device-tree: at91: irq and gpios: problem while requesting a gpio used as an interrupt source.

[Linus Walleij]

On Thu, Jan 23, 2014 at 2:16 PM, Jean-Jacques Hiblot
<jjhiblot at traphandler.com> wrote:

> I've been thinking hard on the gpio ownership and I'd like your
> opinion on the following assumptions:
>
> - a gpio used as an interrupt is always a gpio configured as an input.
> (corollary : a gpio used for interrupt cannot not be an ouput)

That is the assumption made by the core. Until the day someone
comes up with a weird usecase...

> - a gpio used as an input or interrupt only, could be safely accessed
> by multiple users.

Multiple consumers is the term we would use. But yes.

> - a gpio used as an output should be used as such by only one user.
> Still other users should be allowed to read its value.

Sounds reasonable.

> If those assumptions are true, I believe they can lead to a new
> exclusion scheme:
> - ouput is mutually exclusive with interrupt but not with input
> - only 1 ouput user at a time.

Logical conclusion from the above yes.

> It would do away with our sharing issue and more (chained interrupt
> handlers on gpio interrupt, read/interrupt access through sysfs to a
> gpio requested by a driver)
>
> And I believe that most of the infrastructure is in place to implement this :
> - direction flags in gpio_request_one
> - gpio_lock_as_irq/gpio_unlock_as_irq

So I think what I need to see is a proposed patch, whether it will
hit a particular driver or the gpiolib core, but either would probably
be interesting.

Pls keep linux-gpio and Alexandre on CC for this discussion.

Yours,
Linus Walleij