Re: status of i2c-cpm and ds2482

[Jean Delvare <khali-PUYAD+kWke1g9hUCZPvPmw@public.gmane.org>]

Hi Baurzhan,

On Sat, 9 Jan 2010 00:19:43 +0100, Baurzhan Ismagulov wrote:
> On Fri, Jan 08, 2010 at 03:06:06PM +0100, Jochen Friedrich wrote:
> > 	I2C0: i2c@860 {
> ...
> > 		w1@aa {
> > 			reg = <0xaa>;
> > 			compatible = "dallas,ds2482";
> > 		};
> > 	};
> 
> This worked, thanks much Jochen and Jean!
> 
> I had to use "reg = <18>;", it didn't build with "0x".
> 
> FWIW, I've also tried restoring 0x18 in normal_i2c in ds2482.c, and
> i2c-core complained about quick not being supported.

Restoring? 0x18 has never been in ds2482's normal_i2c list.

> Where can I read about what it is?

As I2C doesn't offer any standard way to detect device presence at a
given address, we (ab)use the SMBus "Quick command" (0-byte message)
for this purpose. Not all adapters support this type of transaction.

> Why is it now required, whereas this worked in 2.6.25.7?

The i2c-cpm driver was not present in kernel 2.6.25.7, so you must have
been using an out-of-tree driver. Maybe that driver had (possibly fake)
support for the SMBus quick command.

-- 
Jean Delvare
http://khali.linux-fr.org/wishlist.html