USB mass storage and ARM cache coherency

Benjamin Herrenschmidt benh at
Thu Feb 25 15:52:58 EST 2010

On Wed, 2010-02-24 at 16:50 -0500, Alan Stern wrote:
> The main issue here is that the same host controller will use PIO
> sometimes and DMA sometimes, depending on the details of the
> transfer.  
> The USB core didn't expect this and consequently we violated the rules
> for DMA mapping.  The question is: If the core is fixed so that the
> rules aren't violated, will everything work correctly? 

As long as the only issue is that one (ie, doing PIO while dma-map'ed),
then yes, I'd say things should work. If not, then there is -another-
problem to be fixed :-)


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