From: u.kleine-koenig@pengutronix.de (Uwe =?iso-8859-1?Q?Kleine-K=F6nig?=)
Date: Fri, 7 Jun 2013 09:49:41 +0200
Subject: [PATCH 1/1] ARM: imx: clk-pllv3: change wait method for PLL lock
In-Reply-To: <20130607033306.GC21641@nchen-desktop>
References: <1370501726-7421-1-git-send-email-peter.chen@freescale.com>
 <20130606121647.GR23140@pengutronix.de>
 <20130607025320.GA21641@nchen-desktop>
 <20130607033306.GC21641@nchen-desktop>
Message-ID: <20130607074941.GD12361@pengutronix.de>
To: linux-arm-kernel@lists.infradead.org
List-Id: linux-arm-kernel.lists.infradead.org

On Fri, Jun 07, 2013 at 11:33:07AM +0800, Peter Chen wrote:
> On Fri, Jun 07, 2013 at 10:53:20AM +0800, Peter Chen wrote:
> > On Thu, Jun 06, 2013 at 02:16:47PM +0200, Uwe Kleine-K?nig wrote:
> > > Hello
> > > 
> > > [added jstultz to Cc:]
> > > 
> > > On Thu, Jun 06, 2013 at 02:55:26PM +0800, Peter Chen wrote:
> > > > For tickless system, the jiffies may be updated long time (>20ms).
> > > ... may not be updated for a long time ... ?
> > > 
> > > > At high loading system, the current waiting method will cause waiting
> > > > timeout, and cause a kernel dump at below case.
> > > > After timeout = jiffies + msecs_to_jiffies(10),
> > > > the timer interrupt occurs, it updates jiffies (eg,  + 2 jiffies),
> > > > then return back from interrupt, the time between above operations
> > > > are tiny, the PLL is still not locked, but the timeout condition is satisfied.
> > > Hmm, I admit I didn't follow the tickless stuff, but still I wonder if
> > > the analysis is right. I thought on tickless jiffies are updated as
> > > before by the boot cpu that cannot run in tickless mode?
> > > 
> > > Anyhow, this only affects the commit log, not the problem.
> > >  
> > 
> > I add jiffies print at irq_exit (kernel/softirq.c), and it
> > is not updated every jiffies.
> 
> Oh, I have not considered cpu idle condition. I think this
> problem may occur the condition that irq and softirq consume
> too much time.
That was my thought, too. With my patch this time at least only happens
after the pll is programmed and the issue might be solved, too?! (Maybe
apart from Russell's comment.)

Best regards
Uwe

-- 
Pengutronix e.K.                           | Uwe Kleine-K?nig            |
Industrial Linux Solutions                 | http://www.pengutronix.de/  |