I am running linux 2.4.2 on Apple G4 machine. I think the 'PCI bus
addresses' and 'physical addresses' are same on this architecture. I
expected the two be different but according to asm/io.h 'virt_to_bus(addr)
= virt_to_phys(addr) + PCI_DRAM_OFFSET'. I printed the value of
'PCI_DRAM_OFFSET' and that come out to be zero. Is this correct?
If I somehow get the physical address of a user space buffer in a module
and take this as a PCI bus address, will I be able to do DMA properly?
thanks,
Daljeet.
[email protected] writes:
> I am running linux 2.4.2 on Apple G4 machine. I think the 'PCI bus
> addresses' and 'physical addresses' are same on this architecture. I
> expected the two be different but according to asm/io.h 'virt_to_bus(addr)
> = virt_to_phys(addr) + PCI_DRAM_OFFSET'. I printed the value of
> 'PCI_DRAM_OFFSET' and that come out to be zero. Is this correct?
>
> If I somehow get the physical address of a user space buffer in a module
> and take this as a PCI bus address, will I be able to do DMA properly?
virt_to_bus() and bus_to_virt() are deprecated interfaces and should
not be used by anything new. See Documentation/DMA-mapping.txt for
details.
Later,
David S. Miller
[email protected]
[email protected] writes:
> I am running linux 2.4.2 on Apple G4 machine. I think the 'PCI bus
> addresses' and 'physical addresses' are same on this architecture. I
They are the same on an Apple G4 but not necessarily on other PowerPC
machines. It depends on the PCI host bridge implementation.
> expected the two be different but according to asm/io.h 'virt_to_bus(addr)
> = virt_to_phys(addr) + PCI_DRAM_OFFSET'. I printed the value of
> 'PCI_DRAM_OFFSET' and that come out to be zero. Is this correct?
Yes, for an Apple G4.
> If I somehow get the physical address of a user space buffer in a module
> and take this as a PCI bus address, will I be able to do DMA properly?
Yes, on an Apple G4. If you use virt_to_bus then it should work on
all PowerPC machines that I know of (that run 32-bit PPC/Linux). But
as Dave points out, you should use the interfaces described in
Documentation/DMA-mapping.txt instead if at all possible. It's quite
possible that virt_to_bus will be removed during 2.5.x development.
Paul.
On Tue, Jul 03, 2001 at 12:18:58AM -0700, David S. Miller wrote:
>
> [email protected] writes:
> > I am running linux 2.4.2 on Apple G4 machine. I think the 'PCI bus
> > addresses' and 'physical addresses' are same on this architecture. I
> > expected the two be different but according to asm/io.h 'virt_to_bus(addr)
> > = virt_to_phys(addr) + PCI_DRAM_OFFSET'. I printed the value of
> > 'PCI_DRAM_OFFSET' and that come out to be zero. Is this correct?
> >
> > If I somehow get the physical address of a user space buffer in a module
> > and take this as a PCI bus address, will I be able to do DMA properly?
>
> virt_to_bus() and bus_to_virt() are deprecated interfaces and should
> not be used by anything new. See Documentation/DMA-mapping.txt for
> details.
What about non-PCI devices? The IBM 405GP on-chip ethernet controller
is not PCI. It isn't in the standard kernel yet, but I am sure there
are other things that do DMA that aren't PCI.