Subject: Re: New i2c framework
To: Eduardo Horvath <eeh@NetBSD.ORG>
From: Jason Thorpe <>
List: tech-kern
Date: 07/31/2003 09:01:08
On Thursday, July 31, 2003, at 08:43  AM, Eduardo Horvath wrote:

> But they are separate address spaces, so don't you need some way to
> differentiate between communications to a 7-bit device or a 10-bit
> device at the same address?

I need to reread the I2C spec before I can answer this question.

> Huh?  How does that prevent you from doing direct configuration?

Direct configuration requires being able to deterministically identify 
a device based on some unique cookie.  I2C does not have that.

Chris's suggestion of a hybrid approach using a platform-specific table 
could be useful, but pure direct configuration like is possible on e.g. 
SBus or PCI is simply not possible on I2C.

> So...  How does a userland program issue commands that require
> repeated starts?

With regard to more complex operations being directed by userspace, 
I've been toying with the idea of a "scripted" API that userland could 
use (I actually implemented a "scripted" API for kernel drivers 
originally, but it was a bit too complicated to use :-)

In any case, I don't want to gate this on the userland API.  I consider 
that piece a moving target at this point, and it really has no direct 
bearing on the API used within the kernel.

         -- Jason R. Thorpe <>