From: David Daney <[email protected]>
When we have a GPIO pin connected to an open-drain network, we want a
standard way of specifying this in the device tree. So we choose bit
1 of the flag field to indicate open drain.
A typical use case would be something like:
enum of_gpio_flags f;
.
.
.
reset_gpio = of_get_named_gpio_flags(node, "reset", 0, &f);
.
.
.
ret = gpio_request_one(reset_gpio,
(f & OF_GPIO_OPEN_DRAIN) ? GPIOF_OPEN_DRAIN : 0,
"reset");
.
.
.
gpio_direction_output(reset_gpio, 1);
gpio_set_value(reset_gpio, 0);
msleep(20);
gpio_set_value(reset_gpio, 1);
.
.
.
Signed-off-by: David Daney <[email protected]>
---
include/linux/of_gpio.h | 1 +
1 file changed, 1 insertion(+)
diff --git a/include/linux/of_gpio.h b/include/linux/of_gpio.h
index f14123a..0e374774 100644
--- a/include/linux/of_gpio.h
+++ b/include/linux/of_gpio.h
@@ -30,6 +30,7 @@ struct device_node;
*/
enum of_gpio_flags {
OF_GPIO_ACTIVE_LOW = 0x1,
+ OF_GPIO_OPEN_DRAIN = 0x2,
};
#ifdef CONFIG_OF_GPIO
--
1.7.11.7
On Tue, Feb 11, 2014 at 7:05 AM, David Daney <[email protected]> wrote:
> From: David Daney <[email protected]>
>
> When we have a GPIO pin connected to an open-drain network, we want a
> standard way of specifying this in the device tree. So we choose bit
> 1 of the flag field to indicate open drain.
>
> A typical use case would be something like:
>
> enum of_gpio_flags f;
> .
> .
> .
> reset_gpio = of_get_named_gpio_flags(node, "reset", 0, &f);
> .
> .
> .
> ret = gpio_request_one(reset_gpio,
> (f & OF_GPIO_OPEN_DRAIN) ? GPIOF_OPEN_DRAIN : 0,
> "reset");
> .
> .
> .
> gpio_direction_output(reset_gpio, 1);
> gpio_set_value(reset_gpio, 0);
> msleep(20);
> gpio_set_value(reset_gpio, 1);
This is also useful for gpiod_get(). However, while you are at it,
could you also add a flag for the OF_GPIO_OPEN_SOURCE property? My joy
would be complete if you could also take the time to update
of_find_gpio() to pass these new flags back to the caller as it
already does for OF_GPIO_ACTIVE_LOW.
Then you could even switch your use-case to the gpiod interface and
not bother with passing these flags by yourself anymore. Just sayin'.
;)
Thanks,
Alex.
On 02/10/2014 08:31 PM, Alexandre Courbot wrote:
> On Tue, Feb 11, 2014 at 7:05 AM, David Daney <[email protected]> wrote:
>> From: David Daney <[email protected]>
>>
>> When we have a GPIO pin connected to an open-drain network, we want a
>> standard way of specifying this in the device tree. So we choose bit
>> 1 of the flag field to indicate open drain.
>>
>> A typical use case would be something like:
>>
>> enum of_gpio_flags f;
>> .
>> .
>> .
>> reset_gpio = of_get_named_gpio_flags(node, "reset", 0, &f);
>> .
>> .
>> .
>> ret = gpio_request_one(reset_gpio,
>> (f & OF_GPIO_OPEN_DRAIN) ? GPIOF_OPEN_DRAIN : 0,
>> "reset");
>> .
>> .
>> .
>> gpio_direction_output(reset_gpio, 1);
>> gpio_set_value(reset_gpio, 0);
>> msleep(20);
>> gpio_set_value(reset_gpio, 1);
>
> This is also useful for gpiod_get(). However, while you are at it,
> could you also add a flag for the OF_GPIO_OPEN_SOURCE property? My joy
> would be complete if you could also take the time to update
> of_find_gpio() to pass these new flags back to the caller as it
> already does for OF_GPIO_ACTIVE_LOW.
>
> Then you could even switch your use-case to the gpiod interface and
> not bother with passing these flags by yourself anymore. Just sayin'.
> ;)
Thanks for the suggestion. I will send a revised patch set for your
consideration.
David Daney
On Mon, Feb 10, 2014 at 11:05 PM, David Daney <[email protected]> wrote:
> From: David Daney <[email protected]>
>
> When we have a GPIO pin connected to an open-drain network, we want a
> standard way of specifying this in the device tree. So we choose bit
> 1 of the flag field to indicate open drain.
This is a good idea.
But the patch is missing two things:
- Add open source as well, as indicated.
- Add this definition to include/dt-bindings/gpio/gpio.h
- Add this *and* the missing active low property to the binding
documentation in:
Documentation/devicetree/bindings/gpio/gpio.txt
(pls help with this!)
Yours,
Linus Walleij