Re: [PATCH 3/9] gpio: Allow hogged gpios to be requested

[Uwe Kleine-König <u.kleine-koenig@xxxxxxxxxxxxxx>]

Hello Markus,

On Sun, Jul 19, 2015 at 04:01:42PM +0200, Markus Pargmann wrote:
> On Fri, Jul 17, 2015 at 10:27:02PM +0200, Uwe Kleine-König wrote:
> > On Fri, Jul 17, 2015 at 11:32:44AM +0200, Markus Pargmann wrote:
> > > diff --git a/drivers/gpio/gpiolib.c b/drivers/gpio/gpiolib.c
> > > index bf4bd1d120c3..9f402b159cbe 100644
> > > --- a/drivers/gpio/gpiolib.c
> > > +++ b/drivers/gpio/gpiolib.c
> > > @@ -798,7 +798,8 @@ static int __gpiod_request(struct gpio_desc *desc, const char *label)
> > >  	 * before IRQs are enabled, for non-sleeping (SOC) GPIOs.
> > >  	 */
> > >  
> > > -	if (test_and_set_bit(FLAG_REQUESTED, &desc->flags) == 0) {
> > > +	if (test_and_set_bit(FLAG_REQUESTED, &desc->flags) == 0 ||
> > > +	    test_and_clear_bit(FLAG_IS_HOGGED, &desc->flags) == 1) {
> > >  		desc_set_label(desc, label ? : "?");
> > >  		status = 0;
> > I don't like this patch. IMHO hogging is a "use" of a GPIO that should
> > prevent it being requested.
> 
> I disagree with you here. The original patch stated in its description
> that it was designed to initialize GPIOs. In my understanding this does
> not necessarily mean that a hogged GPIO has to be blocked forever.
Assume for a moment I can agree with "not necessarily". But now, what
about the cases where a hogged GPIO should be blocked?
IMHO, if you want to drive the GPIO from userspace anyhow, you don't
need to add a hog for it.

> The IS_HOGGED flag is cleared at the same time it is tested so only one
> consumer can request one hogged GPIO. The GPIO is not considered to be
> hogged after it is normally requested.
You're right here, I missed the and_clear_bit part on the test.

Best regards
Uwe

-- 
Pengutronix e.K.                           | Uwe Kleine-König            |
Industrial Linux Solutions                 | http://www.pengutronix.de/  |
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