Re: USB mass storage and ARM cache coherency

[Oliver Neukum <oliver@neukum.org>]

Am Dienstag, 16. Februar 2010 15:12:45 schrieb Shilimkar, Santosh:
> > > > I am afraid for these controllers the controller driver must be responsible
> > > > for all DMA and cache issues. Indicating the exact requirements to the
> > > > upper layer would be a battle already lost.
> > > > so the safe choice is not to set has_dma and the generic layer will leave
> > > > the issue to the lower level.
> > > This means don't use dma at all which will almost kill the performance.
> > 
> > Why would you be unable to map a buffer in the hcd driver when you know
> > that you'll use DMA?
> Probably it can be. The USB stack has the dma maintenance code at common 
> place for all controllers and hence we were just trying to see if there is 
> way to handle that way.

This is true. If you can find a clean way to describe your requirements
to the generic layer, that would be better. The problem is that we must
not end up with a dozen flags.

Your original patch however kills ehci, ohci and uhci on some architectures.

	Regards
		Oliver