ixp4xx dmabounce

[Brian Walsh]

On Thu, Sep 17, 2009 at 5:53 PM, Russell King - ARM Linux
<linux at arm.linux.org.uk> wrote:
>
> On Thu, Sep 17, 2009 at 05:02:59PM -0400, Brian Walsh wrote:
> > Any ideas or suggestions?
>
> It's caused because we don't allow dma_free_coherent() to be called from
> IRQ context (which is reasonable because it needs to flush TLBs across
> all processors on SMP systems.)
>

I am not running on an SMP system so would this even be a problem?

>
> Unfortunately, with the DMA bounce code enabled, this function does get
> called from IRQ context, and so tends to spit out these warnings.
>
> I did have a patch which made dma_free_coherent() lazy, but it was
> reported that the suffered disk corruption (though it was never
> conclusive whether it was caused by the patch or not.)  Here's an
> updated version of that patch.
>

I did not see any data rate improvement using this patch over just commenting
out the warning stack dump.  I am still seeing about half the data transfer rate
using the high speed ehci USB controller over the full speed ohci USB
controller.