Linux: AM335x Quad-USB-to-UART Bridge (CP2108) Communcation Freeze

2818.config.gz

Hi Bin,

The flowing is my test steps on non-RT kernel. 

root@NECRO:~# ls /dev/ttyUSB*

/dev/ttyUSB0  /dev/ttyUSB1  /dev/ttyUSB2  /dev/ttyUSB3

root@NECRO:~# cat /proc/version

Linux version 4.14.79-ge669d52447 (fan@ubuntu) (gcc version 7.2.1 20171011 (Linaro GCC 7.2-2017.11)) #6 PREEMPT Mon Apr 15 18:04:56 PDT 2019

root@NECRO:~# cat /dev/ttyUSB1 &

[1] 717

root@NECRO:~# kill $(pidof cat)

root@NECRO:~# cat /dev/ttyUSB2 &

[2] 721

[1]   Terminated              cat /dev/ttyUSB1

root@NECRO:~# kill $(pidof cat)

root@NECRO:~# cat /dev/ttyUSB3 &

[3] 724

[2]   Terminated              cat /dev/ttyUSB2

root@NECRO:~# kill $(pidof cat)

root@NECRO:~# cat /dev/ttyUSB1 &

[1] 728

root@NECRO:~# kill $(pidof cat)

root@NECRO:~# cat /dev/ttyUSB0 &

[2] 733

[1]   Terminated              cat /dev/ttyUSB1

root@NECRO:~# kill $(pidof cat)

root@NECRO:~# cat /dev/ttyUSB3 &

[3] 737

root@NECRO:~# [  233.600688] cp210x ttyUSB0: failed set request 0x12 status: -110

[  237.760719] cp210x ttyUSB3: failed set request 0x0 status: -110

[  237.766724] cp210x ttyUSB3: cp210x_open - Unable to enable UART

cat: can't open '/dev/ttyUSB3': Input/output error

[  238.640691] cp210x ttyUSB0: failed set request 0x0 status: -110

This error on my custom board, I have no TI AM335x EVM board.

Thanks

Shuming

We had a similar issue a work around i found was to unload and reload musb_dsps and musb_hdrc, this might help you out for the time being

These modules should be under "/lib/modules/$(uname -r)/kernel/drivers/usb/musb"

unload:
rmmod musb_dsps
rmmod musb_hdrc

reload:
insmod musb_hdrc.ko
insmod musb_dsps.ko

This is just a workaround though.

Hi Ben,

I tested the same kernel with your .config, but was unable to see the problem.

Here is the test script I used, ran for almost 30min until now.

#!/bin/sh
while true; do
        for i in 0 1 2 3; do
                cat /dev/ttyUSB${i} || exit 1 &
                sleep 1
                kill $(pidof cat) || exit 2
                sleep 1
        done
done

By the way, attached below is a kernel patch fixing a cppi driver bug. I don't think it is related, but can you please give it a try?

From 01a3e84503d595623be207943e01b34028320025 Mon Sep 17 00:00:00 2001
From: Bin Liu <b-liu@ti.com>
Date: Fri, 9 Nov 2018 14:54:06 -0600
Subject: [PATCH] dma: cppi41: delete channel from pending list when stop
 channel

The driver defines three states for a cppi channel.
- idle: .chan_busy == 0 && not in .pending list
- pending: .chan_busy == 0 && in .pending list
- busy: .chan_busy == 1 && not in .pending list

There are cases in which the cppi channel could be in the pending state
when cppi41_dma_issue_pending() is called after cppi41_runtime_suspend()
is called.

cppi41_stop_chan() has a bug for these cases to set channels to idle state.
It only checks the .chan_busy flag, but not the .pending list, then later
when cppi41_runtime_resume() is called the channels in .pending list will
be transitioned to busy state.

Removing channels from the .pending list solves the problem.

Fixes: 975faaeb9985 ("dma: cppi41: start tear down only if channel is busy")
Cc: stable@vger.kernel.org # v3.15+
Signed-off-by: Bin Liu <b-liu@ti.com>
---
 drivers/dma/ti/cppi41.c | 16 +++++++++++++++-
 1 file changed, 15 insertions(+), 1 deletion(-)

diff --git a/drivers/dma/ti/cppi41.c b/drivers/dma/ti/cppi41.c
index beab6d1dea93..f28be46bd3a2 100644
--- a/drivers/dma/ti/cppi41.c
+++ b/drivers/dma/ti/cppi41.c
@@ -723,8 +723,22 @@ static int cppi41_stop_chan(struct dma_chan *chan)
 
 	desc_phys = lower_32_bits(c->desc_phys);
 	desc_num = (desc_phys - cdd->descs_phys) / sizeof(struct cppi41_desc);
-	if (!cdd->chan_busy[desc_num])
+	if (!cdd->chan_busy[desc_num]) {
+		struct cppi41_channel *cc, *_ct;
+
+		/*
+		 * channels might still be in the pendling list if
+		 * cppi41_dma_issue_pending() is called after
+		 * cppi41_runtime_suspend() is called
+		 */
+		list_for_each_entry_safe(cc, _ct, &cdd->pending, node) {
+			if (cc != c)
+				continue;
+			list_del(&cc->node);
+			break;
+		}
 		return 0;
+	}
 
 	ret = cppi41_tear_down_chan(c);
 	if (ret)
-- 
2.17.1