gpiolib: Document that GPIO line names are not globally unique

gpiochip_set_desc_names() no longer rejects GPIO line name collisions.
Hence GPIO line names are not guaranteed to be globally unique.
In case of multiple GPIO lines with the same name, gpio_name_to_desc()
will return the first match found.

Update the comments for gpio_name_to_desc() and
gpiochip_set_desc_names() to match reality.

Fixes: f881bab038 ("gpio: keep the GPIO line names internal")
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Link: https://lore.kernel.org/r/20200511101828.30046-1-geert+renesas@glider.be
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>

drivers/gpio/gpiolib.c

@@ -296,6 +296,9 @@ static int gpiodev_add_to_list(struct gpio_device *gdev)
 
 /*
  * Convert a GPIO name to its descriptor
+ * Note that there is no guarantee that GPIO names are globally unique!
+ * Hence this function will return, if it exists, a reference to the first GPIO
+ * line found that matches the given name.
  */
 static struct gpio_desc *gpio_name_to_desc(const char * const name)
 {
@@ -329,10 +332,12 @@ static struct gpio_desc *gpio_name_to_desc(const char * const name)
 }
 
 /*
- * Takes the names from gc->names and checks if they are all unique. If they
- * are, they are assigned to their gpio descriptors.
+ * Take the names from gc->names and assign them to their GPIO descriptors.
+ * Warn if a name is already used for a GPIO line on a different GPIO chip.
  *
- * Warning if one of the names is already used for a different GPIO.
+ * Note that:
+ *   1. Non-unique names are still accepted,
+ *   2. Name collisions within the same GPIO chip are not reported.
  */
 static int gpiochip_set_desc_names(struct gpio_chip *gc)
 {