Re: [PATCH 4/4] mmc: sdhci: Add DMA memory boundary workaround

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On Tue, Dec 03, 2019 at 09:05:23AM +0000, Jisheng Zhang wrote:
> > >
> > > eg. drivers/mmc/host/sdhci-of-dwcmshc.c
> > >  
> > Thanks for the suggestion! Christoph's suggestion can prevent the the issue
> > from the block layer, thus the code can be shared across all
> 
> To be honest, I did consider similar solution from block layer, I.E set
> the seg_boundary_mask, when submitting the workaround last year, but per
> my understanding, SDHCI limitation is the physical DMA addr can't span one
> specific boundary,

As in exactly one boundary and not an alignment?  Where the one
boundary is not a power of two and thus can't be expressed?


> so setting seg_boundary_mask w/ blk_queue_segment_boundary
> can't work. I'm not sure I understand blk_queue_segment_boundary() properly.
> May Christoph help to clarify?
> 
> From another side, drivers/ata/libata-sff.c also workaround the 64K phy DMA
> boundary limitation itself rather than from block layer.

As far as I can tell that workaround should use the segment boundary
setting as well.



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