Re: Requesting as a GPIO a pin already used through pinctrl

[Linus Walleij <linus.walleij@xxxxxxxxxx>]

On Fri, Sep 16, 2016 at 3:58 PM, Maxime Ripard
<maxime.ripard@xxxxxxxxxxxxxxxxxx> wrote:

> However, things are getting weird when you have that requested pin
> assigned to one device, and you try to export the GPIO on that pin
> (through sysfs for example,

DON'T use sysfs. Use the new chardev ABI which is by the way enabled
by default.

(But you will face the same issue there I guess.)

> but given the implementation, I think that
> it would work alike by calling gpiod_request).

Yes

> In this case, you get no error, and the GPIO is indeed exported,
> allowing the user to change the direction and / or value of the pin,
> taking away that pin from its device.

If and only if the pin controller does not specify .strict in
struct pinmux_ops.

> I have the feeling that the core should prevent that, making sure that
> the gpiod_request returns EBUSY in such a case, but I'm not really
> sure whether it's the case or not, and if it is, where that check is
> happening.

- Did you try specifying .strict for the pinmux?

- Did you read Documentation/pinctrl.txt, section titled
  "GPIO mode pitfalls"?

Yours,
Linus Walleij
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