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* [PATCH v2] usbip: Skip DMA mapping and unmapping for urb at vhci
@ 2019-06-19 15:40 Suwan Kim
  0 siblings, 0 replies; only message in thread
From: Suwan Kim @ 2019-06-19 15:40 UTC (permalink / raw)
  To: shuah, valentina.manea.m, gregkh
  Cc: linux-usb, linux-kernel, stern, Suwan Kim

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 and unmapping function by defualt and
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.

Signed-off-by: Suwan Kim <>
 - Rename the subject of the patch
 - Add unmap_urb_for_dma function according to Alan's comment
 drivers/usb/usbip/vhci_hcd.c | 15 +++++++++++++++
 1 file changed, 15 insertions(+)

diff --git a/drivers/usb/usbip/vhci_hcd.c b/drivers/usb/usbip/vhci_hcd.c
index 667d9c0ec905..e26ce22c1b0f 100644
--- a/drivers/usb/usbip/vhci_hcd.c
+++ b/drivers/usb/usbip/vhci_hcd.c
@@ -1287,6 +1287,18 @@ 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.root_hub->dev, "vhci does not map for dma\n");
+	return 0;
+static void vhci_unmap_urb_for_dma(struct usb_hcd *hcd, struct urb *urb)
+	dev_dbg(&hcd->self.root_hub->dev, "vhci does not unmap for dma\n");
 static const struct hc_driver vhci_hc_driver = {
 	.description	= driver_name,
 	.product_desc	= driver_desc,
@@ -1303,6 +1315,9 @@ static const struct hc_driver vhci_hc_driver = {
 	.get_frame_number = vhci_get_frame_number,
+	.map_urb_for_dma = vhci_map_urb_for_dma,
+	.unmap_urb_for_dma = vhci_unmap_urb_for_dma,
 	.hub_status_data = vhci_hub_status,
 	.hub_control    = vhci_hub_control,
 	.bus_suspend	= vhci_bus_suspend,

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2019-06-19 15:40 [PATCH v2] usbip: Skip DMA mapping and unmapping for urb at vhci Suwan Kim

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