linux-kernel - Re: How do I choose an arbitrary minor number for my tty device?

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Message-ID: <4CEA9B00.1000804@freescale.com>
Date:	Mon, 22 Nov 2010 10:32:00 -0600
From:	Timur Tabi <timur@...escale.com>
To:	Alan Cox <alan@...rguk.ukuu.org.uk>
CC:	Greg KH <gregkh@...e.de>, Arnd Bergmann <arnd@...db.de>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Scott Wood <scottwood@...escale.com>,
	Stuart Yoder <stuart.yoder@...escale.com>
Subject: Re: How do I choose an arbitrary minor number for my tty device?

Alan Cox wrote:
>> > Is there a way to do it in the driver itself?  Getting the boot loader to
>> > identify the specific byte channel for stdout isn't trivial.  It'd be nice if
>> > the driver could tell the tty layer, "BTW, this use this for the default console".

> You can - provide the required method in your console driver and it'll
> get used by /dev/console. Funnily enough a lot of other platform and
> consoles need that too.

Can you elaborate on that?  What is the "required method"?  My driver is mostly
working now, but I have to supply the command-line "console=ttyEHV73" in order
for the login prompt to show up.  Unfortunately, there's no way for the boot
loader to know that the primary byte channel for stdout is #73, so I need a way
for the driver to tell the kernel this.

Also, if I have a /dev/ttyEHV76 entry for a byte channel that's not the primary
stdout tty, is the following supposed to work:

	cat > /dev/ttyEHV76

That is, should I be able to use a TTY device as a normal character device,
where I can just write and read characters?

-- 
Timur Tabi
Linux kernel developer at Freescale

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