Getting Memory Map of Every Device in Linux

How to find the memory map of a device?

If it's a PCI device, lspci -vvv will show you.

You can also check /proc/iomem and /proc/ioport for memory and port mappings, respectively.

How to access physical addresses from user space in Linux?

You can map a device file to a user process memory using mmap(2) system call. Usually, device files are mappings of physical memory to the file system.
Otherwise, you have to write a kernel module which creates such a file or provides a way to map the needed memory to a user process.

Another way is remapping parts of /dev/mem to a user memory.

Edit:
Example of mmaping /dev/mem (this program must have access to /dev/mem, e.g. have root rights):

#include <stdio.h>
#include <stdlib.h>
#include <fcntl.h>
#include <sys/mman.h>
#include <unistd.h>

int main(int argc, char *argv[]) {
    if (argc < 3) {
        printf("Usage: %s <phys_addr> <offset>\n", argv[0]);
        return 0;
    }

    off_t offset = strtoul(argv[1], NULL, 0);
    size_t len = strtoul(argv[2], NULL, 0);

    // Truncate offset to a multiple of the page size, or mmap will fail.
    size_t pagesize = sysconf(_SC_PAGE_SIZE);
    off_t page_base = (offset / pagesize) * pagesize;
    off_t page_offset = offset - page_base;

    int fd = open("/dev/mem", O_SYNC);
    unsigned char *mem = mmap(NULL, page_offset + len, PROT_READ | PROT_WRITE, MAP_PRIVATE, fd, page_base);
    if (mem == MAP_FAILED) {
        perror("Can't map memory");
        return -1;
    }

    size_t i;
    for (i = 0; i < len; ++i)
        printf("%02x ", (int)mem[page_offset + i]);

    return 0;
}

mapping a memory region from kernel

You need to remap the memory region with something like ioremap() after you have requested it.

Then, as Tsyvarev and others mentioned, create and export a function in your "parent" driver that returns the mapped memory.

Here is some rough code:

void * mapped_mem;

void * map_addr(unsigned int phy_addr, char * name) {

    struct resource * resource;
    void * mapped_mem;

    resource = request_mem_region(phy_addr, page_size * 4, name);
    // check for errors

    mapped_mem= ioremap_nocache(phy_addr, page_size * 4);
    // check for errors
    return mappedMem;

    //handle errors
}

void * get_mapped_addr(void) {
    return mapped_mem
}

EXPORT_SYMBOL( get_mapped_addr);

Now, mapped_mem should actually be tracked as part of your devices private info, but I figure thats beyond the scope of the question. Also, make sure to check for all possible errors. Make sure that request_mem_region() returns something >0 and not Null.

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