mapping a memory region from kernel

Question

I have a register which needs to be accessed from more then one driver. It is a global read-only register resides in FPGA space The register address is exported via device tree. The first call to "request_mem_region" is ok, but any consecutive call fails.

Is there a way to share a register between drivers ?

Linux Kernel release is 4.14 , using petalinux

Thanks, Ran

Answer 1

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.