RE: USB mass storage and ARM cache coherency

[Alan Stern]

On Tue, 16 Feb 2010, Shilimkar, Santosh wrote:

> > Your original patch however kills ehci, ohci and uhci on some architectures.
> Well the patch was making _ONLY_ control transfers use PIO and rest of
> the transfer would still use dma. So not sure how much performance impact would
> be because of that.
> Another issue with that patch is there are few controllers which can't do PIO
> at all and hence the patch would broke those controllers.

More than "a few"!  None of the EHCI, OHCI, or UHCI controllers used in
Intel-compatible desktop and laptop systems can do PIO.  That's what 
Oliver meant.

Alan Stern

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