Re: [PATCH v2 1/4] gpiolib: Add "unknown" direction support

[Wolfram Sang]

On Mon, Feb 21, 2011 at 12:07:27PM +0100, Alexander Stein wrote:
> On Monday 21 February 2011, 10:47:56 Wolfram Sang wrote:
> > > We had exported our 5V_enable gpio to sysfs to allow a user-space
> > > application to enable/disable devices connected to 5V circuit.
> > > But on the other hand we had to read the current status of this gpio in
> > > the power-fail interrupt handler to distinguish between false-positive
> > > (5V disabled) and a correct detection.
> > 
> > What about gpio_export() (description in Documentation/gpio.txt)?
> 
> Ah, I didn't know about this. I just expected this is only used from sysfs 
> part. But you have to make sure your .ko is loaded before userspace is 
> accessing sysfs and tries to export the GPIO.

Eh? Userspace doesn't export the GPIO in that case.

> Or is it "allowed" by the API convention to gpio_request and gpio_export (and 
> set direction) a GPIO in the machine startup code which will later be used in 
> a different place?

different place = userspace? Well, that's the main intention of
gpio_export(). (I have the feeling we are missing each other here,
thoguh) I'd suggest looking a bit further in the docs/code. It should
make clear what is possible.

Regards,

   Wolfram

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