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

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Message-ID: <20170626155115.13617ed6@alans-desktop>
Date:   Mon, 26 Jun 2017 15:51:15 +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 ?

On Mon, 26 Jun 2017 00:43:12 +0200
"Enrico Weigelt, metux IT consult" <enrico.weigelt@...3.net> wrote:

> Hi folks,
> 
> 
> is there already a way for accessing serial ports from drivers,
> w/o having to go through the TTY subsystem ?
> 
> Serdev seems provide a connection between arbitrary TTYs to device
> drivers. But this implies always having a TTY for each UART (even if
> it's never used outside the kernel).
> 
> Is there any way for accessing uarts more directly ?

You can write your own driver for the physical hardware and claim it in
your driver. Shouldn't normally be needed except for bizarre cases when a
serial link is used for something very non tty like (eg as GPIO lines).

Otherwise all the low level tty device locking, queues and interfaces
assume there is a tty_struct attached to it, so yes you need a tty
struct.

Why do you need to do otherwise ?

Alan