How to use mpc8xxx_gpio.c device driver

Question

Hi,

I am new to device driver development. I am trying to access the GPIO of MPC837xERDB eval board. I have upgraded its kernel to linux-2.6.28.9 and enable support for mpc8xxx_gpio.c. On boot up, it successfully detect two gpio controllers. Now my question is how I am going to use it to communicate with the gpio pins? Do I have to modify the code in mpc8xxx_gpio.c file to do whatever I want to do with gpios or I can use the standard gpio API provided in kernel ( gpio_request()/gpio_free() ). I also tries the standard kernel API, but it fails. Here is my code :

#include <linux/module.h>
#include <linux/errno.h>  /* error codes */
#include <linux/gpio.h>

static __init int sample_module_init(void)
{
  int ret;

  int i;
  for (i=1; i<32; i++) {
    ret = gpio_request(i, "Sample Driver");
    if (ret) {
      printk(KERN_WARNING "sample_driver: unable to request GPIO_PG%d\n", i);
      //return ret;
    }  
  }

  return 0;
}

static __exit void sample_module_exit(void)
{
  gpio_free(9);
}

MODULE_LICENSE("GPL");

module_init(sample_module_init);
module_exit(sample_module_exit);

It give the following O/P:

[  617.075329] sample_driver: unable to request GPIO_PG1
[  617.080418] sample_driver: unable to request GPIO_PG2
[  617.085470] sample_driver: unable to request GPIO_PG3
[  617.090522] sample_driver: unable to request GPIO_PG4
[  617.095574] sample_driver: unable to request GPIO_PG5
[  617.100625] sample_driver: unable to request GPIO_PG6
[  617.105676] sample_driver: unable to request GPIO_PG7
[  617.110727] sample_driver: unable to request GPIO_PG8
[  617.115779] sample_driver: unable to request GPIO_PG9
[  617.120830] sample_driver: unable to request GPIO_PG10
[  617.125968] sample_driver: unable to request GPIO_PG11
[  617.131106] sample_driver: unable to request GPIO_PG12
[  617.136245] sample_driver: unable to request GPIO_PG13
[  617.141383] sample_driver: unable to request GPIO_PG14
[  617.146521] sample_driver: unable to request GPIO_PG15
[  617.151660] sample_driver: unable to request GPIO_PG16
[  617.156798] sample_driver: unable to request GPIO_PG17
[  617.161936] sample_driver: unable to request GPIO_PG18
[  617.167074] sample_driver: unable to request GPIO_PG19
[  617.172213] sample_driver: unable to request GPIO_PG20
[  617.177351] sample_driver: unable to request GPIO_PG21
[  617.182489] sample_driver: unable to request GPIO_PG22
[  617.187628] sample_driver: unable to request GPIO_PG23
[  617.192767] sample_driver: unable to request GPIO_PG24
[  617.197905] sample_driver: unable to request GPIO_PG25
[  617.203042] sample_driver: unable to request GPIO_PG26
[  617.208182] sample_driver: unable to request GPIO_PG27
[  617.213319] sample_driver: unable to request GPIO_PG28
[  617.218458] sample_driver: unable to request GPIO_PG29
[  617.223597] sample_driver: unable to request GPIO_PG30
[  617.228735] sample_driver: unable to request GPIO_PG31
[  617.233873] sample_driver: unable to request GPIO_PG32

Can someone provide me a sample code or something else. Actually I am trying to set the GPIO pin no. 9 to active low as it is connected to a LED on board.

Thanks in advance Ravi Gupta

Answer 1

Have you looked into Documentation/gpio.txt in your kernel source?

Answer 2

From your other question:

# ls /sys/class/gpio/ -la
drwxr-xr-x    4 root     root            0 Jan  1 00:00 .
drwxr-xr-x   24 root     root            0 Jan  1 00:00 ..
--w-------    1 root     root         4096 Jan  1 00:10 export
drwxr-xr-x    3 root     root            0 Jan  1 00:00 gpiochip192
drwxr-xr-x    3 root     root            0 Jan  1 00:00 gpiochip224
--w-------    1 root     root         4096 Jan  1 00:00 unexport

You have two blocks of GPIO pins. One block starts at number 192 and the other at 224. In your code above, you are trying to request GPIO 0-31, which don't exist on your platform.

You can find out how many GPIOs are in each block by looking at the ngpio file in each gpiochip* directory.