linux-kernel - Re: Enable arm_global_timer for Zynq brakes boot

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Message-ID: <51F77D93.4030505@linaro.org>
Date:	Tue, 30 Jul 2013 10:47:15 +0200
From:	Daniel Lezcano <daniel.lezcano@...aro.org>
To:	Sören Brinkmann <soren.brinkmann@...inx.com>
CC:	Stephen Boyd <sboyd@...eaurora.org>,
	John Stultz <john.stultz@...aro.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Stuart Menefy <stuart.menefy@...com>,
	Russell King <linux@....linux.org.uk>,
	Michal Simek <michal.simek@...inx.com>,
	linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org
Subject: Re: Enable arm_global_timer for Zynq brakes boot

On 07/30/2013 02:03 AM, Sören Brinkmann wrote:
> Hi Daniel,
> 
> On Mon, Jul 29, 2013 at 02:51:49PM +0200, Daniel Lezcano wrote:
> (snip)
>>
>> the CPUIDLE_FLAG_TIMER_STOP flag tells the cpuidle framework the local
>> timer will be stopped when entering to the idle state. In this case, the
>> cpuidle framework will call clockevents_notify(ENTER) and switches to a
>> broadcast timer and will call clockevents_notify(EXIT) when exiting the
>> idle state, switching the local timer back in use.
> 
> I've been thinking about this, trying to understand how this makes my
> boot attempts on Zynq hang. IIUC, the wrongly provided TIMER_STOP flag
> would make the timer core switch to a broadcast device even though it
> wouldn't be necessary. But shouldn't it still work? It sounds like we do
> something useless, but nothing wrong in a sense that it should result in
> breakage. I guess I'm missing something obvious. This timer system will
> always remain a mystery to me.
> 
> Actually this more or less leads to the question: What is this
> 'broadcast timer'. I guess that is some clockevent device which is
> common to all cores? (that would be the cadence_ttc for Zynq). Is the
> hang pointing to some issue with that driver?

If you look at the /proc/timer_list, which timer is used for broadcasting ?

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