Re: [BUG report]: serial8250 unbind/bind failture

On Mon, Dec 20, 2021 at 09:08:19PM +0800, Jun Miao wrote:

On 2021/12/20 17:57, gregkh@linuxfoundation.org wrote:

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On Mon, Dec 20, 2021 at 09:54:41AM +0000, Miao, Jun wrote:

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[Hardware]
Intel Corporation Alder Lake Client Platform/AlderLake-M LP5 RVP, BIOS ADLPFWI1.R00.2265.A01.2107010436 07/01/2021
About x86 old UART, not the PNP device.

[how to reproduce]
root@ALD-M:/sys/devices/platform/serial8250/tty/ttyS0/device/driver# echo -n "serial8250" > unbind
root@ALD-M:/sys/devices/platform/serial8250/tty/ttyS0/device/driver# echo -n "serial8250" > bind

After you unbound, this device is gone, so how does this path still
work?

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[What`s my Confusion]
After the unbind and bind the serial8250_probe cannot register ttyS0.

Then do not do that :)

Hi maintainer,

Thanks your reply so quickly.

You mean, this operation is useless and should don`t do that.

Why do you think it is useful?

But , if this is a PNP device,  it can probe successfully after unbind/bind.

Is that possible?  If so, how?  Has it ever worked before?  Who requires
this to work?  Does this bus and hardware support this type of
functionality for this hardware device?

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And there is not dmesg like this: "serial8250: ttyS0 at I/O 0x3f8 (irq = 4, base_baud = 115200) is a 16550A".

Any one have some advice about 8250 serial ?  It is a common operation if we believe that the old UART which don`t support like this unbind. Or we ignore about this really bug before?

What are you trying to do here exactly?  Why are you wanting to unbind
the driver from this device?  Why do you then want to bind it again?
What problem are you trying to solve by doing this?

thanks,

greg k-h

There is a testcase to test UART by unbind/bind.   i want to support it on
old uart  of serial8250 .

Who created this test case and what were they expecting to have happen?
What are they thinking this test case should be doing?  Is this a new
functionality that they need Linux to support?  If so, then new code
probably has to be written :)

bind/unbind is a "best effort" type of thing, not all busses and
hardware types support this at all.

thanks,

greg k-h