linux-kernel - [PATCH 1/2] usbip: Skip DMA mapping and unmapping for urb at vhci

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Message-Id: <20190621174553.28862-2-suwan.kim027@gmail.com>
Date:   Sat, 22 Jun 2019 02:45:52 +0900
From:   Suwan Kim <suwan.kim027@...il.com>
To:     shuah@...nel.org, stern@...land.harvard.edu,
        valentina.manea.m@...il.com, gregkh@...uxfoundation.org
Cc:     linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org,
        Suwan Kim <suwan.kim027@...il.com>
Subject: [PATCH 1/2] usbip: Skip DMA mapping and unmapping for urb at vhci

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.

When vhci supports SG, it is useful to use native SG list instead
of mapped SG list because dma mapping fnuction can adjust the
number of SG list that is urb->num_mapped_sgs.

But hcd provides dma mapping and unmapping function by defualt.
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.

Signed-off-by: Suwan Kim <suwan.kim027@...il.com>
---
 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..be87c8a63e24 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.controller, "vhci does not map urb for dma\n");
+	return 0;
+}
+
+static void vhci_unmap_urb_for_dma(struct usb_hcd *hcd, struct urb *urb)
+{
+	dev_dbg(hcd->self.controller, "vhci does not unmap urb 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,
-- 
2.20.1