On Wed, Jul 06, 2016 at 11:34:37AM +0200, Linus Walleij wrote:

On Tue, Jul 5, 2016 at 8:04 PM, Uwe Kleine-König
[off-list ref] wrote:

quoted

root@hostname:/sys/bus/gpio/devices ls -l
lrwxrwxrwx    1 root     root             0 Jul  5 20:52 gpiochip0 -> ../../../devices/platform/soc/53f00000.aips/53f9c000.gpio/gpiochip0
lrwxrwxrwx    1 root     root             0 Jul  5 20:52 gpiochip1 -> ../../../devices/platform/soc/53f00000.aips/53fa4000.gpio/gpiochip1
lrwxrwxrwx    1 root     root             0 Jul  5 20:52 gpiochip2 -> ../../../devices/platform/soc/53f00000.aips/53fcc000.gpio/gpiochip2
lrwxrwxrwx    1 root     root             0 Jul  5 20:52 gpiochip3 -> ../../../devices/platform/soc/53f00000.aips/53fd0000.gpio/gpiochip3

That is we have:

        Hardware name | software gpiochip
            GPIO4     |      gpiochip0
            GPIO3     |      gpiochip1
            GPIO1     |      gpiochip2
            GPIO2     |      gpiochip3

I bet that's the probe order because when sorted by address (and so
by order in the device tree) we have exactly this ordering. (Compare
with $(grep gpio@ arch/arm/boot/dts/imx25.dtsi).)

That is super-unintuitive for a human user, I agree 100%.

quoted

For a new interface this is OK, still I predict users will complain if
the numbers used don't match naturally the hardware names. And IMHO they
are right.

I agree, and I think that if aliases can alleviate the situation we should
allow them and encourage them. They are the best duct-tape we can
find for the DT systems.

Unfortunately it is not my call, because DT bindings and alias use
is not under my jurisdiction.

I *THINK* the view of the device core maintainers is that udev
and sysfs hierarchies should be used to uniquely identify a certain
device, and that relying on device numbering is too fragile.

I thought the whole idea (or at least a large part of) the new
user-space interface was to allow lookups by line names precisely in
order not to have to rely on gpio numbers, which may not only change
between boots, but also between hardware revisions, etc.

What's wrong with naming the pins in DT and use that for lookups?

I've been too busy with other stuff this spring to follow the new
user-space interface development, but I assume that this had been taken
into account in the design?

Thanks,
Johan
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