Re: gpiod: Set pullup for Input Line

[Kent Gibson <warthog618@gmail.com>]

On Tue, Mar 22, 2022 at 09:36:29AM +0100, Hans Kurscheidt wrote:
> 
> Am 22.03.2022 um 01:59 schrieb Kent Gibson:
> > On Mon, Mar 21, 2022 at 07:33:28PM +0200, Andy Shevchenko wrote:
> > > On Mon, Mar 21, 2022 at 7:27 PM Hans Kurscheidt<lve0200@gmail.com>  wrote:
> > > > Hi thanks, that makes hope.
> > > First of all, please do not top-post.
> > > 
> > > > Unfortunately apt-get gpiod on my OrangePi Armbian board gives me
> > > > version 1.2, while the dev is already at 1.6. I probably have to build
> > > > it from source.
> > > > 
> > > > Keeping fingers crossed .
> > > I don't remember the details of old versions of libgpiod (Bart? Kent?)
> > > I think it was available even there.
> > > 
> > Bias support was added in libgpiod v1.5.
> > It wasn't even exposed in the uAPI prior to that - it wasn't added until
> > kernel v5.5.
> > 
> > In this case building the latest stable, 1.6.3, is the way to go.
> > 
> > Cheers,
> > Kent.
> > 
> > > > Am 21.03.2022 um 17:26 schrieb Andy Shevchenko:
> > > > > On Mon, Mar 21, 2022 at 1:30 PM Hans Kurscheidt<lve0200@gmail.com>  wrote:
> > > > > > Despite deep searching, I cannot find any information, if gpiod allow
> > > > > > specifying pull-ups to input lines and how to do/handle it.
> > > > > Have you followed this code from libgpiod?
> > > > > https://git.kernel.org/pub/scm/libs/libgpiod/libgpiod.git/tree/tools/gpioset.c#n44
> > > 
> > > -- 
> > > With Best Regards,
> > > Andy Shevchenko
> 
> Thank-you Kent!
> 
> 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?
> 

As answered by Andy, drive and bias are orthogonal so gpioset supports
setting them independently.  Obviously setting bias with push-pull
doesn't make much sense, but the case it is there for is combining open
drain/source with a pull for when the line is not being driven.
Granted that such a pull would usually be provided externally, but the
option is there in case it isn't.

> WRT. building it, it wasn't that straight forward, as in the description. On
> the Armbian/Debian buster Kernel 5.10.60-sunxi64 #21.08.1 I had to create an
> M4 dir, install GNU-archives and install libtools in addition to succeed
> building it. Then doxygen and help2man were still missing.
> 

I defer to Bart on build issues, but you shouldn't need to create the
m4 directory - you should install m4.
In fact all these packages:
  apt_packages:
      - autoconf
      - autoconf-archive
      - libtool
      - m4
      - doxygen
      - graphviz

That list is drawn from a recent patch I submitted to build the documentation
on a readthedocs Ubuntu VM, but it is probably the same or very similar
for Armbian.
That is in addition to build-essential, but I assume you already have that.

Cheers,
Kent.