linux-kernel - Re: [PATCH] i486 CR4 oops, no_console

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Message-ID: <20080819093454.GG28713@elte.hu>
Date:	Tue, 19 Aug 2008 11:34:54 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	David Fries <david@...es.net>
Cc:	linux-kernel@...r.kernel.org, "Rafael J. Wysocki" <rjw@...k.pl>,
	Pavel Machek <pavel@....cz>, "H. Peter Anvin" <hpa@...or.com>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH] i486 CR4 oops, no_console_suspend


* David Fries <david@...es.net> wrote:

> On Mon, Aug 18, 2008 at 08:41:20AM +0200, Ingo Molnar wrote:
> > 
> > applied to tip/x86/urgent, thanks David. I've changed the conditions 
> > to read_cr4_safe() instead - that's cleaner. Could you please check 
> > whether the patch below works fine too on your box?
> 
> Yes the 486 suspends and resumes with this patch.

good - it's now upstream and should show up in 2.6.27-rc4 as well.

> Is there any known problem with no_console_suspend and serial 
> consoles?  It worked to print the oops for me to track this down, and 
> Documentation/kernel-parameters.txt says it is known to work with 
> serial consoles, but on resume only kernel messages can output to the 
> serial console.  The getty on the serial port can't raed or write and 
> processes trying to write to the port just hang without getting any 
> data across.  The serial port works fine across suspends without the 
> no_console_suspend argument.  Does anyone else see this?

i've had trouble no end with getting even kernel messages out to the 
serial console during critical phases of suspend/resume. (especially in 
combination with earlyprintk=ttyS0 - not surprisingly)

Especially during resume the UART is initialized back to something 
really slow - 300 bauds or 9600 bauds. (depends on the chipset i guess) 
So even though it works, it will only worked reliably when i 
standardized all my baud settings to that very low setting.

	Ingo
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