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

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Message-ID: <20090422220853.0af12ece@lxorguk.ukuu.org.uk>
Date:	Wed, 22 Apr 2009 22:08:53 +0100
From:	Alan Cox <alan@...rguk.ukuu.org.uk>
To:	David VomLehn <dvomlehn@...co.com>
Cc:	Alan Stern <stern@...land.harvard.edu>,
	Jamie Lokier <jamie@...reable.org>,
	Ingo Molnar <mingo@...e.hu>,
	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

> Alright, I know you (Alan (Stern)) know about USB. I think someone else
> mentioned Firewire. What other hotpluggable buses do we need to worry about
> and how can we get them interested?

In theory any console can be hot pluggable - PCI-X hotplug video cards,
hotplug serial ports. In fact right now bad things occur if you
hot-unplug consoles.

> 2.	All devices have been probed
> If we exit for reason 2, it means that no such device is present,
> and we go on to the do the appropriate thing for that device class.

USB has no notion of #2 really

> Yes, I think we absolutely exclude devices plugged in after boot. I think such
> usage, if it needs to be supported, can be handled with hot plugging. I'm a
> little squishy on whether we might to be able to hot plug USB consoles as I
> have a request to support this, but I think it's a separate issue from
> supporting hot pluggable boot devices and I'm not worrying about it now.

This still assumes you can tell the difference, but USB in particular is
rather like undergraduate students - they turn up when they feel like it
at some point after they get kicked into life.

I don't think that is a big problem because our bus model is basically
that all devices are discovered asynchronously (increasingly so with
Arjan's speed up patches). A console model therefore has to deal with
console addition and removal being dynamic.
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