Re: configuration for nc pins without pull

[Linus Walleij <linus.walleij@xxxxxxxxxx>]

On Sun, Mar 22, 2015 at 11:00 AM, Uwe Kleine-König
<u.kleine-koenig@xxxxxxxxxxxxxx> wrote:

> for a machine I want to configure a pin that is actually not connected
> to minimize floating. (I think this is sensible, isn't it?)

Yup, and Russell gave an excellent summary of why.

> For the pinctrl I can use a hog group of the pinctrl device. At least
> one of the pins doesn't have a pullup/pulldown configuration though, so
> I want to mux it to its gpio function and set the gpio to output and the
> desired value.
>
> Is there something nicer than defining an always-on regulator with gpios
> = <&gpio4 3 0> to accomplish that without additional code?

As explained in
Documentation/pinctrl.txt, section "GPIO mode pitfalls" like 788
this is not really "GPIO", it is a way of controlling the electric state
of the pin using software, it's just the hardware designers idea of the
use case that it is "GPIO", it is not what a software engineer would call
GPIO.

If the controller support GENERIC_PINCONF I suggest implementing
PIN_CONFIG_OUTPUT from include/linux/pinctrl/pinconf-generic.h
which is more or less for exactly this purpose.

It will bring the pin into "GPIO mode" by poking the right registers but
what is really happening is a non-GPIO usecase on the pin control
side of things.

This should be done using a hog on the device tree and
output-low; or output-high; using the generic pinctrl bindings.

Yours,
Linus Walleij
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