linux-kernel - Re: Directly accessing serial ports from drivers w/o TTYs ?

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Date:   Fri, 30 Jun 2017 18:23:55 +0100
From:   Alan Cox <gnomes@...rguk.ukuu.org.uk>
To:     "Enrico Weigelt, metux IT consult" <enrico.weigelt@...3.net>
Cc:     linux-kernel@...r.kernel.org
Subject: Re: Directly accessing serial ports from drivers w/o TTYs ?

> I was thinking about something that looks like serdev from consumer
> side, but instead directly works on struct uart_port, w/o actually
> allocating a tty (and also the funny things like signals, etc).

uart_port is only a subset of tty devices and also relies upon tty for
some of the locking and other behaviour.

> > Why do you need to do otherwise ?  
> 
> Maybe it could offer better performance ?

Unless you have very tight latency requirements I would be surprised if
you could do that much better even on a slow machine. If you don't need
tty semantics then you can probably beat it hands down by writing your
own custom driver for the hardware that doesn't pretend to be a tty in
the first place.

The cost in the tty stack is pretty much all the Unix tty API and POSIX
guarantees.

Alan