Kernel, virtual and physical memory

Question

Hi,
I would like to get a clarification of the uses of the terms kernel, virtual and physical memory. Functions like kmem_alloc provide non-paged 'kernel' memory, but is this a pointer to a physical memory address, or is it similar to a virtual address that gets mapped by the memory management when it is referenced like virtual memory?
Is there a way to determine a mapping between a virtual address and a physical address? (like vtophys in bsd or virt_to_phys/virt_to_bus in linux) ?
Is all memory that is normally used within a driver (e.g. messages through a STREAM or DMA areas) 'kernel' memory, and is this a direct physical memory address (as asked above)?
Many thanks
S.

Answer 1

Hi,
Most kernel code and device drivers will only use virtual addresses. Yes, it is right!
But I want to access a specific physical address.
Because the bus bridge chip with PCI bus-master access a specific physical address directly.
My system configuration is below:
Platform: IA32
Address map:
0x00000000 - 0x000FFFFF: Main Memory, VGA Frame Buffer, Boot ROM
0x00100000 - 0x0FFFFFFF : Main Memory(DIMM) - 255MB*
0x10000000 - 0xFEBFFFFF: PCI bus memory space
0xFEC00000 - 0xFFF7FFFF: Not Used
0xFFFF8000 - 0xFFFFFFFF: Boot ROM
*My system has 128MB DIMM on board.
The bus bridge chip access a physical address at 0x06000000.
I tested whether it would be set up correctly by using Linux as follow:
1) Memory size is specified to 96MB compulsorily.
init: Linux mem=96M
2) Access to Physical address space via virtual address in kernel space.
init_module(){
va = iormap(0x06000000, size);
*va = value;
value = *(va+n);
3) work good.
I tried on Solaris by the same way.
But I cannot find working.
1) Memory size is specified to 96MB compulsorily.
In /etc/system:
set physmem=23723 <- Page size is 4K in my system. lower than 96MB.
2) Access to Physical address space via virtual address in kernel space.
xxx_attach(){
ddi_regs_map_setup();
ddi_putX(value);
value = ddi_getX();
driver.conf
name="xxx" class="sysbus" reg=0,0x06000000, size;
And I tried access by using /dev/mem.
This also went wrong.
dose anyone have good idea?
Toru OHATA