Re: options USB_FRAG_DMA_WORKAROUND

[Matt Thomas <matt%3am-software.com@localhost>]

On Jan 1, 2011, at 6:52 PM, Jonathan A. Kollasch wrote:

> Hi,
> 
> I noticed the new USB_FRAG_DMA_WORKAROUND option.
> I had previously seen this bug on amd64 during heavy umass(4) use on ehci(4).
> Maybe we should enable this everywhere by default?

I first saw that on my mpc85xx port but I thought it was a local bug.  Then 
Frank reported something similar on ofppc so I committed it to  see if it made 
his problem go away (which it did).  That made me think it is a PowerPC bus_dma 
bug.  But it still confused me since the mpc85xx does not have a cache which is 
coherent in regards to DMA but ofppc does have a DMA coherent cache.

But if you are seeing this on non-PowerPC, I have to wonder if the problem is 
in the USB code itself since amd64 also has a DMA coherent cache.