Re: SPI controller bugfixes needed (full duplex + DMA, data corruption)

[Sascha Hauer <s.hauer-bIcnvbaLZ9MEGnE8C9+IrQ@public.gmane.org>]

Hi David,

On Sat, Nov 15, 2008 at 02:22:32PM -0800, David Brownell wrote:
> Hi,
> 
> We recently turned up a bug in the pxa2xx SPI driver, which
> turns out to also be present in the spi_imx.c and au1550_spi.c
> drivers too.
> 
> Briefly, full duplex transfers are allowed to share the
> same buffer (or partially overlap it), which means that
> the dma mapping operations must be done in a safe order:
> 
>  - first map the TX buffer, so cache data gets written
>    to memory where the DMA will pick it up;
> 
>  - then map the RX buffer, so that cache entries (with
>    soon-to-be-stale data) get removed.
> 
> Doing it the other order, as is done with spi_imx and
> with au1550_spi, causes data corruption by discarding
> data from the cache *before* writing it to memory.
> 
> If you can do it, it'd be good to see this fixed before
> the 2.6.28 kernel ships.

Hm, this is a non trivial fix. I don't have a MX1 based hardware with
something on the SPI bus handy, so this would be a shot in the dark for
me. I hope Andrea jumps in, otherwise we'll have to wait till the driver
works on MX2.

Sascha

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