linux-kernel - Re: [PATCH v3] Bitbanging i2c bus driver using the GPIO API

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Date:	Mon, 23 Apr 2007 11:42:54 +0200
From:	Jean Delvare <khali@...ux-fr.org>
To:	Lennart Sorensen <lsorense@...lub.uwaterloo.ca>
Cc:	Haavard Skinnemoen <hskinnemoen@...el.com>,
	David Brownell <david-b@...bell.net>,
	Bryan Wu <bryan.wu@...log.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Deepak Saxena <dsaxena@...xity.net>,
	linux-kernel@...r.kernel.org,
	Christer Weinigel <wingel@...o-system.com>,
	Jordan Crouse <jordan.crouse@....com>
Subject: Re: [PATCH v3] Bitbanging i2c bus driver using the GPIO API

Lennart,

On Sun, 22 Apr 2007 11:41:51 -0400, Lennart Sorensen wrote:
> On Fri, Apr 20, 2007 at 07:49:33PM +0200, Jean Delvare wrote:
> > The scx200_acb driver was heavily modified in 2.6.17 and 2.6.18, not
> > much since then. I am not familiar with the hardware so I can't comment
> > on which chips are supposed to work and which aren't.
> 
> Well 2.6.18's scx200_acb works on the geode LX module I have, but no on
> the geode sc1200 module (where scx200_i2c does work).
> 
> scx200_acb doesn't detect any device that it can drive (nothing in dmesg
> at all when loaded) on the sc1200.

On the SCx200, the scx200_acb driver doesn't actually detect the
device. It uses arbitrary I/O addresses and hopes for the best. By
default, two buses are created, at 0x820 and 0x840. This might simply
not be the right addresses for your board. See
Documentation/i2c/busses/scx200_acb.

You should enable CONFIG_I2C_DEBUG_BUS and see what the driver says
when being loaded.

I seem to remember there has been a patch floating around to
auto-detect the right ports back in June 2006, but it seems to have
been lost somehow. Jordan, do you remember?

> I believe the main changes that
> happened to scx200_acb was adding support for the newer CSxxxx chipsets,
> such as the one used with the geode LX (which does work now).

Not only. There was also a log of bug fixing.

-- 
Jean Delvare
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