linux-kernel - Re: [PATCH] kernel/printk.c: Concerns about the console handover

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Message-ID: <20070921130600.GB20277@flint.arm.linux.org.uk>
Date:	Fri, 21 Sep 2007 14:06:00 +0100
From:	Russell King <rmk+lkml@....linux.org.uk>
To:	Gerd Hoffmann <kraxel@...hat.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	"Maciej W. Rozycki" <macro@...ux-mips.org>,
	Gerd Hoffmann <kraxel@...e.de>, linux-kernel@...r.kernel.org,
	linux-serial@...r.kernel.org, Yinghai.Lu@....COM,
	bryan.wu@...log.com, dilinger@...ued.net, lethal@...ux-sh.org,
	rgetz@...ckfin.uclinux.org, vapier.adi@...il.com
Subject: Re: [PATCH] kernel/printk.c: Concerns about the console handover

On Fri, Sep 21, 2007 at 02:42:34PM +0200, Gerd Hoffmann wrote:
> Andrew Morton wrote:
> > On Thu, 20 Sep 2007 18:28:49 +0100 (BST) "Maciej W. Rozycki" <macro@...ux-mips.org> wrote:
> > 
> >>  Move the hadover message to after the boot console has been released to 
> >> avoid bad interactions between it and the real console.
> 
> [ longish problem discussion snipped ]
> 
> >> considered fully disabled.  Below is a change which makes the problem 
> >> disappear for me, but I suppose there was a deliberate reason for placing 
> >> the printk() where it is now and nowhere else.
> 
> Well, I placed the printk there is for user interface reasons.  I think
> especially in case the early console and the real console go to
> different physical devices it is useful to have the reason it stops
> printing messages displayed on the early console.  So people don't think
> the computer hangs although it just prints messages elsewhere ...
> 
> If that isn't going to work due to two instances not knowing each other
> (kernel & firmware) should not mess with the same physical device, then
> I'd just drop the printk.  And I see no pretty and easy way around that
> issue :-(
> 
> We could do the printk and unregister before we setup the new console.
> Which has the drawback that we are in trouble in case the setup() call
> for the new console fails ...
> 
> We could split the printk into two, one early ("trying to setup new
> console foo") which goes to the boot console, then (assuming the setup
> worked ok) unregister silently and print a message about the successful
> init and boot console unregister on the new console only.  Which results
> in two lines being printed for the handover when both consoles address
> the same physical device.  Not that nice IMHO, but maybe still the best
> way to handle it.

I had an issue with the console initialisation on serial ports, which I
discovered during my PXA work.  My reason for asking about the kernel
versions (which Andrew forwarded to LKML) is to determine whether the
report is as a result of those changes, or lack of those changes.

Those -mm versions with git-arm in probably have that change.  Ergo
the importance to answer this question about kernel versions.

-- 
Russell King
 Linux kernel    2.6 ARM Linux   - http://www.arm.linux.org.uk/
 maintainer of:
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