linux-kernel - Re: [PATCH] drm/i915/sdvo: Reorder i2c initialisation before ddc proxy

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Message-ID: <yun8vu42hsl.fsf@aiko.keithp.com>
Date:	Wed, 18 May 2011 07:40:42 -0700
From:	Keith Packard <keithp@...thp.com>
To:	Chris Wilson <chris@...is-wilson.co.uk>,
	Mihai Moldovan <ionic@...ic.de>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] drm/i915/sdvo: Reorder i2c initialisation before ddc proxy

On Wed, 18 May 2011 09:04:11 +0100, Chris Wilson <chris@...is-wilson.co.uk> wrote:
> On Tue, 17 May 2011 18:22:52 -0700, Keith Packard <keithp@...thp.com> wrote:
> > On Tue, 17 May 2011 14:03:50 +0100, Chris Wilson <chris@...is-wilson.co.uk> wrote:
> > > The ddc proxy depends upon the underlying i2c bus being selected. Under
> > > certain configurations, the i2c-adapter functionality is queried during
> > > initialisation and so may trigger an OOPS during boot. Hence, we need to
> > > reorder the initialisation of the ddc proxy until after we hook up the i2c
> > > adapter for the SDVO device.
> > 
> > I'd love more explanation here about how this code ever worked -- what
> > are these 'certain configurations' of which you speak?
> 
> The condition under which it fails is when the i2c_add_adapter calls into
> i2c_detect which will attempt to probe all valid addresses on the adapter
> iff there is a pre-existing i2c_driver with the same class as the freshly
> added i2c_adapter.

Lovely.

> So it appears to depend upon having compiled in (or loaded such a module
> before i915.ko) an i2c-driver that likes to futz over the i2c_adapters
> claiming DDC support.

Thanks for your additional explanation, as I said, the patch looks sane
on the face of it (always nice to initialize values before use).

I've marked this as reviewed, added your additional explanation and
merged it to drm-intel-next. Seems like it might like a cc to stable?

-- 
keith.packard@...el.com

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