DMA/cache problems on SA1110/SA1111 (Was: Re: USB Host on a SA1111)

[Filip Zyzniewski]

On Thu, Dec 17, 2009 at 10:13 PM, Russell King - ARM Linux
<linux at arm.linux.org.uk> wrote:

>> Russell you got any clues on this? From my point of view it really should
>> just work. But Ive never done this myself.
>
> I've never really been that much involved with USB stuff, so can't really
> comment.
>

There was some discussion about this at linux-usb mailing list.
The interesting part is here:
http://thread.gmane.org/gmane.linux.usb.general/25732

Especially the last post by Alan Stern:

> I looked at one of these logs.  Apparently there's a problem with the
> memory caching and DMA.  With some of the commands, the debugging
> message shows incorrect data in the buffer.  But later on, when the
> data gets used, it obviously is correct.
> This implies that something is wrong with the implementation of
> dma_map_single() or dma_unmap_unsingle().  And it might explain why
> changing the system's cache settings affects the behavior.

I don't know architecture handling details, could somebody more
knowledgeable give me
some clues about where to begin fixing this? What could be broken?

regards,
Filip Zyzniewski