Re: DMA memory limitation?

From: Jeff Garzik (
Date: Fri Jul 06 2001 - 10:39:57 EST

Steffen Persvold wrote:
> > pci_alloc_* is designed to support ISA.
> >
> > Pass pci_dev==NULL to pci_alloc_* for ISA devices, and it allocs GFP_DMA
> > for you.

> Sure, but the IA64 platforms that are out now doesn't have an IOMMU, so bounce buffers are
> used if you don't specify GFP_DMA in your get_free_page.
> (pci_alloc_consistent() allocates a buffer with GFP_DMA on IA64),

The important thing is that pci_alloc_consistent and the other PCI DMA
functions work as advertised on IA64. If you pass NULL to
pci_alloc_consistent, IA64 should give you an ISA DMA-able address. If
you don't, you get a 32-bit PCI DMA address. Use of GFP_DMA is a
arch-specific detail, so don't let me confuse you there.

Jeff Garzik      | A recent study has shown that too much soup
Building 1024    | can cause malaise in laboratory mice.
MandrakeSoft     |
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This archive was generated by hypermail 2b29 : Sat Jul 07 2001 - 21:00:18 EST