linux-kernel - Re: [patch 2.6.28-rc2] atmel_serial: keep clock off when it's not needed

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Message-ID: <20081028184857.030d029a@hskinnemo-gx745.norway.atmel.com>
Date:	Tue, 28 Oct 2008 18:48:57 +0100
From:	Haavard Skinnemoen <haavard.skinnemoen@...el.com>
To:	David Brownell <david-b@...bell.net>
Cc:	lkml <linux-kernel@...r.kernel.org>,
	Nicolas Ferre <nicolas.ferre@....atmel.com>,
	Andrew Victor <linux@...im.org.za>
Subject: Re: [patch 2.6.28-rc2] atmel_serial: keep clock off when it's not
 needed

David Brownell <david-b@...bell.net> wrote:
> > > I verified it on AT91, where the console is normally DBGU and the
> > > other USARTs do get an open().
> > > 
> > > Didn't verify on AVR32, since 2.6.28-rc can't see the root FS because
> > > of that NOR flash problem.  Though I suppose I can try it on an older
> > > kernel.
> > > 
> > > As a rule the boot loader will be using that USART, and thus will
> > > have enabled its clock.  :)  
> > 
> > Hmm. But in the cases when "normally" and "as a rule" don't apply, the
> > board will lock up solid with no console output since it will wait
> > forever for the TXRDY bit to be set...
> > 
> > I'd like to know for sure that it cannot happen, please.  
> 
> I'd just like to know that this bug is fixed.  Do you have a
> better fix?  (And a board broken by this patch, to verify it?)

Fixing a bug by introducing a worse one isn't much of an improvement.
The bug may be difficult to trigger, but that makes it even worse,
IMO.

I'll see if I can come up with a fix. Basically, we need to enable the
clock when initializing the console, and disable it after calling
uart_add_one_port() if the port is the console.

Haavard
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