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Date:   Tue, 21 Aug 2018 16:50:22 -0700
From:   Alex Feinman <>
Subject: Re: Contiguous DMA buffer view for a custom device (Intel/x86)

Thanks, this sounds like what I need. However, since this is a
custom-purpose system, I am tempted to go with CMA and simply
preallocated 200MB on start

On Mon, Aug 20, 2018 at 1:58 PM Alan Cox <> wrote:
> > b) IOMMU can solve this problem for me by providing a device-specific
> > contiguous view of a fragmented physical memory allocation
> > c) In order to enable IOMMU do the above, I need to allocate DRHDs and
> > DMARs in BIOS initialization (I build my own BIOS)
> Yes. The EDK2 firmware toolkit has all the bits you need in it I think.
> isn't quite on the topic you want but it does explain it fairly well in
> passing.
> is a bit out of date but may help too.
> > Please, let me know if I am on the right track? Of course I realize that
> > implementing SGDMA would be the best option, but short of that and blocking
> > out some physical memory on boot, what are my options?
> If performance is absolutely critical simply stealing a chunk of memory
> in the firmware and describing it your device some other way is ugly, but
> for a custom solution I guess anything goes 8)
> Alan

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