Non-cacheable memory

Dan Malek dan at
Wed Aug 15 07:26:41 EST 2001

Peter Desnoyers wrote:

> This seems like another case of either too little abstraction, or too
> much.  An embedded PPC system with PCI basically has two buses, with
> different DMA addressing, and there's no way to tell consistent_alloc(),
> etc. about that.

Well, if you are using PCI devices, you should be calling the pci_*
versions of these functions.  Those include a pci_dev structure, so
you can get the information you need to do this correctly, and seems
like the solution (more discussion later in the message).

> If you wouldn't mind, could you give me a pointer to the discussion of
> this phase-out?

I hear it from other folks on ppc-dev or something.  There are too many
lists for me to read and find this information first hand :-).

> I wonder if the proper thing to do is to enhance consistent_alloc to
> take an argument indicating the bus type?

Yep.  Like I said above, you should be using the pci_* versions of
these functions.  We can extract information from the pci_dev and pass
it along to consistent_alloc.  The local, internal peripherals can just
pass a NULL or zero or something, whatever this parameter is supposed to
mean.  Or, perhaps the pci_* functions fix up the information returned
from consistent_alloc.

> ....  There are more elegant ways
> of doing things, but this wouldn't involve changes to a lot of code.

This seems elegant enough to me :-).

	-- Dan

** Sent via the linuxppc-embedded mail list. See

More information about the Linuxppc-embedded mailing list