Re: [PATCH v3] ad7877: keep dma rx buffers in seperate cache lines

[Mike Frysinger]

On Mon, May 10, 2010 at 17:22, Andrew Morton wrote:
> On Mon, 10 May 2010 12:42:34 +0200 "Oskar Schirmer" wrote:
>> With dma based spi transmission, data corruption
>> is observed occasionally. With dma buffers located
>> right next to msg and xfer fields, cache lines
>> correctly flushed in preparation for dma usage
>> may be polluted again when writing to fields
>> in the same cache line.
>>
>> Make sure cache fields used with dma do not
>> share cache lines with fields changed during
>> dma handling. As both fields are part of a
>> struct that is allocated via kzalloc, thus
>> cache aligned, moving the fields to the 1st
>> position and insert padding for alignment
>> does the job.
>
> This sounds odd. ÂDoesn't it imply that some code somewhere is missing
> some DMA synchronisation actions?

i think it's kind of dumb and induces this sort of bug
semi-frequently, but it is what the current DMA API requires (see like
Documentation/spi/spi-summary)
-mike
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