From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-6.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 43391C31E5B for ; Tue, 18 Jun 2019 15:30:39 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 1C0D72085A for ; Tue, 18 Jun 2019 15:30:39 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729554AbfFRPaf (ORCPT ); Tue, 18 Jun 2019 11:30:35 -0400 Received: from iolanthe.rowland.org ([192.131.102.54]:40202 "HELO iolanthe.rowland.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with SMTP id S1729320AbfFRPaf (ORCPT ); Tue, 18 Jun 2019 11:30:35 -0400 Received: (qmail 5734 invoked by uid 2102); 18 Jun 2019 11:30:34 -0400 Received: from localhost (sendmail-bs@127.0.0.1) by localhost with SMTP; 18 Jun 2019 11:30:34 -0400 Date: Tue, 18 Jun 2019 11:30:34 -0400 (EDT) From: Alan Stern X-X-Sender: stern@iolanthe.rowland.org To: Suwan Kim cc: shuah@kernel.org, , , , Subject: Re: [PATCH] usbip: Implement map_urb_for_dma function for vhci to skip dma mapping In-Reply-To: <20190618142817.16844-1-suwan.kim027@gmail.com> Message-ID: MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=UTF-8 Content-Transfer-Encoding: 8BIT Sender: linux-usb-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-usb@vger.kernel.org On Tue, 18 Jun 2019, Suwan Kim wrote: > 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 function by defualt in usb_hcd_submit_urb() > and it causes unnecessary dma mapping which will be done again at > NIC driver and it wastes CPU cycles. So, implement map_urb_for_dma > function for vhci in order to skip the dma mapping procedure. > > Signed-off-by: Suwan Kim > --- > drivers/usb/usbip/vhci_hcd.c | 8 ++++++++ > 1 file changed, 8 insertions(+) > > diff --git a/drivers/usb/usbip/vhci_hcd.c b/drivers/usb/usbip/vhci_hcd.c > index 667d9c0ec905..9df4d9e36788 100644 > --- a/drivers/usb/usbip/vhci_hcd.c > +++ b/drivers/usb/usbip/vhci_hcd.c > @@ -1287,6 +1287,13 @@ 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 const struct hc_driver vhci_hc_driver = { > .description = driver_name, > .product_desc = driver_desc, > @@ -1302,6 +1309,7 @@ static const struct hc_driver vhci_hc_driver = { > .urb_dequeue = vhci_urb_dequeue, > > .get_frame_number = vhci_get_frame_number, > + .map_urb_for_dma = vhci_map_urb_for_dma, > > .hub_status_data = vhci_hub_status, > .hub_control = vhci_hub_control, If the goal is to avoid wasting CPU cycles, you probably should have a vhci_unmap_urb_for_dma routine as well. Alan Stern