On 06/23/2016 12:04 PM, Linus Walleij wrote:

On Wed, Jun 22, 2016 at 6:16 PM, Mark Rutland [off-list ref] wrote:

quoted

In general, our use of aliases is rather ill-defined. It would be nicer
if we could address devices in a similar manner to disks or partitions,
e.g. by path or uuid, but I don't think we have anything sensible we can
use there.

Given that, I can see the use of an alias to provide a consistent way of
referring to a particular gpiochip (and maybe we need to expose the
alises information somehow to userspace), but IMO that's independent of
any global ID space, probe ordering, etc.

 From the kernel point of view the way forward to identify and refer to
a particular gpiochip is using /dev/gpiochipN the character device.

If complete topology of the bus placement etc is needed, userspace
can traverse /sys/bus/gpio/*

This solves the big problem with the current global numbering system
in /sys/class/gpio/*

Hm. May be i misunderstood samthing (and sry, if my following question
is dummy as I've not followed closely new GPIO ABI development), but..

- from above description it seems that  global numbering system is not really
solved :( instead it's been moved one level up and now the same happens with
gpiocipX devices :( Wouldn't it be reasonable to add possibility to create named/labeled
gpiocipX devices from the very beginning, like: "/dev/gpiocipX[_name|label], or "/dev/gpiocip[_name|label]", or ..

Actually, struct gpio_chip has label field already.

PS. From my experience, the worst case with dev numbering usually happens after 
few insmod/rmmod (or sometimes after suspend/resume) iterations - ttyX ;..(.

So what this alias should address would be two things:

- Solve the immediate issue of the global number space for the
   legacy sysfs ABI, but also:

- Determine which chip is gpiochip0, gpiochip1, .. etc in the
   new ABI, so the devices get consistent numbering.

The latter is lightly frowned upon by the udev people: they think it
is more proper to traverse /sys to get topological information about
the devices.

I would appreciate if a patch to add alias handling would take care
of both these things if we apply it.

-- 
regards,
-grygorii