[PATCH 3/3] gpio: Add reference counting for non-exclusive GPIOs

[Charles Keepax <ckeepax@opensource.cirrus.com>]

Currently, a GPIO can be requested multiple times when the
NONEXCLUSIVE flag is set, however it must still be freed a single
time. This makes client code rather complex, since multiple drivers
may request the GPIO but only a single one can free it. Rather than
manually handling this in each driver add some basic reference
counting into the core.  Currently, this is fairly primitive but
so is the support for the NONEXCLUSIVE flag and the implementation
covers those use-cases.

Reported-by: Marek Szyprowski <m.szyprowski@samsung.com>
Signed-off-by: Charles Keepax <ckeepax@opensource.cirrus.com>
---
 drivers/gpio/gpiolib.c | 13 ++++++++++++-
 drivers/gpio/gpiolib.h |  2 ++
 2 files changed, 14 insertions(+), 1 deletion(-)

diff --git a/drivers/gpio/gpiolib.c b/drivers/gpio/gpiolib.c
index 230e41562462b..42ba86fb495a5 100644
--- a/drivers/gpio/gpiolib.c
+++ b/drivers/gpio/gpiolib.c
@@ -2407,6 +2407,13 @@ static bool gpiod_free_commit(struct gpio_desc *desc)
 
 	might_sleep();
 
+	if (desc->n_users > 1) {
+		desc->n_users--;
+		return true;
+	} else {
+		desc->n_users = 0;
+	}
+
 	gpiod_unexport(desc);
 
 	spin_lock_irqsave(&gpio_lock, flags);
@@ -4142,7 +4149,8 @@ struct gpio_desc *__must_check gpiod_get_index(struct device *dev,
 			 */
 			dev_info(dev, "nonexclusive access to GPIO for %s\n",
 				 con_id ? con_id : devname);
-			return desc;
+
+			goto done;
 		} else {
 			return ERR_PTR(status);
 		}
@@ -4155,6 +4163,9 @@ struct gpio_desc *__must_check gpiod_get_index(struct device *dev,
 		return ERR_PTR(status);
 	}
 
+done:
+	desc->n_users++;
+
 	return desc;
 }
 EXPORT_SYMBOL_GPL(gpiod_get_index);
diff --git a/drivers/gpio/gpiolib.h b/drivers/gpio/gpiolib.h
index 087d865286a0c..f96eda90281a3 100644
--- a/drivers/gpio/gpiolib.h
+++ b/drivers/gpio/gpiolib.h
@@ -230,6 +230,8 @@ struct gpio_desc {
 	const char		*label;
 	/* Name of the GPIO */
 	const char		*name;
+
+	unsigned int		n_users;
 };
 
 int gpiod_request(struct gpio_desc *desc, const char *label);
-- 
2.11.0