CPU Cache and busdma usage in USB

Rafal Jaworowski raj at semihalf.com
Wed Jul 8 09:14:27 UTC 2009

On 2009-07-07, at 18:46, Hans Petter Selasky wrote:

>> I had Checked USB behaviour on PowerPC without hardware cache  
>> coherency.
>> The problem also exists here and patch helps.
> In my source code view the busdma sync function is empty for power- 
> pc. Your
> patch should have no effect at all for sync operations?

This was about the PPC4xx PowerPC port, not committed to the tree yet.  
Unlike most PowerPC this system has a de-coherent DMA and therefore  
its busdma sync is non empty, but needs to enforce coherency by  

The point is this is another platform on which USB stack (usb_pc_cpu_*  
functions) shows similar issues as reported for ARM and MIPS.


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