linux-kernel - [PATCH 4.9 051/139] usb: gadget: u_ether: enable qmult on SuperSpeed Plus as well

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Date:   Tue, 27 Oct 2020 14:49:05 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org,
        Maciej Żenczykowski <maze@...gle.com>,
        Lorenzo Colitti <lorenzo@...gle.com>,
        Felipe Balbi <balbi@...nel.org>,
        Sasha Levin <sashal@...nel.org>
Subject: [PATCH 4.9 051/139] usb: gadget: u_ether: enable qmult on SuperSpeed Plus as well

From: Lorenzo Colitti <lorenzo@...gle.com>

[ Upstream commit 4eea21dc67b0c6ba15ae41b1defa113a680a858e ]

The u_ether driver has a qmult setting that multiplies the
transmit queue length (which by default is 2).

The intent is that it should be enabled at high/super speed, but
because the code does not explicitly check for USB_SUPER_PLUS,
it is disabled at that speed.

Fix this by ensuring that the queue multiplier is enabled for any
wired link at high speed or above. Using >= for USB_SPEED_*
constants seems correct because it is what the gadget_is_xxxspeed
functions do.

The queue multiplier substantially helps performance at higher
speeds. On a direct SuperSpeed Plus link to a Linux laptop,
iperf3 single TCP stream:

Before (qmult=1): 1.3 Gbps
After  (qmult=5): 3.2 Gbps

Fixes: 04617db7aa68 ("usb: gadget: add SS descriptors to Ethernet gadget")
Reviewed-by: Maciej Żenczykowski <maze@...gle.com>
Signed-off-by: Lorenzo Colitti <lorenzo@...gle.com>
Signed-off-by: Felipe Balbi <balbi@...nel.org>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 drivers/usb/gadget/function/u_ether.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/usb/gadget/function/u_ether.c b/drivers/usb/gadget/function/u_ether.c
index d5fbc2352029b..589d1f5fb575a 100644
--- a/drivers/usb/gadget/function/u_ether.c
+++ b/drivers/usb/gadget/function/u_ether.c
@@ -97,7 +97,7 @@ struct eth_dev {
 static inline int qlen(struct usb_gadget *gadget, unsigned qmult)
 {
 	if (gadget_is_dualspeed(gadget) && (gadget->speed == USB_SPEED_HIGH ||
-					    gadget->speed == USB_SPEED_SUPER))
+					    gadget->speed >= USB_SPEED_SUPER))
 		return qmult * DEFAULT_QLEN;
 	else
 		return DEFAULT_QLEN;
-- 
2.25.1