[PATCH] regulator: convert to use gpio_desc internally

[Alexandre Courbot]

On Tue, Jul 1, 2014 at 8:10 PM, Mark Brown <broonie at kernel.org> wrote:
> On Tue, Jul 01, 2014 at 09:59:01AM +0900, Alexandre Courbot wrote:
>
>> We could compare on the (dev, func, index) triplet instead of the GPIO
>> number, but that looks a little bit overkill (and won't work if we mix
>> integers and descriptors).
>
> This only works if requests always come from the same triplet - if we're
> requesting in the client context that doesn't work.

Indeed.

>
>> How about we add a SHAREABLE flag to the descriptors that indicates
>> whether a GPIO can be shared. I can then see one of the following two
>> policies being applied:
>
>> 2) GPIOs are shareable by default, and remain that way as long as they
>> are obtained using the gpiod interface exclusively. A call to
>> gpio_to_desc() or gpio_request_one() would mark the GPIO as
>> non-shareable until it is released by the integer interface (and would
>> fail if the GPIO is already requested by gpiod). Any integer interface
>> call on a gpiod-requested GPIO would now simply fail with -EPERM.
>
> This seems sensible to me.
>
>> I am not sure whether 2) covers all the requirements to allow gpiod to
>> be "secure", but if it does, then I suggest we give it a shot
>> (although at least a few drivers will certainly need fixing, but such
>> is life). This would add a very welcome layer of security and
>> guarantee gpiod users that nobody can spoof or mess otherwise with
>> their GPIOs unless the board or firmware designer allows it.
>
> I don't see security as a big deal - so long as normal, well written
> code gets the benefit of the access protection I think we're doing
> enough.  If something jumpst through hoops to bypass it then it's buggy
> but fundamentally we have to trust the kernel to at least some extent.

The security consideration apart, making GPIOs obtained through gpiod
shareable seems to be a good way to solve the issue we are having
here.

Linus, if you agree with the idea I can try to give it a shot sometime
this week.