ARM Linux driver : how to write to a physical address?

Did you check how the other device drivers do it? (BTW: The kernel is full of examples).

jbe

H!,

Just type cast the address to a variable and use it. Any thing that is directly mapped to the processors address space can be accssed like that. Also try __raw_read Api, should be available on ARM.

ull

unsigned long *ptr =3D 0xphysicaladdr

This would be wrong on other architectures (I am unfamiliar with ARM but I believe most of them have an MMU and therefore it is wrong there too). Normally you would need a phys_to_virt() to convert the physical address to the virtual address used in the kernel process.

ie

unsigned long *ptr = phys_to_virt( 0xphysicaladdr );

See

Cheers, John McCallum Edinburgh

Uzytkownik "John McCallum" napisal w wiadomosci news:gci1ej$k03$1$ snipped-for-privacy@news.demon.co.uk...

to

Please dont't forget about: volatile. Lot of time I spent, when I was trying to understad WHY :)

volatile unsigned long *ptr = phys_to_virt( 0xphysicaladdr );

Grzegorz Kania Czerwionka, Poland

is

t I

ing

phys_to_virt() only works with directly mapped physical address. I don't think using phys_to_virt() is the best idea, anyway. Usually you do this in several steps in a device driver:

1. Call request_mem_region() to request virtual memory region;
2. Call ioremap() to map physical address to virtual address;
3. Read/write mapped virtual address by using iowriteXX() / ioreadXX(), etc. Here XX can be 8, 16, or 32 for example, represents bit width.
4. Call iounmap() and release_mem_region() to release memory mapping;

Thanks, Marco Wang