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linux gpio driver can't export GPIO on mpc8308

Question asked by ali tahamia on Sep 22, 2016
Latest reply on Oct 3, 2016 by ali tahamia

I want to use linux GPIO driver to handle one of the GPIO pins of mpc8308 processor as output. so I enabled the GPIO driver and it's debugging in:

Device Drivers ---> GPIO Support ---> /sys/class/gpio/... (sysfs interface)

but when using `echo` command to export GPIO21, it gives Invalid argument errno:

gpio_request: gpio-21 (sysfs) status -22
export_store: status -22

I used `cat /sys/kernel/debug/gpio` to see which GPIO pins are reserved by other drivers, but it shows nothing. so this pin is free.

I hacked the kernel for the place of error and found that in beginning of `gpio_request` function in gpiolib.c it crashes at last line in bellow:


int gpio_request(unsigned gpio, const char *label)
struct gpio_desc *desc;
struct gpio_chip *chip;
int status = -EINVAL;
unsigned long flags;

spin_lock_irqsave(&gpio_lock, flags);

if (!gpio_is_valid(gpio))
goto done;
desc = &gpio_desc[gpio];
chip = desc->chip;
if (chip == NULL)
goto done


`gpio_desc[gpio]` is an entry of an array in driver (`static struct gpio_desc gpio_desc[ARCH_NR_GPIOS];`) that must be initialized by `gpiochip_add` function in driver. and this function must be called early as driver says:

* gpiochip_add() - register a gpio_chip
* @chip: the chip to register, with chip->base initialized
* Context: potentially before irqs or kmalloc will work
* Returns a negative errno if the chip can't be registered, such as
* because the chip->base is invalid or already associated with a
* different chip. Otherwise it returns zero as a success code.
* When gpiochip_add() is called very early during boot, so that GPIOs
* can be freely used, the chip->dev device must be registered before
* the gpio framework's arch_initcall(). Otherwise sysfs initialization
* for GPIOs will fail rudely.
* If chip->base is negative, this requests dynamic assignment of
* a range of valid GPIOs.

but `gpiochip_add` function never is called during boot.

Here is the .dts file:

gpio@c00 {

      device_type = "gpio";
      compatible = "fsl,mpc8315-gpio";
      reg = <0xc00 0x100>; //reg = <0xc00 0x18>;
      interrupt-parent = < &ipic >;


can you help me with this problem?


I changed dts file to this:

gpio1: gpio-controller@c00 {
   #gpio-cells = <2>;
   compatible = "fsl,mpc8308-gpio", "fsl,mpc8349-gpio";
   reg = <0xc00 0x100>;
   interrupt-parent = <&ipic>;
   interrupts = <74 0x8>;
   #interrupt-cells = <2>;

and now it shows `gpiochip224` in `/sys/class/gpio` and this gpiochip has 32 GPIOs. but I don't know what is the mapping between 21 and 224-255?
can anyone tell me what is the relation between PIN numbers in datasheet and GPIO numbers in kernel for MPC8308 PowerPC series processor? I try all numbers 224-255 and none of them works.