DT on s3c24xx

Linus Walleij linus.walleij at linaro.org
Thu Dec 18 06:53:14 PST 2014

On Thu, Dec 18, 2014 at 9:34 AM, Vasily Khoruzhick <anarsoul at gmail.com> wrote:

> Can I change pin function after gpio was requested? In low-power state
> (i.e. when display is disabled) it's gpio driving some level,
> and in active state it's some LCD controller pin (don't remember which
> one exactly)

Please read the section named "GPIO mode pitfalls" in
Documentation/pinctrl.txt very closely.

Two ways:

- You can use the GPIO and pin control interface to the same
  hardware in parallel. There is no blocking this since there
  is hardware out that that actually allow this. NOT

- If the "GPIO mode" mentioned is only about e.g. grounding
  the pins in a low power state and then not really about using
  them as GPIO, extend the pin controller to be able to e.g.
  ground the pins with PIN_CONFIG_OUTPUT or
  generic bindings.

If the usecase is low power, the latter approach is recommended.

Linus Walleij

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