From dbe678f6192f27879ac9ff6bc7a1036aad85aae9 Mon Sep 17 00:00:00 2001
From: Frank Li <Frank.Li@nxp.com>
Date: Thu, 18 May 2023 11:49:45 -0400
Subject: [PATCH] usb: cdns3: fix NCM gadget RX speed 20x slow than expection
at iMX8QM
Git-commit: dbe678f6192f27879ac9ff6bc7a1036aad85aae9
References: git-fixes
Patch-mainline: v6.4-rc5
At iMX8QM platform, enable NCM gadget and run 'iperf3 -s'.
At host, run 'iperf3 -V -c fe80::6863:98ff:feef:3e0%enxc6e147509498'
[ 5] 0.00-1.00 sec 1.55 MBytes 13.0 Mbits/sec 90 4.18 KBytes
[ 5] 1.00-2.00 sec 1.44 MBytes 12.0 Mbits/sec 75 4.18 KBytes
[ 5] 2.00-3.00 sec 1.48 MBytes 12.4 Mbits/sec 75 4.18 KBytes
Expected speed should be bigger than 300Mbits/sec.
The root cause of this performance drop was found to be data corruption
happening at 4K borders in some Ethernet packets, leading to TCP
checksum errors. This corruption occurs from the position
(4K - (address & 0x7F)) to 4K. The u_ether function's allocation of
skb_buff reserves 64B, meaning all RX addresses resemble 0xXXXX0040.
Force trb_burst_size to 16 can fix this problem.
Cc: stable@vger.kernel.org
Fixes: 7733f6c32e36 ("usb: cdns3: Add Cadence USB3 DRD Driver")
Signed-off-by: Frank Li <Frank.Li@nxp.com>
Link: https://lore.kernel.org/r/20230518154946.3666662-1-Frank.Li@nxp.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Oliver Neukum <oneukum@suse.com>
---
drivers/usb/cdns3/cdns3-gadget.c | 13 +++++++++++++
1 file changed, 13 insertions(+)
--- a/drivers/usb/cdns3/cdns3-gadget.c
+++ b/drivers/usb/cdns3/cdns3-gadget.c
@@ -2097,6 +2097,19 @@ int cdns3_ep_config(struct cdns3_endpoin
else
priv_ep->trb_burst_size = 16;
+ /*
+ * In versions preceding DEV_VER_V2, for example, iMX8QM, there exit the bugs
+ * in the DMA. These bugs occur when the trb_burst_size exceeds 16 and the
+ * address is not aligned to 128 Bytes (which is a product of the 64-bit AXI
+ * and AXI maximum burst length of 16 or 0xF+1, dma_axi_ctrl0[3:0]). This
+ * results in data corruption when it crosses the 4K border. The corruption
+ * specifically occurs from the position (4K - (address & 0x7F)) to 4K.
+ *
+ * So force trb_burst_size to 16 at such platform.
+ */
+ if (priv_dev->dev_ver < DEV_VER_V2)
+ priv_ep->trb_burst_size = 16;
+
/* onchip buffer is only allocated before configuration */
if (!priv_dev->hw_configured_flag) {
ret = cdns3_ep_onchip_buffer_reserve(priv_dev, buffering + 1,