[PATCH] gpiolib: allow exporting gpios with custom names

[PATCH] gpiolib: allow exporting gpios with custom names

[Alexey Ignatov]

This allows exporting gpio pins to sysfs with custom names. Before
this patch only gpiochip-supplied names was used, or generic gpio%d.
Added gpiod_export_name() and gpio_export_name() functions.
gpio_request_one() now uses new behaviour with 'label' as gpio name.

Signed-off-by: Alexey Ignatov <lexszero@gmail.com>
---
 drivers/gpio/gpiolib-sysfs.c  | 16 +++++++++++++++-
 drivers/gpio/gpiolib.h        |  1 +
 include/asm-generic/gpio.h    |  6 ++++++
 include/linux/gpio/consumer.h |  2 ++
 4 files changed, 24 insertions(+), 1 deletion(-)

diff --git a/drivers/gpio/gpiolib-sysfs.c b/drivers/gpio/gpiolib-sysfs.c
index 5f2150b..7c56a50 100644
--- a/drivers/gpio/gpiolib-sysfs.c
+++ b/drivers/gpio/gpiolib-sysfs.c
@@ -561,7 +561,9 @@ int gpiod_export(struct gpio_desc *desc, bool direction_may_change)
 	spin_unlock_irqrestore(&gpio_lock, flags);
 
 	offset = gpio_chip_hwgpio(desc);
-	if (desc->chip->names && desc->chip->names[offset])
+	if (desc->ioname)
+		ioname = desc->ioname;
+	else if (desc->chip->names && desc->chip->names[offset])
 		ioname = desc->chip->names[offset];
 
 	dev = device_create(&gpio_class, desc->chip->dev, MKDEV(0, 0),
@@ -602,6 +604,18 @@ fail_unlock:
 }
 EXPORT_SYMBOL_GPL(gpiod_export);
 
+int gpiod_export_name(struct gpio_desc *desc, bool direction_may_change,
+		const char *name)
+{
+	if (!desc) {
+		pr_debug("%s: invalid gpio descriptor\n", __func__);
+		return -EINVAL;
+	}
+	desc->ioname = name;
+	return gpiod_export(desc, direction_may_change);
+}
+EXPORT_SYMBOL_GPL(gpiod_export_name);
+
 static int match_export(struct device *dev, const void *data)
 {
 	return dev_get_drvdata(dev) == data;
diff --git a/drivers/gpio/gpiolib.h b/drivers/gpio/gpiolib.h
index 9db2b6a..9df4bcf 100644
--- a/drivers/gpio/gpiolib.h
+++ b/drivers/gpio/gpiolib.h
@@ -64,6 +64,7 @@ extern struct list_head gpio_chips;
 
 struct gpio_desc {
 	struct gpio_chip	*chip;
+	const char			*ioname;
 	unsigned long		flags;
 /* flag symbols are bit numbers */
 #define FLAG_REQUESTED	0
diff --git a/include/asm-generic/gpio.h b/include/asm-generic/gpio.h
index c1d4105..7957b22 100644
--- a/include/asm-generic/gpio.h
+++ b/include/asm-generic/gpio.h
@@ -123,6 +123,12 @@ static inline int gpio_export(unsigned gpio, bool direction_may_change)
 	return gpiod_export(gpio_to_desc(gpio), direction_may_change);
 }
 
+static inline int gpio_export_name(unsigned gpio, bool direction_may_change,
+		const char *name)
+{
+	return gpiod_export_name(gpio_to_desc(gpio), direction_may_change, name);
+}
+
 static inline int gpio_export_link(struct device *dev, const char *name,
 				   unsigned gpio)
 {
diff --git a/include/linux/gpio/consumer.h b/include/linux/gpio/consumer.h
index 12f146f..2f4c129 100644
--- a/include/linux/gpio/consumer.h
+++ b/include/linux/gpio/consumer.h
@@ -324,6 +324,8 @@ static inline int desc_to_gpio(const struct gpio_desc *desc)
 #if IS_ENABLED(CONFIG_GPIOLIB) && IS_ENABLED(CONFIG_GPIO_SYSFS)
 
 int gpiod_export(struct gpio_desc *desc, bool direction_may_change);
+int gpiod_export_name(struct gpio_desc *desc, bool direction_may_change,
+		const char *name);
 int gpiod_export_link(struct device *dev, const char *name,
 		      struct gpio_desc *desc);
 int gpiod_sysfs_set_active_low(struct gpio_desc *desc, int value);
-- 
1.8.5.3

Re: [PATCH] gpiolib: allow exporting gpios with custom names

[Alexandre Courbot]

Hi,

On Sun, Oct 12, 2014 at 2:45 AM, Alexey Ignatov <lexszero@gmail.com> wrote:
> This allows exporting gpio pins to sysfs with custom names. Before
> this patch only gpiochip-supplied names was used, or generic gpio%d.
> Added gpiod_export_name() and gpio_export_name() functions.

This looks very similar to another proposal that has been posted a few
months ago:

https://lkml.org/lkml/2014/7/23/537

There has been a lenghty discussion about the merits/drawbacks of
doing this instead of using gpiod_export_link(). To summarize my
opinion on the matter, I *really* think using gpiod_export_link() is a
better solution since it puts the GPIO under its owner's /sysfs node,
instead of having totally unrelated GPIOs arbitrarily named under
/sys/class/gpio. IIRC Linus was not too enthusiastic neither.

Could you explain why you think this change is needed, how you plan to
make use of it, and why you cannot use gpiod_export_link() to do the
same?

> gpio_request_one() now uses new behaviour with 'label' as gpio name.

Doesn't this mean that drivers that used gpio_request_one() to export
a GPIO might see the exported name change all of a sudden? This might
make a few people unhappy (also, I could not see this change in your
patch, but only had a quick look).