On Mon, 30 Jul 2018 03:11:59 +0000
Matthew Leon [off-list ref] wrote:

 >> Hey Jisheng,  

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Hi,  

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In LKML, we'd better not top post.  

Noted. My apologies.

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Shouldn't we be splitting until all DMA blocks are less than 128M  

boundary?

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I am a noob, but I think we should be prepared for boundaries that when
split in two, will still be greater than 128M. Feel free to disagree but
please explain why I may be wrong. Thank-you.  

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the limitation is "DMA addr can't span 128MB boundary" rather than "must be
less than 128MB", they are different.  

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And the max transfer size of one DMA desc is 64KB.  

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thanks  

I have misspoken. What if the DMA transfer size is 1024M? If we split in
two, then we have 2 transfers, each of which span 512M. So wouldn't we need
to split again to have 4 transfers, each of which span 128M?

the max transfer size of each desc is 64KB, how could it be 1024MB?