Re: [PATCH 5/9] PCI: host: brcmstb: add dma-ranges for inbound traffic

[Christoph Hellwig]

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?