Mapping physical addresses to virtual address linux

Question

I am working on a small embedded system. When my linux boots up into user space, I know where are my devices in the physical memory. I want to map them into user space virtu

Answer 1

What you are trying to do is accessing what is called IO memory. I can only encourage you to read the Linux Device Drivers (LDD) book and more specifically the chapter 9.

To "allocate" such an area, you need to call

struct resource *request_mem_region(unsigned long start, unsigned long len, char *name)

. Before your driver can access it, you have to assign it a virtual address, this is done with a call to

void *ioremap(unsigned long phys_addr, unsigned long size)

To ensure that your driver will then work on different architectures/platforms, be sure to use some accessor function to such areas ( ioread8/16/32 or iowrite8/16/32 and all of their variants).

Answer 2

In Kernel module, remap_pfn_range() can be used to convert the physical address to virtual address. When you don't have a actual devices you can: 1) create a virtual device and, 2) use mmap to those virtual devices to access the very same kernel memory through remap_pfn_range virtual mapping of that process. 3) Usually in dedicated environments you may addition want to pin those physical pages lest they are taken away from your process. 4) You also share these physical addresses with different processes but will need to handle synchronization, independently through other IPC mechanisms as to each process they will look as different addresses.

Answer 3

In Kernel module, remap_pfn_range() can be used to convert the physical address to virtual address. The following link will be helpful.

How remap_pfn_range remaps kernel memory to user space?