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

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+ Christoph

On Tue, 3 Dec 2019 11:33:15 +0800 Jun Nie wrote:

> 
> 
> Jisheng Zhang <Jisheng.Zhang@xxxxxxxxxxxxx> 于2019年12月3日周二 上午10:47写道:
> >
> > On Mon,  2 Dec 2019 22:41:04 +0800 Jun Nie wrote:
> >
> >  
> > >
> > >
> > > DMA memory cannot cross specific boundary for some SDHCI controller,
> > > such as DesignWare SDHCI controller. Add DMA memory boundary dt
> > > property and workaround the limitation.  
> >
> > IMHO, the workaround could be implemented in each SDHCI host driver.
> >
> > 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, 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.

Thanks

> controllers. I prefer
> his suggestions.
> 
> Jun





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