Memory-Mapped IO Interface Driver
(c)2014 Joe Balough <[email protected]>

The Memory-Mapped IO Driver can be used to get a userspace sysfs interface
to mmio provided by your SOC or a GPMC-Connected Microcontroller.

At the moment, there is no cmdline or device tree interface to this driver
so it is only useful to add it as a driver then use the mmio_classdev_register
function to register mmio devices on the system.

Here is an example:

Define an array of mmio_entries 
struct mmio_entry entries[] = {
	{.name = "entry_3", .mask = BIT(2), .flags = MMIO_ENTRY_RW },
	{.name = "entry_2", .mask = BIT(1), .flags = MMIO_ENTRY_RW },
	{.name = "entry_1", .mask = BIT(0), .flags = MMIO_ENTRY_RW },
};

Define a mmio_clasdev
struct mmio_classdev my_mmio = {
	.name    = "mmio_group_1",
	.size    = 2,
	.offset  = 0,
	.entries = &entries,
	.num_entries = ARRAY_SIZE(entries),
};

In an init function, remap the memory you need to use. Something like this:
void __init mmio_init(void)
{
	unsigned long base;
	void *reg;
	
	gpmc_cs_request(4, 0x100, &base);
	reg = ioremap_nocache(base, 0x100);
	my_mmio.base = reg;
}

Register the classdev in a fs_initcall() function. Something like this:
int __init mmio_register(void)
{
	mmio_classdev_register(NULL, &my_mmio);
}
fs_initcall(mmio_register);