Re: DMA memory limitation?

From: Alan Cox (
Date: Fri Jul 06 2001 - 06:08:51 EST

> A problem arises on 64 bit platforms (such as IA64) if your PCI card is only 32bit (can
> address the first 4G) and you don't wan't to use bounce buffers. If you use GFP_DMA on

GFP_DMA is ISA dma reachable, Forget the IA64, their setup is weird and
should best be ignored until 2.5 as and when they sort it out.

> bounce buffers are needed. On Alpha GFP_DMA is not limited at all (I think). Correct me if

Alpha has various IOMMU facilities

> I'm wrong, but I really think there should be a general way of allocating memory that is
> 32bit addressable (something like GFP_32BIT?) so you don't need a lot of #ifdef's in your
> code.

No ifdefs are needed

        GFP_DMA - ISA dma reachable
        pci_alloc_* and friends - PCI usable memory

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This archive was generated by hypermail 2b29 : Sat Jul 07 2001 - 21:00:18 EST