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

["andriy.shevchenko@linux.intel.com" <andriy.shevchenko@linux.intel.com>]

On Mon, Dec 20, 2021 at 11:47:14AM +0000, Miao, Jun wrote:
> 发件人: andriy.shevchenko@linux.intel.com <andriy.shevchenko@linux.intel.com>
> 发送时间: 星期一, 十二月 20, 2021 6:46 下午
> On Mon, Dec 20, 2021 at 09:08:19PM +0800, Jun Miao wrote:
> > On 2021/12/20 17:57, gregkh@linuxfoundation.org wrote:
> > > 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 :)
> >
> > Hi maintainer,
> >
> > Thanks your reply so quickly.
> >
> > You mean, this operation is useless and should don`t do that.
> >
> > But , if this is a PNP device,  it can probe successfully after unbind/bind.
> >
> > >
> > > > 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?
> 
> > There is a testcase to test UART by unbind/bind.   i want to support it on
> > old uart  of serial8250 .
> 
> It's fine to perform such test case (and I have done myself many times similar
> operations, but not against PNP UART). Anyway as Greg told you the device is gone
> I'm not sure if there is any kernel version which ever worked with what you are
> suggesting. What you need is to find a device in the sysfs which corresponds your
> PNP UART and perform this against that device.
> 
> I have my examples in the script for non-PNP ones:
> 
> rebind() {
>         local drvdir="/sys/bus/$1/drivers/$2"
>         local devdir="/sys/bus/$1/devices/$3"
>         [ -d "$drvdir" -a -d "$devdir" ] || return
>         echo "$3" > "$drvdir/unbind"
>         echo "$3" > "$drvdir/bind"
> }
> 
> rebind platform 'dw-apb-uart'   '80860F0A:00'   # BYT ttyS1 (ACPI)
> rebind platform 'dw-apb-uart'   '8086228A:00'   # BSW ttyS1 (ACPI)
> rebind pci      '8250_mid'      '0000:00:04.2'  # Edison ttyS1
> rebind pci      'intel-lpss'    '0000:00:18.1'  # BXT LH ttyS1
> rebind pci      'intel-lpss'    '0000:00:1e.0'  # SKL ttyS1
> rebind pci      '8250_lpss'     '0000:00:1e.3'  # BSW ttyS1 (PCI)

> Thanks Andy
> No-pop is not pci,  is only for the old serial8250 PORT ID:0x3F8, which will bind failed.

Yes, I'm aware about that. Please, read carefully what is written above.
It's not a twitter post, it will require more effort to be made to go
through.

-- 
With Best Regards,
Andy Shevchenko