[PATCH v2] gpio: Allow hogged gpios to be requested

[PATCH v2] gpio: Allow hogged gpios to be requested

[Markus Pargmann]

It can be useful to claim hogged gpios later, for example from
userspace. This allows to set defaults for GPIOs using the hogging
mechanism and override the setup later from userspace or a kernel driver.

This patch adds a check for hogged gpios to allow requesting them. If
the gpio is not hogged but marked as requested, it still fails with
-EBUSY.

Signed-off-by: Markus Pargmann <mpa@pengutronix.de>
---

Only change is, that it is separated from the other series now.

 drivers/gpio/gpiolib.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/gpio/gpiolib.c b/drivers/gpio/gpiolib.c
index 926a1507431f..0f1d1f5faf5d 100644
--- a/drivers/gpio/gpiolib.c
+++ b/drivers/gpio/gpiolib.c
@@ -830,7 +830,8 @@ 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;
 	} else {
-- 
2.1.4

Re: [PATCH v2] gpio: Allow hogged gpios to be requested

[Linus Walleij]

On Tue, Aug 4, 2015 at 11:27 AM, Markus Pargmann <mpa@pengutronix.de> wrote:

> It can be useful to claim hogged gpios later, for example from
> userspace. This allows to set defaults for GPIOs using the hogging
> mechanism and override the setup later from userspace or a kernel driver.
>
> This patch adds a check for hogged gpios to allow requesting them. If
> the gpio is not hogged but marked as requested, it still fails with
> -EBUSY.
>
> Signed-off-by: Markus Pargmann <mpa@pengutronix.de>

To me it feels like a new DT property "gpio-inital-value" or so
need to be defined in addition to the hogging bindings, and that
one just sets the GPIO up without setting the FLAG_IS_HOGGED.

The mechanism needs to be available to non-DT as well
of course, but it could be a first usecase.

So instead of:

line_b {
           gpio-initval;
           gpios = <6 0>;
           output-low;
};

Note: no line-name. And it shouldn't be allowed: we don't
know who will use this in the end.

Yours,
Linus Walleij

Re: [PATCH v2] gpio: Allow hogged gpios to be requested

[Markus Pargmann]

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Hi,

On Mon, Aug 10, 2015 at 11:26:49AM +0200, Linus Walleij wrote:
> On Tue, Aug 4, 2015 at 11:27 AM, Markus Pargmann <mpa@pengutronix.de> wrote:
> 
> > It can be useful to claim hogged gpios later, for example from
> > userspace. This allows to set defaults for GPIOs using the hogging
> > mechanism and override the setup later from userspace or a kernel driver.
> >
> > This patch adds a check for hogged gpios to allow requesting them. If
> > the gpio is not hogged but marked as requested, it still fails with
> > -EBUSY.
> >
> > Signed-off-by: Markus Pargmann <mpa@pengutronix.de>
> 
> To me it feels like a new DT property "gpio-inital-value" or so
> need to be defined in addition to the hogging bindings, and that
> one just sets the GPIO up without setting the FLAG_IS_HOGGED.
> 
> The mechanism needs to be available to non-DT as well
> of course, but it could be a first usecase.
> 
> So instead of:
> 
> line_b {
>            gpio-initval;
>            gpios = <6 0>;
>            output-low;
> };
> 
> Note: no line-name. And it shouldn't be allowed: we don't
> know who will use this in the end.

Sounds good to me. If everyone is okay with this I could go ahead and
implement something like this.

Best Regards,

Markus

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