Re: problem with converting from at91_spi to atmel_spi (AT91RM9200)

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

On Thursday 24 May 2007, Haavard Skinnemoen wrote:
> On Wed, 23 May 2007 09:06:12 -0700
> David Brownell <david-b-yBeKhBN/0LDR7s880joybQ@public.gmane.org> wrote:
> > On Wednesday 23 May 2007, Ivan Kuten wrote:
> > > 	
> > >                 .chip_select    = 0,
> > 
> > Chipselect zero ... I've had one report that this driver has some issues
> > on that chipselect.  There seem to be two errata in conflict here:
> > ...
> 
> Neither of these should cause any problems for the atmel_spi driver
> since it manages chip selects using gpio and sets the MODFDIS bit in MR
> to disable mode fault detection (I actually ran into both erratas myself
> while developing the driver.)

Yet, I got the report (at91rm9200 specific).  Bill?  (I remember
MODFDIS acting oddly, non-rm9200, but forget the details.)  And in
any case there seem to be other folk reporting rm9200 + dataflash
issues ... while mtd_dataflash doesn't seem to be at fault.  So
maybe that combination of errata isn't the issue, but something
else is making the problem. 


> > I've CC'd the relevant folk from Atmel.  Seems that maybe rm9200
> > needs to have a special case whereby chipselect zero is managed
> > by the hardware despite the first erratum.  And maybe that because
> > of that erratum, the DMA chaining needs to be made to work... else
> > root-on-dataflash won't behave.  (Or some other workaround.)
> 
> Hmm...I don't think I understand why DMA chaining will help in this
> case. Could you explain a bit more?

It *might* help -- by keeping the transfer buffer busy enough that
the "auto-deselect" erratum needn't kick in with some basic request
and response protocol operations.

- Dave

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