Curious about tty_port_operations drop() callback.

[Grant Edwards <grant.b.edwards@gmail.com>]

While testing/debugging the tty driver I've changed to use the
tty_port_* helper functions, I noticed there are two
tty_port_operation fields that I'm not providing: destruct() and
drop(). There's an example of destruct() usage in the hvc driver and a
comment in tty.h explaining when it's called, so that's fairly
obvious.

I haven't been able to figure out the purpose of the drop() callback.
It's not used anywhere and there is no comment in tty.h hinting at its
purpose.

Looking at tty_port_close() shows that drop() is called during close()
of port with a reference count > 1.  IOW, close() calls drop() in the
cases where it isn't going to call shutdown().

There doesn't seem to be a corresponding "raise" callback during
open() when activate() isn't going to be called, and I can't think of
any use for either drop or raise...

-- 
Grant Edwards               grant.b.edwards        Yow! My mind is a potato
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