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Date: Fri, 20 Oct 2017 16:57:52 +0200
From: Christoph Hellwig <hch@lst.de>
To: Jim Quinlan <jim2101024@gmail.com>
Subject: Re: [PATCH 5/9] PCI: host: brcmstb: add dma-ranges for inbound traffic
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Cc: Mark Rutland <mark.rutland@arm.com>, Linux-MIPS <linux-mips@linux-mips.org>,
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On Fri, Oct 20, 2017 at 10:41:56AM -0400, Jim Quinlan wrote:
> I am not sure I understand your comment -- the size of the request
> shouldn't be a factor.  Let's look at your example of the DMA request
> of 3fffff00 to 4000000f (physical memory).  Lets say it is for 15
> pages.  If we block out  the last page [0x3ffff000..0x3fffffff] from
> what is available, there is no 15 page span that can happen across the
> 0x40000000 boundary.  For SG, there can be no merge that connects a
> page from one region to another region.  Can you give an example of
> the scenario you are thinking of?

What prevents a merge from say the regions of
0....3fffffff and 40000000....7fffffff?

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