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Date:   Mon, 20 Dec 2021 10:57:24 +0100
From:   "gregkh@linuxfoundation.org" <gregkh@linuxfoundation.org>
To:     "Miao, Jun" <jun.miao@intel.com>
Cc:     "andriy.shevchenko@linux.intel.com" 
        <andriy.shevchenko@linux.intel.com>,
        "linux-serial@vger.kernel.org" <linux-serial@vger.kernel.org>
Subject: Re: [BUG report]: serial8250 unbind/bind failture
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On Mon, Dec 20, 2021 at 09:54:41AM +0000, Miao, Jun wrote:
> [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?

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

Then do not do that :)

> 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