This is a note to let you know that I've just added the patch titled
usb: cdns3: fix NCM gadget RX speed 20x slow than expection at iMX8QM
to the 5.10-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
usb-cdns3-fix-ncm-gadget-rx-speed-20x-slow-than-expe.patch
and it can be found in the queue-5.10 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
commit cafa7e0b517f7e15e1060be521f38736424777f7
Author: Frank Li <Frank.Li@xxxxxxx>
Date: Thu May 18 11:49:45 2023 -0400
usb: cdns3: fix NCM gadget RX speed 20x slow than expection at iMX8QM
[ Upstream commit dbe678f6192f27879ac9ff6bc7a1036aad85aae9 ]
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@xxxxxxxxxxxxxxx
Fixes: 7733f6c32e36 ("usb: cdns3: Add Cadence USB3 DRD Driver")
Signed-off-by: Frank Li <Frank.Li@xxxxxxx>
Link: https://lore.kernel.org/r/20230518154946.3666662-1-Frank.Li@xxxxxxx
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
diff --git a/drivers/usb/cdns3/gadget.c b/drivers/usb/cdns3/gadget.c
index 24dab7006b823..210c1d6150825 100644
--- a/drivers/usb/cdns3/gadget.c
+++ b/drivers/usb/cdns3/gadget.c
@@ -2098,6 +2098,19 @@ int cdns3_ep_config(struct cdns3_endpoint *priv_ep, bool enable)
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;
+
mult = min_t(u8, mult, EP_CFG_MULT_MAX);
buffering = min_t(u8, buffering, EP_CFG_BUFFERING_MAX);
maxburst = min_t(u8, maxburst, EP_CFG_MAXBURST_MAX);
