On Thu, Jul 7, 2016 at 12:30 PM, Dirk Behme [off-list ref] wrote:

From: Oleksij Rempel <redacted>

The device tree is the only source of board dependent information in
the system, and thus it is the logical place to list which GPIOs, ADC
channels etc. to use for various functions.  It is straight-forward to
use this information in kernel space and the contents of the device
tree can also be exported to user space.

If user space applications need to use GPIOs, they can do so over the
existing sysfs interface and they could use the device tree
information to find out which GPIO pin to use for a given function,
but unfortunately the numbering of GPIOs exported through sysfs is
totally unrelated to the device tree standard for how references to
GPIO pins are made.  This patch creates a virtual device which is used
to provide symbolic links to GPIO pins in sysfs using logical names
taken from the device tree.

Signed-off-by: Jonas Oester <redacted>
Cc: devicetree@vger.kernel.org
Cc: linux-gpio@vger.kernel.org

NACK! But a year ago it would have been a completely valid reasoning.

In kernel v4.6 I introduced a GPIO character device, and since v4.7
it is possible to name lines from the device tree using gpio-names
like I do in this patch:
http://marc.info/?l=linux-arm-kernel&m=146672328215354&w=2

For the kernel v4.8 merge window I am also adding ABIs to hammer
GPIOs up/down and to listen for GPIO events using the character
device.

Just checkout linux-next, go to tools/gpio and enjoy the new stuff
from userspace as it was designed by the example of lsgpio,
gpio-hammer and gpio-event-mon.

Yours,
Linus Walleij