linux-kernel - [PATCH 1/2] usb: cdns3: improve handling of unaligned address case

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Message-Id: <20230518204947.3770236-1-Frank.Li@nxp.com>
Date:   Thu, 18 May 2023 16:49:45 -0400
From:   Frank Li <Frank.Li@....com>
To:     Peter Chen <peter.chen@...nel.org>,
        Pawel Laszczak <pawell@...ence.com>,
        Roger Quadros <rogerq@...nel.org>,
        Aswath Govindraju <a-govindraju@...com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-usb@...r.kernel.org (open list:CADENCE USB3 DRD IP DRIVER),
        linux-kernel@...r.kernel.org (open list)
Cc:     imx@...ts.linux.dev
Subject: [PATCH 1/2] usb: cdns3: improve handling of unaligned address case

When the address of a request was not aligned with an 8-byte boundary, the
USB DMA was unable to process it, necessitating the use of an internal
bounce buffer.

In these cases, the request->buf had to be copied to/from this bounce
buffer. However, if this unaligned address scenario arises, it is
unnecessary to perform heavy cache maintenance operations like
usb_gadget_map(unmap)_request_by_dev() on the request->buf, as the DMA
does not utilize it at all. it can be skipped at this case.

iperf3 tests on the rndis case:

Transmit speed (TX): Improved from 299Mbps to 440Mbps
Receive speed (RX): Improved from 290Mbps to 500Mbps

Signed-off-by: Frank Li <Frank.Li@....com>
---
 drivers/usb/cdns3/cdns3-gadget.c | 11 +++++++----
 1 file changed, 7 insertions(+), 4 deletions(-)

diff --git a/drivers/usb/cdns3/cdns3-gadget.c b/drivers/usb/cdns3/cdns3-gadget.c
index 1dcadef933e3..09a0882a4e97 100644
--- a/drivers/usb/cdns3/cdns3-gadget.c
+++ b/drivers/usb/cdns3/cdns3-gadget.c
@@ -800,7 +800,8 @@ void cdns3_gadget_giveback(struct cdns3_endpoint *priv_ep,
 	if (request->status == -EINPROGRESS)
 		request->status = status;
 
-	usb_gadget_unmap_request_by_dev(priv_dev->sysdev, request,
+	if (likely(!(priv_req->flags & REQUEST_UNALIGNED)))
+		usb_gadget_unmap_request_by_dev(priv_dev->sysdev, request,
 					priv_ep->dir);
 
 	if ((priv_req->flags & REQUEST_UNALIGNED) &&
@@ -2543,10 +2544,12 @@ static int __cdns3_gadget_ep_queue(struct usb_ep *ep,
 	if (ret < 0)
 		return ret;
 
-	ret = usb_gadget_map_request_by_dev(priv_dev->sysdev, request,
+	if (likely(!(priv_req->flags & REQUEST_UNALIGNED))) {
+		ret = usb_gadget_map_request_by_dev(priv_dev->sysdev, request,
 					    usb_endpoint_dir_in(ep->desc));
-	if (ret)
-		return ret;
+		if (ret)
+			return ret;
+	}
 
 	list_add_tail(&request->list, &priv_ep->deferred_req_list);
 
-- 
2.34.1