gpiolib: add gpio_array_to_id helper to get ID out of GPIO array

Some boards provide a board version and/or ID coded by pull-up/down
resistors connected to the gpio pins (or pins which can be multiplexed
at some point as gpio). In this case every one implements own gpio id
reader function.

To avoid it, provide the common helper function to extract a value out
of provided gpio array.

Signed-off-by: Oleksij Rempel <o.rempel@pengutronix.de>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>

1 files changed, 31 insertions, 0 deletions

diff --git a/drivers/gpio/gpiolib.c b/drivers/gpio/gpiolib.c
index 27674af54c..6088cadd8a 100644
--- a/drivers/gpio/gpiolib.c
+++ b/drivers/gpio/gpiolib.c
@@ -381,6 +381,37 @@ void gpio_free_array(const struct gpio *array, size_t num)
 }
 EXPORT_SYMBOL_GPL(gpio_free_array);
 
+int gpio_array_to_id(const struct gpio *array, size_t num, u32 *val)
+{
+	u32 id = 0;
+	int ret, i;
+
+	if (num > 32)
+		return -EOVERFLOW;
+
+	ret = gpio_request_array(array, num);
+	if (ret)
+		return ret;
+
+	/* Wait until logic level will be stable */
+	udelay(5);
+	for (i = 0; i < num; i++) {
+		ret = gpio_is_active(array[i].gpio);
+		if (ret < 0)
+			goto free_array;
+		if (ret)
+			id |= 1UL << i;
+	}
+
+	*val = id;
+	ret = 0;
+
+free_array:
+	gpio_free_array(array, num);
+	return ret;
+}
+EXPORT_SYMBOL(gpio_array_to_id);
+
 static int gpiochip_find_base(int start, int ngpio)
 {
 	int i;