Re: [Patch v2 1/2] gpio: add GPIO hogging mechanism

Alexandre Courbot
2014-12-04T15:00:48Z

On Thu, Dec 4, 2014 at 11:52 PM, Maxime Ripard
<maxime.ripard@free-electrons.com> wrote:
> Hi again,
>
> It looks like I missed some part of it.
>
> On Thu, Dec 04, 2014 at 11:15:38PM +0900, Alexandre Courbot wrote:
>> > GPIO hogging needs to be the ideal solution for that, since we can
>> > just enforce the GPIO14 value as the driver is probed, which provides
>> > the guarantee that any driver using the bank B will actually drive the
>> > GPIO it might use.
>>
>> At this point I start wondering if such initial setup should not be
>> the job of the bootloader? GPIO hogging ought to be simple and
>> definitive, adding the possibility to have it just as an initial value
>> would considerably complexify it. E.g. when is the gpio chip driver
>> supposed to release the hogged descriptor in such a case?
>
> Relying on the bootloader for such trivial (and critical) things may
> not work at all. You don't always have the option to replace it,
> either because you physically can't, or just because you don't have
> any alternative.
>
> I agree that in general this is something that should go in the
> bootloader, but we should have a way to deal with the case where it's
> not done.
>
>> Note that if the multiple GPIO consumer feature we are planning goes
>> through, you should be able to use both hogging *and* a regulator on
>> the same GPIO and achieve what you want. The expectation of multiple
>> consumers is that the board designers know what they are doing, and
>> this case would certainly fit (chip hogs the line and doesn't touch
>> the value after that, letting the regulator control it without any
>> conflict afterwards), although it would of course be better to solve
>> the issue through regular probing...
>
> If such an effort is on-going, then I'm totally fine waiting for it
> and leaving that outside the hogging mechanism. As long as it works,
> I'm happy.

Ok. I just want to wait until the next -rc1 to make sure that the
large GPIO array removal patch (on which the multiple consumers
feature depend) did not break anything important, then I will submit
it.