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| author | Oliver Neukum <oneukum@suse.com> | 2018-09-05 17:56:46 +0200 |
|---|---|---|
| committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2018-09-10 20:40:29 +0200 |
| commit | df3aa13c7bbb307e172c37f193f9a7aa058d4739 (patch) | |
| tree | a06040ae7f90e44fb7603723a81554dde0aeb66d /drivers/usb/class/cdc-acm.h | |
| parent | usb: Change usb_of_get_companion_dev() place to usb/common (diff) | |
| download | linux-df3aa13c7bbb307e172c37f193f9a7aa058d4739.tar.xz linux-df3aa13c7bbb307e172c37f193f9a7aa058d4739.zip | |
Revert "cdc-acm: implement put_char() and flush_chars()"
This reverts commit a81cf9799ad7299b03a4dff020d9685f9ac5f3e0.
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: a81cf9799ad7 ("cdc-acm: implement put_char() and flush_chars()")
Cc: stable <stable@vger.kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Diffstat (limited to 'drivers/usb/class/cdc-acm.h')
| -rw-r--r-- | drivers/usb/class/cdc-acm.h | 1 |
1 files changed, 0 insertions, 1 deletions
diff --git a/drivers/usb/class/cdc-acm.h b/drivers/usb/class/cdc-acm.h index eacc116e83da..ca06b20d7af9 100644 --- a/drivers/usb/class/cdc-acm.h +++ b/drivers/usb/class/cdc-acm.h @@ -96,7 +96,6 @@ struct acm { unsigned long read_urbs_free; struct urb *read_urbs[ACM_NR]; struct acm_rb read_buffers[ACM_NR]; - struct acm_wb *putbuffer; /* for acm_tty_put_char() */ int rx_buflimit; spinlock_t read_lock; u8 *notification_buffer; /* to reassemble fragmented notifications */ |