Linux and reading and writing a general purpose 32 bit register - linux-device-driver

Question

I am using embedded Linux for the NIOS II processor and device tree. The GPIO functionality provides the ability to read and or write a single bit at a time. I have some firmware and PIOS that I want to read or write atomically by setting or reading all 32 bits at one time. It seems like there would be a generic device driver that if the device tree was given the proper compatibility a driver would exist that would allow opening the device and then reading and writing the device. I have searched for this functionality and do not find a driver. One existing in a branch but was removed by Linus.
My question is what is the Linux device tree way to read and write a device that is a general purpose 32 bit register/pio?

Answer 1

Your answer is SCULL
Character Device Drivers
You will have to write a character device driver with file operations to open and close a device. Read, write, ioctl, and copy the contents of device.
static struct file_operations query_fops =
{
.owner = THIS_MODULE,
.open = my_open,
.release = my_close,
.ioctl = my_ioctl
};
Map the address using iomem and directly read and write to that address using rawread and rawwrite. Create and register a device as follows and then it can be accessed from userspace:
register_chrdev (0, DEVICE_NAME, & query_fops);
device_create (dev_class, NULL, MKDEV (dev_major, 0), NULL, DEVICE_NAME);
and then access it from userspace as follows:
fd = open("/dev/mydevice", O_RDWR);
and then you can play with GPIO from userspace using ioctl's:
ioctl(fd, SET_STATE);