On Mon, Dec 20, 2021 at 09:08:19PM +0800, Jun Miao wrote: > > On 2021/12/20 17:57, gregkh@xxxxxxxxxxxxxxxxxxx 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. 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? > > > 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
