linux-kernel - Re: Wait for console to become available, v3.2

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Message-Id: <200904210013.48551.david-b@pacbell.net>
Date:	Tue, 21 Apr 2009 00:13:48 -0700
From:	David Brownell <david-b@...bell.net>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	David VomLehn <dvomlehn@...co.com>,
	Arjan van de Ven <arjan@...radead.org>,
	"H. Peter Anvin" <hpa@...or.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Linux USB Mailing List <linux-usb@...r.kernel.org>,
	Linux Embedded Mailing List <linux-embedded@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: Wait for console to become available, v3.2

On Monday 20 April 2009, Ingo Molnar wrote:
> The proper approach would be to use one of the async_synchronize*() 
> facilities in kernel/async.c to properly order the opening of the 
> console with device init.

Stepping back a moment from "how" to make sure "what" is agreed on.

I think I see three scenarios here:

 - Classic PC or server, where there's a meaningful console;

 - Deeply embedded systems, where there isn't;

 - Development stages of "deeply embedded", where there *may* be one.

If that's correct, then async_synchronize() isn't a full answer...

I think a fair number of cases can be papered over with a serial
console with no hardware flow control, which isn't hooked up to
anything.  Maybe the board needs a test/development jig to get one;
without it, the "console" bits spill out into the aether.  Linux
can dump bits to ttyS0, which will act like /dev/null.

But the problem case here seems to be one where such un-hooked-up
serial ports are not realistic options.  Which is why the regression
in USB console functionality has been troublesome.

Is that correct?

- Dave
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