linux/drivers/usb/class
Oliver Neukum df3aa13c7b Revert "cdc-acm: implement put_char() and flush_chars()"
This reverts commit a81cf9799a.

The patch causes a regression, which I cannot find the reason for.
So let's revert for now, as a revert hurts only performance.

Original report:
I was trying to resolve the problem with Oliver but we don't get any conclusion
for 5 months, so I am now sending this to mail list and cdc_acm authors.

I am using simple request-response protocol to obtain the boiller parameters
in constant intervals.

A simple one transaction is:
1. opening the /dev/ttyACM0
2. sending the following 10-bytes request to the device:
   unsigned char req[] = {0x02, 0xfe, 0x01, 0x05, 0x08, 0x02, 0x01, 0x69, 0xab, 0x03};
3. reading response (frame of 74 bytes length).
4. closing the descriptor
I am doing this transaction with 5 seconds intervals.

Before the bad commit everything was working correctly: I've got a requests and
a responses in a timely manner.

After the bad commit more time I am using the kernel module, more problems I have.
The graph [2] is showing the problem.

As you can see after module load all seems fine but after about 30 minutes I've got
a plenty of EAGAINs when doing read()'s and trying to read back the data.

When I rmmod and insmod the cdc_acm module again, then the situation is starting
over again: running ok shortly after load, and more time it is running, more EAGAINs
I have when calling read().

As a bonus I can see the problem on the device itself:
The device is configured as you can see here on this screen [3].
It has two transmision LEDs: TX and RX. Blink duration is set for 100ms.
This is a recording before the bad commit when all is working fine: [4]
And this is with the bad commit: [5]
As you can see the TX led is blinking wrongly long (indicating transmission?)
and I have problems doing read() calls (EAGAIN).

Reported-by: Mariusz Bialonczyk <manio@skyboo.net>
Signed-off-by: Oliver Neukum <oneukum@suse.com>
Fixes: a81cf9799a ("cdc-acm: implement put_char() and flush_chars()")
Cc: stable <stable@vger.kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
2018-09-10 20:40:29 +02:00
..
cdc-acm.c Revert "cdc-acm: implement put_char() and flush_chars()" 2018-09-10 20:40:29 +02:00
cdc-acm.h Revert "cdc-acm: implement put_char() and flush_chars()" 2018-09-10 20:40:29 +02:00
cdc-wdm.c usb: cdc-wdm: Fix a sleep-in-atomic-context bug in service_outstanding_interrupt() 2018-09-05 14:48:40 +02:00
Kconfig usb: fix some references for /proc/bus/usb 2017-04-18 16:54:19 +02:00
Makefile USB: add SPDX identifiers to all remaining Makefiles 2017-11-07 15:53:48 +01:00
usblp.c usb: usblp: use irqsave() in USB's complete callback 2018-06-28 19:36:06 +09:00
usbtmc.c usb: usbtmc: Add support for 32 bit compat applications 2018-07-24 13:50:50 +02:00