GPIO offsets used by userspace

[Xo Wang]

On Tue, Jan 31, 2017 at 3:25 PM, Joel Stanley <joel at jms.id.au> wrote:
> On Wed, Feb 1, 2017 at 8:45 AM, Xo Wang <xow at google.com> wrote:
>> However I don't actually see a /sys/class/gpio/gpiochipN directory on
>> the BMCs I touched. Any ideas?
>
> That's strange. On the machines I looked at we do have that. I double
> checked on a Zaius running the v1.99.1 tag:
>
> root at zaius5:~# ls /sys/class/gpio/gpiochip320/
> base       device     label      ngpio      subsystem  uevent
>

So it is! I checked again. Must be a gross malfunction on my part.

>> I mentioned this on GitHub, but in theory we should have at least one
>> /sys/class/gpio/gpiochipN directory, where N is the offset for GPIOs
>> provided by that GPIO device.
>>
>> On a BMC not attached to GPIO expanders this directory name could be
>> parsed by the Python currently in use. Not foolproof, but it could be
>> a working stopgap.
>
> You're right, we could find this one. This would break on Witherspoon
> though which will soon gain a driver for a GPIO expander.
>
> We could write some python to iterate through the gpiochipN
> directories, and match against the label:
>
> root at zaius5:~# cat /sys/class/gpio/gpiochip320/label
> 1e780000.gpio
>
> This would be a stopgap until we could get something saner, like sysfs
> files named after the net or function.
>

Makes sense.

xo