Re: [libgpiod] bug: pull-up does not work

[Kent Gibson <warthog618@xxxxxxxxx>]

On Fri, Mar 25, 2022 at 04:13:11PM +0100, Jiří Prchal wrote:
> 
> 
> On 25. 03. 22 15:57, Kent Gibson wrote:
> > On Fri, Mar 25, 2022 at 11:02:07AM +0100, Jiří Prchal wrote:
> > > Hi,
> > > since in debian is 1.6.2 and pull-up doesn't work so I cloned git, branch
> > > next/libgpiod-2.0 and compiled libgpiod and tools, but no luck, same result.
> > > 
> > 
> > You mean it doesn't work for you on your platform.
> > 
> > The libgpiod-2.0 branch is a work in progress and should not be considered
> > the place to go to find solutions to problems with v1.6.
> > Not that I'm saying that the v2 branch doesn't work, I'm actually pretty
> > sure it does, but its purpose is to switch to the latest kernel uAPI, not
> > to provide fixes, should they be needed, for v1.6.
> Just thought api v1 doesn't support pull-ups so tried v2.

v1 does support bias since Linux v5.5, and libgpiod added support in v1.5.

> > 
> > > ~# uname -r
> > > 5.17.0-rc7_cpm9g25
> > > 
> > > floating pins should go with pull-up/down
> > > ~# gpioget -B pull-up 3 6 8 10 12 14 16 18 20
> > > 0 0 0 0 0 0 0 0
> > > ~# gpioget -B pull-up 3 6 8 10 12 14 16 18 20
> > > 1 1 0 0 0 0 0 0
> > > ~# gpioget -B pull-up 3 6 8 10 12 14 16 18 20
> > > 0 1 0 1 0 0 0 0
> > > 
> > > ~# gpioget -v
> > > gpioget (libgpiod) v2.0-devel
> > > 
> > > Whats wrong with it?
> > 
> > You forgot to mention which of those pins are floating.
> All of them.
> > Or what gpiochip3 is and whether it supports biasing.
> AT91SAM9G25, hw supports pull-ups.
> > 
> > So does your chip support pull-up/down?
> > The kernel can only enable it if the hardware and pinctrl driver supports it.
> Is there possibility that pinctrl doesn't support it? I think other gpios
> used in kernel are with pull-up.
> Example:
> pinctrl@fffff400 {
> 	1wire {
> 		pinctrl_1wire: 1wire-0 {
> 			atmel,pins = <AT91_PIOC 0 AT91_PERIPH_GPIO AT91_PINCTRL_PULL_UP>; /* PC0
> PIO, pull-up */
> 		};
> 	};
> };
> 

Pinctrl and device tree are outside my area, but my understanding is
that setting via DT is a separate interface, so while it may be
supported by DT it may not be via the gpiolib interface.
But I will defer to anyone else on that.
(CCing in Andy since I'm pretty sure he would know)

Not sure which pinctrl is relevant for your case.
pinctrl-at91 doesn't appear to support setting the pull-up via the gpiolib
interface, but pinctrl-at91-pio4 does, so my guess would be you are using
the pinctrl-at91.

But again, this is outside my area so you would need to confirm that
yourself or get feedback from someone else.
If you determine that you are using a pinctrl that supports setting
bias via gpiolib then we'll have to do some more digging.

Cheers,
Kent.