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

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Hi Christoph

On Tue, 3 Dec 2019 05:06:09 -0800 Christoph Hellwig wrote:


> 
> On Tue, Dec 03, 2019 at 09:49:49AM +0000, Jisheng Zhang wrote:
> > > 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?  
> >
> > Take drivers/mmc/host/sdhci-of-dwcmshc.c for example, target physical DMA addr
> > can't span 128MB, 256MB, 128*3MB, ...128*nMB
> >
> > I'm not sure whether blk_queue_segment_boundary could solve this limitation.  
> 
> That is exaxtly the kind of limitation blk_queue_segment_boundary is
> intended for.

Until after dma_map_sg(), we can't know the physical DMA address range, so
how does block layer know and check the DMA range beforehand? I'm a newbie on
block layer, could you please teach me? At the same time
I'm reading the code as well.

Thanks in advance





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