gpio: provide and use gpiod_get_label()

We will soon serialize access to the descriptor label using SRCU. The
write-side of the protection will require calling synchronize_srcu()
which must not be called from atomic context. We have two irq helpers:
gpiochip_lock_as_irq() and gpiochip_unlock_as_irq() that set the label
if the GPIO is not requested but is being used as interrupt. They are
called with a spinlock held from the interrupt subsystem.

They must not do it if we are to use SRCU so instead let's move the
special corner case to a dedicated getter.

First: let's implement and use the getter where it's applicable.

Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Acked-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>

drivers/gpio/gpiolib-cdev.c

@@ -2305,8 +2305,8 @@ static void gpio_desc_to_lineinfo(struct gpio_desc *desc,
 		if (desc->name)
 			strscpy(info->name, desc->name, sizeof(info->name));
 
-		if (desc->label)
-			strscpy(info->consumer, desc->label,
+		if (gpiod_get_label(desc))
+			strscpy(info->consumer, gpiod_get_label(desc),
 				sizeof(info->consumer));
 
 		dflags = READ_ONCE(desc->flags);

drivers/gpio/gpiolib.c

@@ -105,6 +105,11 @@ static void gpiochip_irqchip_free_valid_mask(struct gpio_chip *gc);
 
 static bool gpiolib_initialized;
 
+const char *gpiod_get_label(struct gpio_desc *desc)
+{
+	return desc->label;
+}
+
 static inline void desc_set_label(struct gpio_desc *d, const char *label)
 {
 	d->label = label;
@@ -2391,7 +2396,7 @@ char *gpiochip_dup_line_label(struct gpio_chip *gc, unsigned int offset)
 	 *
 	 * Until this happens, this allocation needs to be atomic.
 	 */
-	label = kstrdup(desc->label, GFP_ATOMIC);
+	label = kstrdup(gpiod_get_label(desc), GFP_ATOMIC);
 	if (!label)
 		return ERR_PTR(-ENOMEM);
 
@@ -4732,7 +4737,7 @@ static void gpiolib_dbg_show(struct seq_file *s, struct gpio_device *gdev)
 			is_irq = test_bit(FLAG_USED_AS_IRQ, &desc->flags);
 			active_low = test_bit(FLAG_ACTIVE_LOW, &desc->flags);
 			seq_printf(s, " gpio-%-3d (%-20.20s|%-20.20s) %s %s %s%s\n",
-				   gpio, desc->name ?: "", desc->label,
+				   gpio, desc->name ?: "", gpiod_get_label(desc),
 				   is_out ? "out" : "in ",
 				   value >= 0 ? (value ? "hi" : "lo") : "?  ",
 				   is_irq ? "IRQ " : "",

drivers/gpio/gpiolib.h

@@ -208,6 +208,7 @@ int gpio_set_debounce_timeout(struct gpio_desc *desc, unsigned int debounce);
 int gpiod_hog(struct gpio_desc *desc, const char *name,
 		unsigned long lflags, enum gpiod_flags dflags);
 int gpiochip_get_ngpios(struct gpio_chip *gc, struct device *dev);
+const char *gpiod_get_label(struct gpio_desc *desc);
 
 /*
  * Return the GPIO number of the passed descriptor relative to its chip