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

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Message-ID: <20070921134331.GC20277@flint.arm.linux.org.uk>
Date:	Fri, 21 Sep 2007 14:43:32 +0100
From:	Russell King <rmk+lkml@....linux.org.uk>
To:	"Maciej W. Rozycki" <macro@...ux-mips.org>
Cc:	Andrew Morton <akpm@...ux-foundation.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, kraxel@...hat.com,
	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 02:36:50PM +0100, Maciej W. Rozycki wrote:
> On Fri, 21 Sep 2007, Andrew Morton wrote:
> 
> > It would be useful to have some basic information like: Which kernel
> > version was this found in?  Which kernel version last worked?
> 
>  The kernel used was a 2.6.23-rc5 snapshot from Sep 4th, 2007 taken from 
> the linux-mips.org tree (as stated by the revision of the patch provided).  
> There is no version that can be considered working as the change to add 
> the printk() to register_console() went in before drivers/serial/zs.c was 
> added and the old drivers/tc/zs.c driver might have been to sloppy to 
> handle such bits as the transmitter enable properly.  I may investigate.
> 
>  Chances are nobody tried any version of the kernel from the period 
> between the printk() was added and drivers/tc/zs.c removed with the 
> DECstation; I have not.
> 
>  Anyway, I did confirm keeping the transmitter enabled all the time makes 
> the problem go away.

I suspect the correct fix for this is to take the fix in the ARM tree
for serial_core's console initialisation, and ensure that zs.c handles
the power management of the port (enabling/disabling transmitter)
in the power management callback.

You can find the fix in the mbox archive:

 http://ftp.arm.linux.org.uk/pub/linux/arm/kernel/git-cut/arm:devel.mbox

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