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SubjectRe: [PATCH] usbip: Implement map_urb_for_dma function for vhci to skip dma mapping
On Tue, Jun 18, 2019 at 11:30:34AM -0400, Alan Stern wrote:
> On Tue, 18 Jun 2019, Suwan Kim wrote:
>
> > vhci doesn’t do dma for remote device. Actually, the real dma
> > operation is done by network card driver. So, vhci doesn’t use and
> > need dma address of transfer buffer of urb.
> >
> > But hcd provides dma mapping function by defualt in usb_hcd_submit_urb()
> > and it causes unnecessary dma mapping which will be done again at
> > NIC driver and it wastes CPU cycles. So, implement map_urb_for_dma
> > function for vhci in order to skip the dma mapping procedure.
> >
> > Signed-off-by: Suwan Kim <suwan.kim027@gmail.com>
> > ---
> > drivers/usb/usbip/vhci_hcd.c | 8 ++++++++
> > 1 file changed, 8 insertions(+)
> >
> > diff --git a/drivers/usb/usbip/vhci_hcd.c b/drivers/usb/usbip/vhci_hcd.c
> > index 667d9c0ec905..9df4d9e36788 100644
> > --- a/drivers/usb/usbip/vhci_hcd.c
> > +++ b/drivers/usb/usbip/vhci_hcd.c
> > @@ -1287,6 +1287,13 @@ static int vhci_free_streams(struct usb_hcd *hcd, struct usb_device *udev,
> > return 0;
> > }
> >
> > +static int vhci_map_urb_for_dma(struct usb_hcd *hcd, struct urb *urb,
> > + gfp_t mem_flags)
> > +{
> > + dev_dbg(hcd->self.controller, "vhci does not map urb for dma\n");
> > + return 0;
> > +}
> > +
> > static const struct hc_driver vhci_hc_driver = {
> > .description = driver_name,
> > .product_desc = driver_desc,
> > @@ -1302,6 +1309,7 @@ static const struct hc_driver vhci_hc_driver = {
> > .urb_dequeue = vhci_urb_dequeue,
> >
> > .get_frame_number = vhci_get_frame_number,
> > + .map_urb_for_dma = vhci_map_urb_for_dma,
> >
> > .hub_status_data = vhci_hub_status,
> > .hub_control = vhci_hub_control,
>
> If the goal is to avoid wasting CPU cycles, you probably should have a
> vhci_unmap_urb_for_dma routine as well.

I missed that. Thank you for pointing it out.
I will send v2 including unmap function.

Regards

Suwan Kim

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