How to access GPIO from kernel space? (zynq-microzed board) - linux-kernel

Question

I am using zynq-microzed board and I want to access GPIO with kernel space.
Can anyone please tell me how can i attempt doing this?

Answer 1

*NOTE: This is from the Zynq-7000. I believe it's largely the same.
Assuming you're using a devicetree, this is an example entry (in the devicetree):
gpio-device {
compatible = "gpio-control";
gpios = <&gpio0 54 0>; //(Add 32 to get the actual pin number. This is GPIO 86)
};
And you need to state in the driver that you're compatible with the devicetree entry (look at other drivers to see where to put this line):
.compatible = "gpio-control"
In your driver, include #include <linux/gpio.h> and read the pin from the devicetree:
struct device_node *np = pdev->dev.of_node;
int pin;
pin = of_get_gpio(np, 0);
if (pin < 0) {
pr_err("failed to get GPIO from device tree\n");
return -1;
}
Request the use of the GPIO:
int ret = gpio_request(pin, "Some name"); //Name it whatever you want
And set it's direction:
int ret = gpio_direction_output(pin, 0); //The second parameter is the initial value. 0 is low, 1 is high.
Afterwards, set the value like so:
gpio_set_value(pin, 1);
For input:
ret = gpio_direction_input(pin);
value = gpio_get_value(pin);
Free the GPIO when you're finished with it (including on error!):
gpio_free(pin);
At the end of the day, a good method is to grep around the kernel to find drivers that do what you want. In fact grep -r gpio <<kernel_source>> will tell you everything in this answer and more.

Answer 2

Check the following link: enter link description here
Summarizing:
There is an include file for working with GPIOs:
#include <linux/gpio.h>
GPIOs must be allocated before use:
int gpio_request(unsigned int gpio, const char *label);
And GPIO can be returned to the system with:
void gpio_free(unsigned int gpio);
Configure GPIO as Input/Output:
int gpio_direction_input(unsigned int gpio);
int gpio_direction_output(unsigned int gpio, int value);
Operations:
int gpio_get_value(unsigned int gpio);
void gpio_set_value(unsigned int gpio, int value);
Regards.