RE: USB mass storage and ARM cache coherency

[Gadiyar, Anand]

Alan Stern wrote:
> On Wed, 17 Feb 2010, Shilimkar, Santosh wrote:
> 
> > 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) {
> >                       urb->setup_dma = dma_map_single(
> >                                       hcd->self.controller,
> >                                       urb->setup_packet,
> > @@ -1335,7 +1335,7 @@ static void unmap_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)
> >                       dma_unmap_single(hcd->self.controller, urb->setup_dma,
> >                                       sizeof(struct usb_ctrlrequest),
> >                                       DMA_TO_DEVICE);
> > diff --git a/include/linux/usb.h b/include/linux/usb.h
> > index d7ace1b..ba5b0a2 100644
> > --- a/include/linux/usb.h
> > +++ b/include/linux/usb.h
> > @@ -329,6 +329,9 @@ struct usb_bus {
> >       int busnum;                     /* Bus number (in order of reg) */
> >       const char *bus_name;           /* stable id (PCI slot_name etc) */
> >       u8 uses_dma;                    /* Does the host controller use DMA? */
> > +     u8 uses_pio_for_control;        /* Does the host controller use PIO
> > +                                      * for control tansfers?
> > +                                      */
> >       u8 otg_port;                    /* 0, or number of OTG/HNP port */
> >       unsigned is_b_host:1;           /* true during some HNP roleswitches */
> >       unsigned b_hnp_enable:1;        /* OTG: did A-Host enable HNP? */
> 
> Why do you skip mapping the setup packet but not the data packet?
> 

I think that's oversight. For this controller, we need to skip mapping
all buffers used to do transfers on EP0, which is all control transfers.

Will fix in the next version of the patch.

- Anand
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