Hi greg
On 2022/4/22 13:07, Greg KH wrote:
On Fri, Apr 22, 2022 at 10:35:59AM +0800, Hongyu Xie wrote:
Hi greg,
On 2022/4/22 00:45, Greg KH wrote:
On Tue, Apr 19, 2022 at 02:54:08PM +0800, Hongyu Xie wrote:
From: Hongyu Xie <xiehongyu1@xxxxxxxxxx>
pl2303.c doesn't have reset_resume for hibernation.
So needs_binding will be set to 1 duiring hibernation.
usb_forced_unbind_intf will be called, and the port minor
will be released (x in ttyUSBx).
Please use the full 72 columns that you are allowed in a changelog text.
It works fine if you have only one USB-to-serial device.
Assume you have 2 USB-to-serial device, nameing A and B.
A gets a smaller minor(ttyUSB0), B gets a bigger one.
And start to hibernate. When your PC is in hibernation,
unplug device A. Then wake up your PC by pressing the
power button. After waking up the whole system, device
B gets ttyUSB0. This will casuse a problem if you were
using those to ports(like opened two minicom process)
before hibernation.
So member reset_resume is needed in usb_serial_driver
pl2303_device.
If you want persistent device naming, use the symlinks that udev creates
for your for all your serial devices. Never rely on the number of a USB
to serial device.
Let me put it this way. Assume you need to record messages output from two
machines using 2 USB-to-serial devices(naming A and B, and A is on
USB1-port3, B is on USB1-port4) opened by two minicom process.
The setting for A in minicom would be like:
"A - Serial Device : /dev/ttyUSB0"
The setting for B in minicom would be like:
"A - Serial Device : /dev/ttyUSB1"
Then start to hibernate on your computer. When your PC is in
hibernation, unplug A. After waking up your computer, "/dev/ttyUSB0"
would be released first, then allocated to B. The minicom process used
to record outputs from A is now recording B's outputs. The minicom
process used to record outputs from B is now recording nothing, because
"/dev/ttyUSB1" is not exist anymore. That's the problem I've been
talking about. And I don't think using symlinks will solve this problem.
Yes, symlinks will solve the issue, that is what they are there for.
Look in /dev/serial/ for a persistent name for them that allows you to
uniquely open the correct device if they can be described. Using
/dev/ttyUSBX is almost never the correct thing to do.
Thanks for letting me know this. This patch is useless. I still have one
more question though, since using /dev/ttyUSBX is almost never the
correct thing to do, what is /dev/ttyUSBx used for then?
Codes in pl2303_reset_resume are borrowed from pl2303_open.
As a matter of fact, all driver under drivers/usb/serial
has the same problem except ch341.c.
Cc: stable@xxxxxxxxxxxxxxx
How does this meet the stable kernel rule requirements? It would be a
new feature if it were accepted, right?
It's not a new feature at all. struct usb_serial_driver already has a
member name reset_resume, there is no implementation in pl2303.c yet.
And ch341.c has one(ch341_reset_resume()), that why I said "all driver
under drivers/usb/serial has the same problem except ch341.c"
Please read:
https://www.kernel.org/doc/html/latest/process/stable-kernel-rules.html
for what is valid stable kernel changes.
thanks,
greg k-h
thanks,
Hongyu Xie
