Re: [PATCH v5 1/2] usbip: Skip DMA mapping and unmapping for urb at vhci

[shuah]

On 8/8/19 10:18 AM, shuah wrote:
> On 8/8/19 9:54 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>
> > ---
> > v4 - v5
> > - Replace pr_err() with dev_err() in the error path.
> >
> > v3 - v4
> > - Replace WARN_ON() with pr_err() in the error path.
> >
> > v2 - v3
> > - Move setting URB_DMA_MAP_SG flag to the patch 2.
> > - Prevent isoc pipe from using SG buffer.
> >
> > v1 - v2
> > - Add setting URB_DMA_MAP_SG flag in urb->transfer_flags to tell
> > stub driver to use SG buffer.
> > ---
> > Â drivers/usb/usbip/vhci_hcd.c | 19 +++++++++++++++++++
> > Â 1 file changed, 19 insertions(+)
> >
> > diff --git a/drivers/usb/usbip/vhci_hcd.c b/drivers/usb/usbip/vhci_hcd.c
> > index 000ab7225717..ea82b932a2f9 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,
> > ÂÂÂÂÂ return 0;
> > Â }
> > +static int vhci_map_urb_for_dma(struct usb_hcd *hcd, struct urb *urb,
> > +ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ gfp_t mem_flags)
> > +{
> > +ÂÂÂ if (usb_endpoint_xfer_isoc(&urb->ep->desc) && urb->num_sgs) {
> > +ÂÂÂÂÂÂÂ dev_err(&urb->dev->dev, "SG is not supported for isochronous 
> > transfer\n");
> > +ÂÂÂÂÂÂÂ return -EINVAL;
> > +ÂÂÂ }
> > +
> > +ÂÂÂ return 0;
> > +}
> > +
> > +static void vhci_unmap_urb_for_dma(struct usb_hcd *hcd, struct urb *urb)
> > +{
> > +ÂÂÂ dev_dbg(hcd->self.controller, "vhci does not unmap urb for dma\n");
> > +}
> > +
> > Â static const struct hc_driver vhci_hc_driver = {
> > ÂÂÂÂÂ .descriptionÂÂÂ = driver_name,
> > ÂÂÂÂÂ .product_descÂÂÂ = driver_desc,
> > @@ -1304,6 +1320,9 @@ static const struct hc_driver vhci_hc_driver = {
> > ÂÂÂÂÂ .get_frame_number = vhci_get_frame_number,
> > +ÂÂÂ .map_urb_for_dma = vhci_map_urb_for_dma,
> > +ÂÂÂ .unmap_urb_for_dma = vhci_unmap_urb_for_dma,
> > +
> > ÂÂÂÂÂ .hub_status_data = vhci_hub_status,
> > ÂÂÂÂÂ .hub_controlÂÂÂ = vhci_hub_control,
> > ÂÂÂÂÂ .bus_suspendÂÂÂ = vhci_bus_suspend,
>
> Looks good to me.
>
> Reviewed-by: Shuah Khan <skhan@xxxxxxxxxxxxxxxxxxx>

Greg!

Please pick this one up.

Acked-by: Shuah Khan <skhan@xxxxxxxxxxxxxxxxxxx>

thanks,
-- Shuah