Re: SPI TX andRX buffer overlap

[David Brownell <david-b-yBeKhBN/0LDR7s880joybQ@public.gmane.org>]

On Friday 14 November 2008, Ned Forrester wrote:
> David Brownell wrote:
> > Mapping any number of times *should* be OK -- unless one mapping
> > reports an error.  Or you do them in the wrong order (removing
> > cache entries before writing their data out to memory).
> 
> BINGO!  That was it.

Good news!  I haven't lost it yet.  ;)


> pxa2xx_spi has always done 
> 
> dma_map_single(..., rx, ..., DMA_FROM_DEVICE)
> 
> (thus invalidating the cache) before
> 
> dma_map_single(..., tx, ..., DMA_TO_DEVICE)
> 
> (thus copying possibly invalid data, if the buffers overlapped).
> 
> Thanks, it works now with a much more pleasant patch.

Yeah, mostly just swapping two blocks of code.  Much nicer.


> I never looked at 
> it that way before.  A patch will be coming soon.

Worth auditing the other SPI controller drivers too.  That'd
be easy to get wrong.  Hmmm ... au1550 and iMX goof it too,
while atmel_spi and omap2_mcspi get it right.  Wouldn't you
know ... the only DMA capable SPI drivers I used in DMA mode
don't have this problem.  ;)

- Dave
 
 
> -- 
> Ned Forrester                                       nforrester-/d+BM93fTQY@public.gmane.org
> Oceanographic Systems Lab                                  508-289-2226
> Applied Ocean Physics and Engineering Dept.
> Woods Hole Oceanographic Institution          Woods Hole, MA 02543, USA
> http://www.whoi.edu/sbl/liteSite.do?litesiteid=7212
> http://www.whoi.edu/hpb/Site.do?id=1532
> http://www.whoi.edu/page.do?pid=10079
> 
> 



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