Re: v3.5 Oops in i2c_algo_bit.c:bit_xfer+0x23/0x870: i915 or i2c?

["George Spelvin" <linux@horizon.com>]

(Bringing this back to the mailing lists after a bit of uninteresting private
conversation.)

> Honestly, I think we need a way to force disable gmbus with a module 
> parameter or something anyway. It's not the first time gmbus has been 
> implicated with an issue. Maybe it even exists already, but I couldn't 
> find this. So if you confirm that fixes the problem for you on the ml, 
> at least maybe such a patch will be the result.
>
> If you feel it's a software bug (which I agree it seems likely), a
> bisect is always much appreciated. Personally, I'll usually step back
> major releases until something works, or I hit 3.2ish. Even knowing it
> never worked through 3.2 is helpful.

It's a friend's machine, which I normally only have remote access to,
so it's a bit pf a pain, but I can manage.  I just thought a basic
i3 motherboard was so common I couldn't possibly be the only one with
this problem.

Here's the 3.2 dmesg showing the fallback working, but this is an
Ubuntu-patched kernel (linux-image-3.2.0-29-generic) that may be a fair
distance from stock:

[   44.401124] [drm] Initialized drm 1.1.0 20060810
[   44.471549] i915 0000:00:02.0: PCI INT A -> GSI 16 (level, low) -> IRQ 16
[   44.471553] i915 0000:00:02.0: setting latency timer to 64
[   44.555865] [drm] GMBUS timed out, falling back to bit banging on pin 0 [i915 gmbus disabled]
[   44.611882] [drm] GMBUS timed out, falling back to bit banging on pin 0 [i915 gmbus disabled]
[   44.667876] [drm] GMBUS timed out, falling back to bit banging on pin 0 [i915 gmbus disabled]
[   44.723831] [drm] GMBUS timed out, falling back to bit banging on pin 0 [i915 gmbus disabled]
[   44.779841] [drm] GMBUS timed out, falling back to bit banging on pin 0 [i915 gmbus disabled]
[   44.835854] [drm] GMBUS timed out, falling back to bit banging on pin 0 [i915 gmbus disabled]
[   44.895843] [drm] GMBUS timed out, falling back to bit banging on pin 0 [i915 gmbus disabled]
[   44.951836] [drm] GMBUS timed out, falling back to bit banging on pin 0 [i915 gmbus disabled]
[   45.007798] [drm] GMBUS timed out, falling back to bit banging on pin 0 [i915 gmbus ssc]
[   45.063716] [drm] GMBUS timed out, falling back to bit banging on pin 0 [i915 gmbus ssc]
[   45.119776] [drm] GMBUS timed out, falling back to bit banging on pin 0 [i915 gmbus ssc]
[   45.175716] [drm] GMBUS timed out, falling back to bit banging on pin 0 [i915 gmbus ssc]
[   45.231689] [drm] GMBUS timed out, falling back to bit banging on pin 0 [i915 gmbus ssc]
[   45.287696] [drm] GMBUS timed out, falling back to bit banging on pin 0 [i915 gmbus ssc]
[   45.343704] [drm] GMBUS timed out, falling back to bit banging on pin 0 [i915 gmbus ssc]
[   45.399667] [drm] GMBUS timed out, falling back to bit banging on pin 0 [i915 gmbus ssc]
[   45.455651] [drm] GMBUS timed out, falling back to bit banging on pin 0 [i915 gmbus vga]
[   45.511629] [drm] GMBUS timed out, falling back to bit banging on pin 0 [i915 gmbus vga]
[   45.567581] [drm] GMBUS timed out, falling back to bit banging on pin 0 [i915 gmbus vga]
[   45.623645] [drm] GMBUS timed out, falling back to bit banging on pin 0 [i915 gmbus vga]
[   45.679546] [drm] GMBUS timed out, falling back to bit banging on pin 0 [i915 gmbus vga]
[   45.735614] [drm] GMBUS timed out, falling back to bit banging on pin 0 [i915 gmbus vga]
[   45.791596] [drm] GMBUS timed out, falling back to bit banging on pin 0 [i915 gmbus vga]
[   45.847533] [drm] GMBUS timed out, falling back to bit banging on pin 0 [i915 gmbus vga]
[   45.903517] [drm] GMBUS timed out, falling back to bit banging on pin 0 [i915 gmbus panel]
[   45.959547] [drm] GMBUS timed out, falling back to bit banging on pin 0 [i915 gmbus panel]
[   46.015492] [drm] GMBUS timed out, falling back to bit banging on pin 0 [i915 gmbus panel]
[   46.071473] [drm] GMBUS timed out, falling back to bit banging on pin 0 [i915 gmbus panel]
[   46.127430] [drm] GMBUS timed out, falling back to bit banging on pin 0 [i915 gmbus panel]
[   46.183447] [drm] GMBUS timed out, falling back to bit banging on pin 0 [i915 gmbus panel]
[   46.239425] [drm] GMBUS timed out, falling back to bit banging on pin 0 [i915 gmbus panel]
[   46.295407] [drm] GMBUS timed out, falling back to bit banging on pin 0 [i915 gmbus panel]
[   46.351401] [drm] GMBUS timed out, falling back to bit banging on pin 0 [i915 gmbus dpc]
[   46.407382] [drm] GMBUS timed out, falling back to bit banging on pin 0 [i915 gmbus dpc]
[   46.463363] [drm] GMBUS timed out, falling back to bit banging on pin 0 [i915 gmbus dpc]
[   46.519347] [drm] GMBUS timed out, falling back to bit banging on pin 0 [i915 gmbus dpc]
[   46.575302] [drm] GMBUS timed out, falling back to bit banging on pin 0 [i915 gmbus dpc]
[   46.631320] [drm] GMBUS timed out, falling back to bit banging on pin 0 [i915 gmbus dpc]
[   46.687360] [drm] GMBUS timed out, falling back to bit banging on pin 0 [i915 gmbus dpc]
[   46.743300] [drm] GMBUS timed out, falling back to bit banging on pin 0 [i915 gmbus dpc]
[   46.799250] [drm] GMBUS timed out, falling back to bit banging on pin 0 [i915 gmbus dpb]
[   46.855292] [drm] GMBUS timed out, falling back to bit banging on pin 0 [i915 gmbus dpb]
[   46.911250] [drm] GMBUS timed out, falling back to bit banging on pin 0 [i915 gmbus dpb]
[   46.967250] [drm] GMBUS timed out, falling back to bit banging on pin 0 [i915 gmbus dpb]
[   47.023258] [drm] GMBUS timed out, falling back to bit banging on pin 0 [i915 gmbus dpb]
[   47.079206] [drm] GMBUS timed out, falling back to bit banging on pin 0 [i915 gmbus dpb]
[   47.135232] [drm] GMBUS timed out, falling back to bit banging on pin 0 [i915 gmbus dpb]
[   47.191163] [drm] GMBUS timed out, falling back to bit banging on pin 0 [i915 gmbus dpb]
[   47.247148] [drm] GMBUS timed out, falling back to bit banging on pin 0 [i915 gmbus reserved]
[   47.303186] [drm] GMBUS timed out, falling back to bit banging on pin 0 [i915 gmbus reserved]
[   47.359091] [drm] GMBUS timed out, falling back to bit banging on pin 0 [i915 gmbus reserved]
[   47.415157] [drm] GMBUS timed out, falling back to bit banging on pin 0 [i915 gmbus reserved]
[   47.471062] [drm] GMBUS timed out, falling back to bit banging on pin 0 [i915 gmbus reserved]
[   47.527121] [drm] GMBUS timed out, falling back to bit banging on pin 0 [i915 gmbus reserved]
[   47.583087] [drm] GMBUS timed out, falling back to bit banging on pin 0 [i915 gmbus reserved]
[   47.639092] [drm] GMBUS timed out, falling back to bit banging on pin 0 [i915 gmbus reserved]
[   47.695081] [drm] GMBUS timed out, falling back to bit banging on pin 0 [i915 gmbus dpd]
[   47.751011] [drm] GMBUS timed out, falling back to bit banging on pin 0 [i915 gmbus dpd]
[   47.810995] [drm] GMBUS timed out, falling back to bit banging on pin 0 [i915 gmbus dpd]
[   47.867014] [drm] GMBUS timed out, falling back to bit banging on pin 0 [i915 gmbus dpd]
[   47.923009] [drm] GMBUS timed out, falling back to bit banging on pin 0 [i915 gmbus dpd]
[   47.978921] [drm] GMBUS timed out, falling back to bit banging on pin 0 [i915 gmbus dpd]
[   48.034954] [drm] GMBUS timed out, falling back to bit banging on pin 0 [i915 gmbus dpd]
[   48.090936] [drm] GMBUS timed out, falling back to bit banging on pin 0 [i915 gmbus dpd]
[   48.091142] i915 0000:00:02.0: irq 49 for MSI/MSI-X
[   48.091147] [drm] Supports vblank timestamp caching Rev 1 (10.10.2010).
[   48.091148] [drm] Driver supports precise vblank timestamp query.
[   48.091182] vgaarb: device changed decodes: PCI:0000:00:02.0,olddecodes=io+mem,decodes=io+mem:owns=io+mem
[   48.511902] fbcon: inteldrmfb (fb0) is primary device
[   48.852752] Console: switching to colour frame buffer device 240x67
[   48.857087] fb0: inteldrmfb frame buffer device
[   48.857088] drm: registered panic notifier
[   48.857205] [drm] Initialized i915 1.6.0 20080730 for 0000:00:02.0 on minor 0