Re: [3.0.0-rc3] GMBUS timed out

From: Chris Wilson
Date: Thu Jun 16 2011 - 10:08:57 EST

On Thu, 16 Jun 2011 15:41:23 +0200, Paul Rolland (=?UTF-8?B?44Od44O844Or44O744Ot44Op44Oz?=) <rol@xxxxxxxxx> wrote:
> Hello,
> I've just booted 3.0.0-rc3 on my machine, and I got that message :
> Jun 16 15:32:07 tux kernel: [drm] GMBUS timed out, falling back to bit banging on pin 5 [i915 gmbus dpb]
> I've checked my logs, and I never got that with my previous
> kernel, so that looks like something new to 3.x.

Attempting to use GMBUS when enabled for 3.0. It will have to be
disabled again until the GMBUS/GPIO adapter aligns better with the i2c
interface and doesn't cause a deadlock upon booting with the eeprom

In the meantime, if you have the time and inclination, you can help by
working out under what conditions GMBUS fails. That info message is only
generated after we write a message over GMBUS and receive no response.
I've looked into one exchange that suggests that we may timeout if the
monitor is disconnected. Do you have anything connected to what would be
the first external output? Does the message go away if you boot with
that connected/disconnected?

> Should I report more details (and if so, which ones) or is that harmless
> (though I doubt kernel messages about a time out are harmless ;)

It's harmless in this case. Just a warning that the new hw driven method
failed and we are now using the old CPU driven method.

Chris Wilson, Intel Open Source Technology Centre
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