[PATCH 2/3] Add support for monitoring gpio switches

On Fri, Dec 4, 2015 at 6:31 PM, Martyn Welch
[off-list ref] wrote:

Select Chromebooks have gpio attached to switches used to cause the
firmware to enter alternative modes of operation and/or control other
device characteristics (such as write protection on flash devices). This
patch adds a driver that exposes a read-only interface to allow these
signals to be read from user space.

This functionality has been generalised to provide support for any device
with device tree support which needs to identify a gpio as being used for a
specific task.

Signed-off-by: Martyn Welch <martyn.welch@collabora.co.uk>

If you want to do this thing, also propose a device tree binding document
for "gpio-switch".

But first (from Documentation/gpio/drivers-on-gpio.txt):

- gpio-keys: drivers/input/keyboard/gpio_keys.c is used when your GPIO line
  can generate interrupts in response to a key press. Also supports debounce.

- gpio-keys-polled: drivers/input/keyboard/gpio_keys_polled.c is used when your
  GPIO line cannot generate interrupts, so it needs to be periodically polled
  by a timer.

- extcon-gpio: drivers/extcon/extcon-gpio.c is used when you need to read an
  external connector status, such as a headset line for an audio driver or an
  HDMI connector. It will provide a better userspace sysfs interface than GPIO.

So you mean none of these apply for this case?

Second: what you want to do is export a number of GPIOs with certain names
to userspace. This is something very generic and should be implemented
as such, not as something Chromebook-specific.

Patches like that has however already been suggested, and I have NACKed
them because the GPIO sysfs ABI is insane, and that is why I am refactoring
the world to create a proper chardev ABI for GPIO instead. See:
http://marc.info/?l=linux-gpio&m=144550276512673&w=2

So for the moment, NACK on this, please participate in creating the
*right* ABI for GPIO instead of trying to shoehorn stuff into the dying
sysfs ABI.

Yours,
Linus Walleij