Re: gpiod: Set pullup for Input Line

[Kent Gibson <warthog618@gmail.com>]

On Tue, Mar 22, 2022 at 10:50:30AM +0200, Andy Shevchenko wrote:
> On Tue, Mar 22, 2022 at 10:39 AM Hans Kurscheidt <lve0200@gmail.com> wrote:
> > Am 22.03.2022 um 09:36 schrieb Hans Kurscheidt:
> > > Am 22.03.2022 um 01:59 schrieb Kent Gibson:
> 
> ...
> 
> > > Still 1 more question. I understand the sense of a Pull-up in Input
> > > mode, but reading the code, I see that the Bias option exists as well
> > > for gpioset (Output). What is the sense of this, and what does it do?
> 
> I guess we started providing OPEN SOURCE / DRAIN in libgpiod v2.0
> (Bart or Kent may correct me), but you should get an idea why it may
> be useful.
> 

No - open drain/source is not new - it has been there since cdev was added
AFAIAA.
The v2 ABI, which libgpiod v2 will support, adds debounce, event sequence
numbers, events from multiple lines in one request, and a few other
things, but the drive options have always been there - even before the
bias options were added.

> On top of that, the pin can be reconfigured from input to output and
> vice versa at run-time. So, keeping a bias setting will allow not to
> think about it when pin direction is switched, although I agree this
> may not be a clean case to use.
> 

Agreed - I would set both the direction and bias in such a case.

Cheers,
Kent.