Re: [PATCH] gpiolib-legacy: Request gpio without touching direction

[Linus Walleij <linus.walleij@xxxxxxxxxx>]

On Thu, May 24, 2018 at 3:01 PM, Einar Vading <einar.vading@xxxxxxxx> wrote:

Hi Einar,

thanks for your patch!

Unfortunately it can not be applied.

> Adds function to request a gpio without touching the direction of the
> gpio upon export.
>
> This is useful if some user space application know what state the gpio
> should be in and it is important that this state is kept during reboot.
>
> Signed-off-by: Einar Vading <einarv@xxxxxxxx>

The sysfs ABI is deprecated since two years:
https://git.kernel.org/pub/scm/linux/kernel/git/linusw/linux-gpio.git/commit/Documentation/ABI/obsolete/sysfs-gpio?id=fe95046e960b4b76e73dc1486955d93f47276134

This means we do not extend or add features to the sysfs ABI.

The new chardev ABI should be used for all new features to
userspace. Here are the example tools for GPIO descriptor
access:
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/tools/gpio

What is even more featured for commandline and apps is
libgpiod:
https://git.kernel.org/pub/scm/libs/libgpiod/libgpiod.git/

If you want to add a new flag for not touching the direction
of the GPIO when requesting, by patching
include/uapi/linux/gpio.h then I'm all game for that!

We currently have these:
/* Linerequest flags */
#define GPIOHANDLE_REQUEST_INPUT        (1UL << 0)
#define GPIOHANDLE_REQUEST_OUTPUT       (1UL << 1)
#define GPIOHANDLE_REQUEST_ACTIVE_LOW   (1UL << 2)
#define GPIOHANDLE_REQUEST_OPEN_DRAIN   (1UL << 3)
#define GPIOHANDLE_REQUEST_OPEN_SOURCE  (1UL << 4)

We could definately add an "ASIS" flag if you can find a way to
implement it nicely!

Yours,
Linus Walleij
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