Re: [RFC] i2c: Providing hooks for i2c multimaster bus arbitration.

[Simon Glass <sjg@google.com>]

On Mon, Feb 11, 2013 at 3:53 PM, Doug Anderson <dianders@chromium.org> wrote:
> Wolfram,
>
> On Sun, Feb 10, 2013 at 10:17 AM, Wolfram Sang <w.sang@pengutronix.de> wrote:
>> On Mon, Feb 04, 2013 at 02:33:15PM +0530, Yuvaraj Kumar C D wrote:
>>> This RFC patch is w.r.t multimaster bus arbitration which is already
>>> being discussing in the mainline.
>>> This patch provides hooks for the i2c multimaster bus arbitration
>>> and to have the arbitration parameters.
>>
>> I still haven't understood why the arbitration specified in the I2C
>> standard is not enough for you. Or what you would need to make use of
>> it.
>
> At the moment perhaps the strongest argument for why this particular
> arbitration scheme is needed is that's what the EC (embedded
> controller) on the ARM Chromebook uses.  There have been several
> arguments in-house about whether this was the most ideal way to
> structure things, but that's what we shipped with.  Thus, if we want
> to be able to talk to i2c devices on this bus (contains the keyboard,
> battery, and a bunch of power switches) we need something in the
> system that implements this arbitration scheme.
>

There was some discussion about using the built-in I2C multi-master
support but no one had had a good experience getting it to work
reliably in a real system so we ended up deciding not to rely on this.

> As a side note: I'm trying to code up a quick arbitrator now using the
> muxing framework as Grant suggested.  I will play with this and post
> it if I can get it to work.  It's quite short so far.
>
> -Doug