Device or resource busy while configuring gpio as a char device - c

Question

I am trying to configure a GPIO pin as output but it is failing with the reason of device or resource busy. The pin is configured as output, open-drain and belongs to the group of gpiochip24 at offset 3. On reading the information from line info IOCTL I can see that the flag is 3 (OPEN_DRAIN) and is assigned a consumer. But when I try to configure the pin as output with a default value using the GPIO_GET_LINEHANDLE_IOCTL, the IOCTL fails.
int gpioFd = open("/dev/gpiochip24", 0);
if (gpioFd < 0) {
printf("ERROR: GPIO chip fail\n");
return -1;
}
struct gpiohandle_request req;
req.flags |= GPIOHANDLE_REQUEST_OUTPUT;
req.lineoffsets[0] = 3;
req.lines = 1;
req.default_values[0] = 0;
strcpy(req.consumer_label, "P_EN");
int lhfd = ioctl(gpioFd, GPIO_GET_LINEHANDLE_IOCTL, &req);
if(lhfd < 0)
{
int err = errno;
printf("Error No: %d\n", err);
printf("ERROR: Gpio Line handle\n");
return -1;
}
Output:
Error No: 16
ERROR: Gpio Line handle
I looked inside /sys/kernel/debug/gpio to understand who is using the resource but I get the following response:
gpiochip24: GPIOs 99-106, parent: platform/139b0000.pinctrl, gpg2
How do I resolve this error of device busy?

Answer 1

Because req is local, it has garbage when allocated, and it doesn't look like the code is initializing it properly, and - in particular - the flags value probably has junk in it.
req.flags |= GPIOHANDLE_REQUEST_OUTPUT; // no
req.flags = GPIOHANDLE_REQUEST_OUTPUT; // yes
would work around this particular issue, but be sure all the other fields in this structure are not relying on junk.