Re: libgpiod gpiod_line_request output and keep existing value

[Bartosz Golaszewski <brgl@xxxxxxxx>]

czw., 5 mar 2020 o 15:57 Mark Deneen <mdeneen@xxxxxxxxx> napisał(a):
>
> Is it possible to use gpiod_line_request to set a given line as an
> output but retain the current state of the line?  I can not use
> gpiod_line_get_value to query the state since the line in question has
> not been requested yet.

No, because it doesn't make sense. If you're driving the line, you
define its state.

>
> Let's say that I have a userspace process which sets a gpio to high
> and I restart the process.  I would like for the output to remain high
> when I request the line again in the new process.  This was possible
> with gpiolib+sysfs, is it possible with libgpiod?
>

This was rather a side effect of sysfs keeping the line exported
without any user-space process controlling it. This is not the case
with a character device where if the process exits, all resources are
freed ie. GPIOs are tied to processes rather than to a sysfs
interface.

Best regards,
Bartosz Golaszewski