Hi,

On Wed, Aug 11, 2010 at 06:57:16PM +0530, Ravi Gupta wrote:

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 :

No, you don't have to modify anything, and yes, you can
use standard kernel GPIO API.

#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");

Before issing gpio_request() you must get GPIO number from the
of_get_gpio() or of_get_gpio_flags() calls (the _flags variant
will also retreive flags such as 'active-low').

The calls assume that you have gpio = <> specifier in the
device tree, see arch/powerpc/boot/dts/mpc8377_rdb.dts's
"leds" node as an example.

As you want GPIO LEDs, you can use drivers/leds/leds-gpio.c
(see of_gpio_leds_probe() call, it gets gpio numbers via
of_get_gpio_flags() and then requests them via gpio_request()).

Also see

Documentation/powerpc/dts-bindings/gpio/gpio.txt
Documentation/powerpc/dts-bindings/gpio/led.txt

    if (ret) {
      printk(KERN_WARNING "sample_driver: unable to request GPIO_PG%d\n",
i);
      //return ret;
    }
  }

  return 0;
}

On Wed, Aug 11, 2010 at 07:49:40PM +0530, Ravi Gupta wrote:

Also, when I try to export a gpio in sysfs

echo 9 > /sys/class/gpio/export

The gpio numbers are global, i.e. GPIO controller base + GPIO
number within the controller.

[...]

drwxr-xr-x    3 root     root            0 Jan  1 00:00 gpiochip192

So, if you want GPIO9 within gpiochip192, you should issue
"echo 201 > export".

Thanks,

-- 
Anton Vorontsov
email: cbouatmailru@gmail.com
irc://irc.freenode.net/bd2