gpiod_get() - How to get GPIO from chip & offset?

[Andy Shevchenko]

On Sun, Aug 7, 2022 at 4:57 PM Ian Pilcher <arequipeno at gmail.com> wrote:
>
> I am trying to figure out how to use gpiod_get(), or one of its
> variants, to get the descriptor (struct gpio_desc *) for a specific
> GPIO.  Getting a reference to the GPIO chip (struct gpio_chip *) is
> straightforward, and it provides a pointer to the device (.parent), but
> I absolutely cannot figure out what I am supposed to pass as the
> *con_id* argument.

Ah, looking into your driver code [1] I think you need to a) switch to
use existing GPIO driver, which is gpio-ich.c in your case and b) use
GPIO lookup tables, you may look at Simatech latest development on how
to achieve that. It uses some Intel chips and LEDs that are connected
to GPIOs.

> I know the offset of the GPIO on the chip, but I can't figure out how to
> use that.

And you don't need to use GPIO offset, whatever it means. What you
need is to have a relative number of GPIO to the chip, so GPIO chip +
relative offset will uniquely give you the line.

> Ultimately, my goal is to set the direction of the GPIO from within a
> "board setup" module.
>
>
> BACKGROUND
>
> I maintain an out-of-tree "board" module[1] that sets up the GPIOs and
> LEDs on my Thecus NAS.  I am in the process of upgrading the OS on the
> NAS, which will require me to change the user-space daemon from the old
> sysfs GPIO interface to the new (non-ancient?) gpiod interface.
>
> One significant difference between the sysfs and gpiod interfaces, is
> that the new interface does not seem to provide an easy way to set a
> GPIO's direction (input/output) from a shell script[2].  Thus, I would
> like the board module to do that, along with the other setup.
>
> [1] https://github.com/ipilcher/n5550/blob/master/modules/n5550_board.c

Why not try to upstream this?

-- 
With Best Regards,
Andy Shevchenko