USB mass storage and ARM cache coherency

[Shilimkar, Santosh]

> -----Original Message-----
> From: Oliver Neukum [mailto:oliver at neukum.org]
> Sent: Wednesday, February 17, 2010 2:41 PM
> To: Shilimkar, Santosh
> Cc: Russell King - ARM Linux; Catalin Marinas; Pavel Machek; Greg KH; Matthew Dharm; Sergei Shtylyov;
> Ming Lei; Sebastian Siewior; linux-usb at vger.kernel.org; linux-kernel; linux-arm-kernel; Mankad,
> Maulik Ojas; Gadiyar, Anand
> Subject: Re: USB mass storage and ARM cache coherency
> 
> Am Mittwoch, 17. Februar 2010 09:55:08 schrieb Shilimkar, Santosh:
> > > Your original patch however kills ehci, ohci and uhci on some architectures.
> >
> > How about below approach? Controller driver can set
> > "uses_pio_for_control" if it can't do dma for control transfer.
> >
> > diff --git a/drivers/usb/core/hcd.c b/drivers/usb/core/hcd.c
> > index 80995ef..e3eae02 100644
> > --- a/drivers/usb/core/hcd.c
> > +++ b/drivers/usb/core/hcd.c
> > @@ -1276,7 +1276,7 @@ static int map_urb_for_dma(struct usb_hcd *hcd, struct urb *urb,
> >
> >         if (usb_endpoint_xfer_control(&urb->ep->desc)
> >             && !(urb->transfer_flags & URB_NO_SETUP_DMA_MAP)) {
> > -               if (hcd->self.uses_dma) {
> > +               if (hcd->self.uses_dma && !hcd->self.uses_pio_for_control) {
> 
> It is not elegant to describe exceptions. It would be better, if you split up
> the flag into two flags, called uses_dma_for_ordinary_transfers and
> uses_dma_for control_transfers. Doing so also makes sure you look at
> all hcd drivers ;-)
> 
Good point. Negative checks are any way not elegant
> And the tests become straightforward. And please add a detailed comment
> to explain why this differentiation is needed on ARM.
OK. I shall create a patch with description about the problem.

Thanks for feedback!!

Regards,
Santosh