Re: [libgpiod] Some thoughts following a brief test of libgpiod ver 2.1

[Kent Gibson <warthog618@gmail.com>]

On Wed, Jan 03, 2024 at 01:51:53AM -0600, Seamus de Mora wrote:
> On Thu, Dec 28, 2023 at 3:29 AM Kent Gibson <warthog618@gmail.com> wrote:
> >
> > On Wed, Dec 27, 2023 at 07:19:54PM -0600, Seamus de Mora wrote:
> > > Hello,
> > >
> > > I've done some testing/evaluation of the 'libgpiod ver 2.1', and I'd
> > > like to share a few thoughts from that experience.
> > > <snip>
>
> > Then you might want to update your kernel - the kernel device driver was
> > changed to support peristing [1].
> >
> > I get this on my Pi4 running bookworm:
> >
> > $ gpioset -t0 GPIO23=0
> > $ gpioinfo GPIO23
> > gpiochip0 23    "GPIO23"                output
> > $ gpioget -a GPIO23
> > "GPIO23"=inactive
> > $ gpioinfo GPIO23
> > gpiochip0 23    "GPIO23"                output
> > $ gpioset -t0 GPIO23=1
> > $ gpioget -a GPIO23
> > "GPIO23"=active
>
> Yes - the device driver on my bulleye is current; that change was
> committed back in 1Q 2023 IIRC...
>
> I hope I've not already asked this, but:
> In ver 1.6.X of libgpiod, gpioset exits immediately, and returns to
> the bash prompt. The GPIO line remains set at the value designated
> after gpioset exits. AIUI, the driver change from 1Q 2023 was
> responsible for this.
>
> In ver 2.1 of libgpiod, gpioset (without options) does not exit. This
> means there is no return to the bash prompt. The GPIO line still
> remains set at the designated value, so there is no change in the
> behavior of the GPIO line between ver 1.6.X and 2.1.
>
> My question is why does the un-optioned gpioset ver 2.1 not exit - as
> it did in ver 1.6.X?
>

You did, and I answered on SE.
But to reiterate; gpioset v1 exited immediately and that caused
confusion when the driver would revert the line to its default state.
That made it look like gpoioset wasn't doing anything or was generating
a glitch.
That results in "gpioset doesn't work" bug reports, and we got tired of
that.
The decision was to make it block by default to make it clearer that you
lose control over the line when it exits.

In short, we changed it because people complained about it, either
explicitly or implicitly.

The -t0 option can be used to emulate the v1 behaviour.

Cheers,
Kent.