Re: [PATCH] USB: serial: Support attaching serdev devices

[Alban Bedel <alban.bedel@lht.dlh.de>]

On Thu, 17 Sep 2026 09:27:42 +0100
Greg Kroah-Hartman <gregkh@linuxfoundation.org> wrote:

> On Thu, Sep 17, 2026 at 10:11:03AM +0200, Alban Bedel wrote:
> > Use tty_port_register_device_serdev() to allow attaching serdev
> > devices to USB serial ports. Also set the ACPI companion device on the
> > USB serial device to let the serdev matching work on ACPI systems.  
> 
> "also" should be a separate patch, right?

Will do.

> And I didn't think that serdev could handle devices going away at any
> point in time, when did that change?  How was this all tested and what
> ACPI device wants to use this?

The use case here is an x86 embedded platform with a soldered USB serial
adapter connecting to a MAX9265 GMSL serializer. As everything is on a
single PCB there is no question of anything getting disconnected at
runtime.

But I now see that I missed that the bus remove also need to be
adjusted to use tty_port_unregister_device() instead of
tty_unregister_device().  With that done the serdev device get properly
taken down when I manually disable the port. With a small fix to the
serdev core it also comes back up when the port is enabled again.

The ACPI part is a custom DSDT overlay that defines the chain
starting from the USB port. At this level there is no difference to 
classic UART where serdev are already working.

Alban