how to get the physival address
hji at netscreen.com
Fri Apr 6 02:58:46 EST 2001
>Yes, if I use kmalloc is OK, either __pa or virt_to_phys will return the
>But it does not work for defined variable (it was defined in driver so it
>should be in kernel space, isn't it?). I wonder which memory space, this
>variable belong to?
My 2 cents:
Given that ONLY 2 alternatives you can use for memory allocation when
working with kernel, which
are kmalloc and vmalloc, you are facing different memory usages:
Before talking further, you may have realized:
>From 0xC0000000 to 0XC0000000 + physical_memory_size is 1:1 mapped to
0x000000~physical memory size-1.
Surely, kernel also manages virtual memory from 0XC0000000 +
physical_memory_size + 8M hole to 4G
Therefore, if you used kmalloc to allocate memory, surely, you will easily
find: virtual address-3G is the physical address. However, for vmalloc, the
case is otherwise. The reason now is clear: That virtual address is very
probably from 0XC0000000 + physical_memory_size + 8M hole to 4G. This is
REALLY dynamic. Kernel's vmalloc, just like libc malloc, will go through the
free_area to find a first-bit(libc malloc is not first fit) block for you.
Anyway, back to your question. Your variable is in a memory space after 3G.
But it is byond the 3G+physical_memory_size + 8M. For example, your machine
have a 256M memory, so your variable virtual address is possible:
** Sent via the linuxppc-embedded mail list. See http://lists.linuxppc.org/
More information about the Linuxppc-embedded