[libgpiod PATCH] gpioget: Add --line-name to lookup GPIO line

Andrew Jeffery andrew at aj.id.au
Fri Dec 3 17:20:12 AEDT 2021

On Fri, 3 Dec 2021, at 14:20, Zev Weiss wrote:
> On Wed, Dec 01, 2021 at 08:29:47PM PST, Joel Stanley wrote:
>>On Wed, 1 Dec 2021 at 08:29, Bartosz Golaszewski <brgl at bgdev.pl> wrote:
>>> On Wed, Dec 1, 2021 at 8:29 AM Joel Stanley <joel at jms.id.au> wrote:
>>> >
>>> > Systems provide line names to make using GPIOs easier for userspace. Use
>>> > this feature to make the tools user friendly by adding the ability to
>>> > show the state of a named line.
>>> >
>>> >  $ gpioget --line-name power-chassis-good
>>> >  1
>>> >
>>> >  $ gpioget -L pcieslot-power
>>> >  0
>>> I'm not very convinced to be honest. It's not like "gpioget gpiochip0
>>> `gpiofind gpiochip0 line-name`" requires much more typing than
>>> "gpioget gpiochip --line-name=name".
>>I'm taking on feedback from people working in our labs, and
>>implementing userspace applications. We've been building BMCs with
>>mainline Linux for about six years now, and it's been a long road
>>re-training them from "back in the day we just did devmem <this>
>><that>" and "why can't we just do cat /sys/class/gpio/gpio305/value",
>>and now "why does the level of the GPIO change back after I run the
>>This usability improvement is one more step towards them using and
>>being happy with the "new world" of the gpiod API.
>>Once we settle on a good API here, I plan on submitting a version of
>>gpioget/gpioset added to busybox.
>>> There are also other questions:
>>> this uses getopt and only allows to specify a single line name. What
>>> if we want to specify more lines like with offsets? Even if you allow
>>> multiple names, getopt() doesn't guarantee ordering of arguments.
>>If you're happy with the concept I'm happy to iterate on the implementation.
>>Yes, it only allows a single line name. That tends to be how the tool
>>is used, both from the command line and in scripts.
>>Can you give me an example of your proposed command line API, so I can
>>understand what you're suggesting here?
> My two cents: like Jeremy, I would very much welcome the ability to
> specify GPIOs by name instead of number, but the one-line-only
> limitation does seem unfortunate.  How about making a command-line flag
> that just means "line-specifier arguments should be interpreted as names
> instead of numbers"?
> So you could do:
>   $ gpioget --by-name chassis-intrusion cpu1-prochot
>   0 1
>   $ gpioset --by-name led-green=1 led-red=0

I came up with this approach as well (independently, just thinking 
about Joel's patch). I think it has good ergonomics. I hadn't figured 
out how we should interpret the arguments as line index vs line name, 
but your --by-name option solves that. I like it a lot.


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