Re: [PATCH v3 1/2] usbip: Skip DMA mapping and unmapping for urb at vhci

[shuah]

On 8/4/19 11:23 PM, Suwan Kim wrote:
> On Fri, Aug 02, 2019 at 04:22:27PM -0600, shuah wrote:
> > On 8/2/19 11:36 AM, Suwan Kim wrote:
> > > vhci doesnât do DMA for remote device. Actually, the real DMA
> > > operation is done by network card driver. vhci just passes virtual
> > > address of the buffer to the network stack, so vhci doesnât use and
> > > need dma address of the buffer of the URB.
> > >
> > > But HCD provides DMA mapping and unmapping function by default.
> > > Moreover, it causes unnecessary DMA mapping and unmapping which
> > > will be done again at the NIC driver and it wastes CPU cycles.
> > > So, implement map_urb_for_dma and unmap_urb_for_dma function for
> > > vhci in order to skip the DMA mapping and unmapping procedure.
> > >
> > > When it comes to supporting SG for vhci, it is useful to use native
> > > SG list (urb->num_sgs) instead of mapped SG list because DMA mapping
> > > fnuction can adjust the number of SG list (urb->num_mapped_sgs).
> > > And vhci_map_urb_for_dma() prevents isoc pipe from using SG as
> > > hcd_map_urb_for_dma() does.
> > >
> > > Signed-off-by: Suwan Kim <suwan.kim027@xxxxxxxxx>
> > > ---
> > >    drivers/usb/usbip/vhci_hcd.c | 19 +++++++++++++++++++
> > >    1 file changed, 19 insertions(+)
> > >
> > > diff --git a/drivers/usb/usbip/vhci_hcd.c b/drivers/usb/usbip/vhci_hcd.c
> > > index 000ab7225717..c62f7fa8118c 100644
> > > --- a/drivers/usb/usbip/vhci_hcd.c
> > > +++ b/drivers/usb/usbip/vhci_hcd.c
> > > @@ -1288,6 +1288,22 @@ 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)
> > > +{
> > > +	if (usb_endpoint_xfer_isoc(&urb->ep->desc) && urb->num_sgs) {
> > > +		WARN_ON(1);
> >
> > Don't add WARN_ON. I cleaned them all up recently and don't want new
> > ones added.
>
> Ok. I will remove it and resend v4.

Please add appropriate error message in place of WARN_ON

thanks,
-- Shuah