Re: [PATCH mmc-next v3 3/3] mmc: sdhci-of-dwcmshc: solve 128MB DMA boundary limitation

[Jisheng Zhang]

On Mon, 30 Jul 2018 03:11:59 +0000
Matthew Leon <matthewleon@xxxxxxxxx> wrote:

>  >> Hey Jisheng,  
> 
> >Hi,  
> 
> >>  
> 
> >In LKML, we'd better not top post.  
> 
> Noted. My apologies.
> 
> >> Shouldn't we be splitting until all DMA blocks are less than 128M  
> boundary?
> >> 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.  
> 
> >the limitation is "DMA addr can't span 128MB boundary" rather than "must be
> >less than 128MB", they are different.  
> 
> >And the max transfer size of one DMA desc is 64KB.  
> 
> >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?