ my W540 - which I think are pretty similar hardware:

https://bugzilla.redhat.com/show_bug.cgi?id=1180747

Not enough of a coder to really troubleshoot, but I've got a dock, a MST
hub, and I'm willing to compile & test patches.  I've mostly left the HW
... disused because I was disgusted that my W530 could drive four
displays at once, and the W540 appears incapable due to the Intel chip
only supporting 3 CRTCs.

How can I help?

On 07/29/15 21:39, Theodore Ts'o wrote:
> On Wed, Jul 29, 2015 at 08:49:37PM -0400, Theodore Ts'o wrote:
>> Unfortunately the failure causes a series of recursive faults and I
>> haven't been able to capture the stack trace, but on 4.2-rcX kernels,
>> I can reliably cause the system to crash if my T540p is booted with
>> the docking station attached.
>>
>> It will also crash if I boot the system first, and then insert the
>> laptop into the dockstation.
>>
>> Unfortunately, I can't get a stack trace because there are a huge
>> number of recursive/double faults, and the system dies so quickly that
>> nothing ends up in the log files.  If you really need a stack dump I
>> can try to rig something, but modern Laptops don't have serial
>> consoles any more, alas, so it's bit of a pain.
> The bad news is that I tried to use kdump to capture a crashdump and
> hopefully get more information, and kdump utterly wedged on the panic.
> The good news is because it wedged the system, I was able to get the
> console stackdump before it scrolled off due to a whole series of
> recursive oops messages.
>
> It's here:  https://goo.gl/photos/xHjn2Z97JQEw6k2C9
>
> Hopefully tihs is useful.  It's not obvious how to revert this change,
> since there were a large number of changes to i915 after this.  If
> someone could help me with a revert, I'd be happy to test it.
>
> Thanks,
>
> 						- Ted
> 						
>
>
>> I was able to bisect it down to this commit, however: 8c7b5ccb72987:
>> "drm/i915: Use atomic helpers for computing changed flags:"
>>
>> Is there any chance Intel could add a Lenovo Dockstation with a
>> Multistream DP output to part of your test hardware?  Unfortunately it
>> seems pretty common that I see regressions with my particular
>> hardware.  Maybe there aren't enough people using Thinkpads any more?  :-(
>>
>>       	     	    	   	 	       	      - Ted
>>
>>
>> P.S.  The git bisect log
>>
>> git bisect start
>> # bad: [421d125c06c4be4c5005cb69840206bd09b71dd6] builddeb: sign the modules after splitting out the debuginfo files
>> git bisect bad 421d125c06c4be4c5005cb69840206bd09b71dd6
>> # good: [b953c0d234bc72e8489d3bf51a276c5c4ec85345] Linux 4.1
>> git bisect good b953c0d234bc72e8489d3bf51a276c5c4ec85345
>> # good: [aeaa2122af4e53f3bfd28e8f294557bb95af43fc] drm/i915/skl: Add the INIT power domain to the MISC I/O power well
>> git bisect good aeaa2122af4e53f3bfd28e8f294557bb95af43fc
>> # bad: [4d70f38a760ad2879d2ebd84001c92980180f630] drm/i915/bios: remove a redundant NULL pointer check
>> git bisect bad 4d70f38a760ad2879d2ebd84001c92980180f630
>> # bad: [27a1b688d9f1fa2abd14bfe6a8729a19fb3b1b25] drm/i915/bxt: Enable WaEnableYV12BugFixInHalfSliceChicken7 for Broxton
>> git bisect bad 27a1b688d9f1fa2abd14bfe6a8729a19fb3b1b25
>> # good: [4be0731786de10d0e9ae1d159504c83c6b052647] drm/i915: Add crtc states before calling compute_config()
>> git bisect good 4be0731786de10d0e9ae1d159504c83c6b052647
>> # good: [d5432a9d19b61ba6a2b3d88f3026e0ca60eb57a1] drm/i915: Stage new modeset state straight into atomic state
>> git bisect good d5432a9d19b61ba6a2b3d88f3026e0ca60eb57a1
>> # bad: [a821fc46bc7bb6d4cf9a5f8d2787fd70231c2c10] drm/i915: Swap atomic state in legacy modeset
>> git bisect bad a821fc46bc7bb6d4cf9a5f8d2787fd70231c2c10
>> # bad: [8c7b5ccb729870e606321b3703e2c2e698c49a95] drm/i915: Use atomic helpers for computing changed flags
>> git bisect bad 8c7b5ccb729870e606321b3703e2c2e698c49a95
>> # good: [0f63cca2afdc38877e86acfa9821020f6e2213fd] drm/i915: Update crtc state active flag based on DPMS
>> git bisect good 0f63cca2afdc38877e86acfa9821020f6e2213fd
>> # good: [840bfe953384a134c8639f2964d9b74bfa671e16] drm/atomic: Make mode_fixup() optional for check_modeset()
>> git bisect good 840bfe953384a134c8639f2964d9b74bfa671e16
>> # first bad commit: [8c7b5ccb729870e606321b3703e2c2e698c49a95] drm/i915: Use atomic helpers for computing changed flags
>>
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