Messages in this thread | | | Subject | Re: [PATCH v4 1/2] usbip: Skip DMA mapping and unmapping for urb at vhci | From | shuah <> | Date | Tue, 6 Aug 2019 09:11:30 -0600 |
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On 8/6/19 6:31 AM, Suwan Kim wrote: > vhci doesn’t 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 doesn’t 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@gmail.com> > --- > 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. > --- > 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..429e4e989f38 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) { > + pr_err("SG is not supported for isochronous transfer\n");
Any reason to not use dev_err()?
Looks good otherwise.
thanks, -- Shuah
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