gpiolib: Export gpiochip_request_own_desc and gpiochip_free_own_desc

Both functions were introduced to let gpio drivers request their own
gpio pins. Without exporting the functions, this can however only be
used by gpio drivers built into the kernel.

Secondary impact is that the functions can not currently be used by
platform initialization code associated with the gpio-pca953x driver.
This code permits auto-export of gpio pins through platform data, but
if this functionality is used, the module can no longer be unloaded due
to the problem solved with the introduction of gpiochip_request_own_desc
and gpiochip_free_own_desc.

Export both function so they can be used from modules and from
platform initialization code.

Reviewed-by: Alexandre Courbot <acourbot@nvidia.com>
Reviewed-by: Mika Westerberg <mika.westerberg@linux.intel.com>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>

1 files changed, 21 insertions, 0 deletions

diff --git a/Documentation/gpio/driver.txt b/Documentation/gpio/driver.txt
index 224dbbc..18790c2 100644
--- a/Documentation/gpio/driver.txt
+++ b/Documentation/gpio/driver.txt
@@ -167,3 +167,24 @@ is released:
 When implementing an irqchip inside a GPIO driver, these two functions should
 typically be called in the .startup() and .shutdown() callbacks from the
 irqchip.
+
+
+Requesting self-owned GPIO pins
+-------------------------------
+
+Sometimes it is useful to allow a GPIO chip driver to request its own GPIO
+descriptors through the gpiolib API. Using gpio_request() for this purpose
+does not help since it pins the module to the kernel forever (it calls
+try_module_get()). A GPIO driver can use the following functions instead
+to request and free descriptors without being pinned to the kernel forever.
+
+	int gpiochip_request_own_desc(struct gpio_desc *desc, const char *label)
+
+	void gpiochip_free_own_desc(struct gpio_desc *desc)
+
+Descriptors requested with gpiochip_request_own_desc() must be released with
+gpiochip_free_own_desc().
+
+These functions must be used with care since they do not affect module use
+count. Do not use the functions to request gpio descriptors not owned by the
+calling driver.