Re: [PATCH v2] gpio: add userspace ABI for GPIO line information

[Michael Welling <mwelling@ieee.org>]

On Mon, Feb 15, 2016 at 02:20:35PM +0100, Linus Walleij wrote:
> This adds a GPIO line ABI for getting name, label and a few select
> flags from the kernel.
> 
> This hides the kernel internals and only tells userspace what it
> may need to know: the different in-kernel consumers are masked
> behind the flag "kernel" and that is all userspace needs to know.
> 
> However electric characteristics like active low, open drain etc
> are reflected to userspace, as this is important information.
> 
> We provide information on all lines on all chips, later on we will
> likely add a flag for the chardev consumer so we can filter and
> display only the lines userspace actually uses in e.g. lsgpio,
> but then we first need an ABI for userspace to grab and use
> (get/set/select direction) a GPIO line.
> 
> Sample output from "lsgpio" on ux500:
> 
> GPIO chip: gpiochip7, "8011e000.gpio", 32 GPIO lines
>         line 0: unnamed unlabeled
>         line 1: unnamed unlabeled
> (...)
>         line 25: unnamed "SFH7741 Proximity Sensor" [kernel output open-drain]
>         line 26: unnamed unlabeled
> (...)
> 
> Signed-off-by: Linus Walleij <linus.walleij@linaro.org>

I attempted to test the gpio char implementation on the Dragonboard 410c and it
fails to boot.

I just pulled the linux-gpio/chardev-more branch and built from there. The board
boots from the mainline 4.5-rc2.

If there were any boot messages I would give them to you but it fails early.
Tried to get more from earlycon but still nothing.

Do you have a 64 bit arm target to test this on to see if it fails for you as
well?