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

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Message-Id: <200810280920.19864.david-b@pacbell.net>
Date:	Tue, 28 Oct 2008 09:20:19 -0700
From:	David Brownell <david-b@...bell.net>
To:	Haavard Skinnemoen <haavard.skinnemoen@...el.com>
Cc:	lkml <linux-kernel@...r.kernel.org>,
	Haavard Skinnemoen <hskinnemoen@...el.com>,
	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

On Tuesday 28 October 2008, Haavard Skinnemoen wrote:
> David Brownell <david-b@...bell.net> wrote:
> > From: David Brownell <dbrownell@...rs.sourceforge.net>
> > 
> > The atmel_serial driver is mismanaging its clock by leaving it on
> > at all times ... the whole point of clock management is to leave
> > it off unless it's actively needed, which conserves power!!
> > 
> > Signed-off-by: David Brownell <dbrownell@...rs.sourceforge.net>
> 
> Hmm...the only remaining clk_enable() is in atmel_serial_pm(). Is that
> really enough?
> 
> It looks like the serial core calls ->pm() to power the port up before
> doing anything that might touch the registers, but I can't see that the
> console layer does the same thing...

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.  :)

- Dave


> 
> Haavard
> 
> 


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