Re: some questions about usb_serial_probe

[Alan Stern <stern@xxxxxxxxxxxxxxxxxxx>]

On Thu, 19 Jul 2012, loody wrote:

> > You didn't look at usb_serial_probe.  At the end of that function there
> I found what you mentioned.
> 	for (i = 0; i < num_ports; ++i) {
> ................
> 		retval = device_add(&port->dev);
> ...................

Yes, that's it.

> > is a loop which runs over all the ports and registers them one at a
> > time with the device layer.  When it is registered, the port is passed
> > to usb_serial_device_probe, which then registers the port with the tty
> > layer.
> The port we pass to usb_serial_device_probe are usb_serial_port
> instead of tty_port, we get it through "to_usb_serial_port(dev);"

Each usb_serial_port contains a tty_port embedded within it.

> in usb_serial_device_probe, it do following things.
> 1. try to call port_probe, which seems do some control for usb_port
> instead of tty port.

The two are pretty much the same thing.  Look through the driver 
sources to see how often "port->port" occurs.

> 2. calling device_create_file(dev, &dev_attr_port_number);
>     dev in above function is embedded in usb_port not in tty_port.
> 3. tty_register_device(usb_serial_tty_driver, minor, dev); this is
> most likely where we register tty port.
> but all three parameters have no relations to tty port.

Well, minor comes from the usb_serial_port, and the tty_port is part of 
the usb_serial_port.

> if above flow is correct, how tty layer know how many tty_ports this
> usb device have?

It doesn't know.  All it knows is that a bunch of tty_port devices have 
been registered; it doesn't know that they all belong to the same USB 
device.

Alan Stern

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