Re: Reserving a fixed physical address page of RAM.

From: Jon Ringle
Date: Mon Nov 27 2006 - 22:37:27 EST


Robert Hancock wrote:
Jon Ringle wrote:
Hi,

I need to reserve a page of memory at a specific area of RAM that will
be used as a "shared memory" with another processor over PCI. How can I
ensure that the this area of RAM gets reseved so that the Linux's memory
management (kmalloc() and friends) don't use it?

Some things that I've considered are iotable_init() and ioremap().
However, I've seen these used for memory mapped IO devices which are
outside of the RAM memory. Can I use them for reseving RAM too?

I appreciate any advice in this regard.

Sounds to me like dma_alloc_coherent is what you want..

It looks promising, however, I need to reserve a physical address area that is well known (so that the code running on the other processor knows where in PCI memory to write to). It appears that dma_alloc_coherent returns the address that it allocated. Instead I need something where I can tell it what physical address and range I want to use.

Jon
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