linux-kernel - Re: Writing a console/tty driver -- how to use tty

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Date:	Sat, 30 Oct 2010 01:55:13 +0200
From:	Arnd Bergmann <arnd@...db.de>
To:	Alan Cox <alan@...rguk.ukuu.org.uk>
Cc:	Timur Tabi <timur@...escale.com>, gregkh <gregkh@...e.de>,
	lkml <linux-kernel@...r.kernel.org>
Subject: Re: Writing a console/tty driver -- how to use tty_port?

On Friday 29 October 2010, Alan Cox wrote:
> On Thu, 28 Oct 2010 22:57:33 +0200
> Arnd Bergmann <arnd@...db.de> wrote:
> 
> > On Wednesday 27 October 2010 23:04:13 Timur Tabi wrote:
> > > Do you have an updated version of Tiny TTY that uses tty_port structures?  I'm
> > > trying to write a new TTY driver for a device that is not a UART, and I'm having
> > > a hard time finding a good example.  I suspect I need to understand the tty_port
> > > structure, but I can't find any documentation for it.
> > 
> > If the device is not a UART, the best option may be to make the driver
> > a backend to the hvc driver, like e.g. drivers/char/hvc_tile.c.
> > 
> > This works for all devices with or without interrupts that don't need
> > to set up the communication parameters but simply provide a read/write
> > character interface.
> 
> I really don't understand the love of hvc when the hvc drivers seem to be
> bigger than native tty_port code and haul a whole blob of extra midlayer
> glue into the system.
> 

Two reasons for me:

* It does all the timers for the tty device to poll reads and retry writes.
If someone writes similar code from scratch, they most likely get it wrong.

* It's about the simplest interface you can imagine for a new backend driver,
only register a data structure with two function pointers!

	Arnd

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