Re: [libgpiod] Simplify GPIO monitoring

[Bartosz Golaszewski <brgl@xxxxxxxx>]

On Wed, Dec 13, 2023 at 5:50 PM Kyle Nieman <Kyle.Nieman@xxxxxxxxxx> wrote:
>
> Hello,
>
> In embedded linux systems, GPIO monitoring for edge-events is common.
> For example, OpenBMC has several applications/packages that monitor GPIOs for an
> extended period of time.
>
> phosphor-gpio-monitor:
>         1. Starts a systemd service on GPIO events
>         2. Sets a dbus property based upon initial state and on GPIO events
> https://github.com/openbmc/phosphor-gpio-monitor
>
> x86-power-control:
>         1. Controls system power based on different button presses
> https://github.com/openbmc/x86-power-control
>
> However, there seems to be a lot of duplicate code between these applications
> related to monitoring in general that looks like it could be reduced.
>
> GPIO monitoring tends to have the following steps:
> 1. Configure/set up the GPIO line for monitoring
> 2. Read the initial value of GPIO line
> 3. Take action based upon initial value
> 4. Wait for event by monitoring fd
> 5. Take action on event, then continue monitoring or cleanup
>
> A function could internally complete the common steps regardless of what GPIO
> line is being monitored such as steps 1, 2, and 4. The other steps unique to the
> GPIO being monitored could be handled by callbacks. The
> gpiod_ctxless_event_monitor functions seemed to do this partially, but were
> removed along with the rest of the ctxless functions in commit
> 9b6e6d268671ef2dd00d9a9abe7ba43d14e7a84b
> (ctxless: drop all context-less interfaces).
> https://git.kernel.org/pub/scm/libs/libgpiod/libgpiod.git/commit/?id=9b6e6d268671ef2dd00d9a9abe7ba43d14e7a84b
>
> Would there be an issue with adding a higher level abstraction to simplify GPIO
> monitoring?
>

I have decided for libgpiod v2 to remain as low-level and simple as
possible and to only implement the bare minimum of functionality that
at the same time covers all uAPI features.

I'm working on DBus bindings for libgpiod v2 a part of which is a GLib
abstraction layer that is a higher-level C interface. Could you give
it a try and see if it works for your use-case?

    https://github.com/brgl/libgpiod-private/tree/topic/dbus

You can build it using --enable-bindings-glib with configure.

If that's something useful, I could possibly release it separately
from the DBus daemon.

Bart

> Thanks,
> Kyle
>