Re: [PATCH 0/6] GPIO character device skeleton

[Arnd Bergmann <arnd@xxxxxxxx>]

On Friday 30 October 2015 15:43:18 Linus Walleij wrote:
> On Sat, Oct 24, 2015 at 8:42 PM, Markus Pargmann <mpa@xxxxxxxxxxxxxx> wrote:
> 
> > What happens if we have two I2C gpio expanders with the same I2C
> > addresses connected to different I2C busses? If I see this correctly
> > they would both show up with the same name. Is there an easy and
> > race-free way to see which GPIO chip is connected to which I2C bus?
> 
> My spontaneous question is: how does ethernet interfaces or whatever
> handle this nowadays to get unique device names?
> 
> Currently we are probe-order dependent. It would be good to fix
> the plug-order business from day 1 but how?

ethernet devices are in their own namespace but can get renamed according
to distro-specific policy. A common method is to keep a record of all
mac addresses that were seen in a file in /etc (e.g.
/etc/udev/rules.d/70-persistent-net.rules) and rename them to whatever
they were previously known as when they show up with a different name.

For character devices, udev has a complex set of (user-overridable) rules
to derive one or more stable name(s) from the sysfs attributes.

	Arnd

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