Hi,
I am working with a PowerPC 405 based asic having PCI_DRAM_OFFSET to be defined
not to be zero.
I was using consistent_alloc to get a memory area to be used by my ethernet
driver for its descriptor tables.
consistent_alloc returned a virtual address and the address on my pci bus. The
address on the bus was
returned correctly, but the mapping consistent_alloc was working was not like I
expected it.
It maps the virtual address to an address on the bus and not to the real
address of my DRAM.
A mapping to the real address in DRAM is, what I wanted to have. I tried to do
a virt_to_phys
on the virtual address, but got, again, the address on the bus. And a
bus_to_phys I could not find ;-)
Now I wondered, how consistent_free could work, since consistent_alloc did a
get_free_pages, but did not store the physical address of that buffer
somewhere. Instead it stored the bus address. I did the following experiment:
TEST TEST TEST ...
DESCR: virt_addr=0xc7b82000 bus_addr=0xf6e6b000
phys_addr=0xf6e6b000 pci_dram_offset=0xf4000000
DESCR: virt_addr=0xc7b82000 bus_addr=0xf6e6a000
phys_addr=0xf6e6a000 pci_dram_offset=0xf4000000
DESCR: virt_addr=0xc7b82000 bus_addr=0xf6e91000
phys_addr=0xf6e91000 pci_dram_offset=0xf4000000
DESCR: virt_addr=0xc7b82000 bus_addr=0xf6e90000
phys_addr=0xf6e90000 pci_dram_offset=0xf4000000
DESCR: virt_addr=0xc7b82000 bus_addr=0xf6e29000
phys_addr=0xf6e29000 pci_dram_offset=0xf4000000
DESCR: virt_addr=0xc7b82000 bus_addr=0xf6e28000
phys_addr=0xf6e28000 pci_dram_offset=0xf4000000
I was wondering if that can be correct, since I am allocating the same amount
of memory all the time and returning it immediatly after doing that. So I would
expect, that the function returns the same physical and bus addresses again,
since I expect it to be deterministic.
After thinking about it I modified consistent_alloc in the following way:
....
/* Allocate some common virtual space to map the new pages.
*/
area = get_vm_area(size, VM_ALLOC);
if (area == 0) {
free_pages(page, order);
return NULL;
}
va = VMALLOC_VMADDR(area->addr);
ret = (void *)va;
/* This gives us the real physical address of the first page.
*/
#if defined(WITH_MY_FIX)
*dma_handle = virt_to_bus(page);
pa = virt_to_phys(page);
#else
*dma_handle = pa = virt_to_bus(page);
#endif
flags = _PAGE_KERNEL | _PAGE_NO_CACHE;
err = 0;
for (i = 0; i < size && err == 0; i += PAGE_SIZE)
err = map_page(va+i, pa+i, flags);
....
Now the returned mapping done to the physical memory instead of the bus
addresses, which I cannot access directly on my system. Now my system can
perform the consistent_free function correctly and it prints:
DESCR: virt_addr=0xc7b82000 bus_addr=0xf6e53000
phys_addr=0x02e53000 pci_dram_offset=0xf4000000
DESCR: virt_addr=0xc7b82000 bus_addr=0xf6e53000
phys_addr=0x02e53000 pci_dram_offset=0xf4000000
DESCR: virt_addr=0xc7b82000 bus_addr=0xf6e53000
phys_addr=0x02e53000 pci_dram_offset=0xf4000000
DESCR: virt_addr=0xc7b82000 bus_addr=0xf6e53000
phys_addr=0x02e53000 pci_dram_offset=0xf4000000
DESCR: virt_addr=0xc7b82000 bus_addr=0xf6e53000
phys_addr=0x02e53000 pci_dram_offset=0xf4000000
DESCR: virt_addr=0xc7b82000 bus_addr=0xf6e53000
phys_addr=0x02e53000 pci_dram_offset=0xf4000000
Which I consider to be ok. If I observed that correctly, consistent_alloc has a
memory leak and strange things may happen if consistent_free is called. Any
opinions on that?
Frank Haverkamp
--
Frank Haverkamp
f.haverkamp at web.de
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