linux-kernel - Re: [PATCH v2 4/9] clocksource/cadence_ttc: Use enable/disable

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Date:	Thu, 28 Nov 2013 12:55:38 +0100
From:	Daniel Lezcano <daniel.lezcano@...aro.org>
To:	Soren Brinkmann <soren.brinkmann@...inx.com>,
	Rob Herring <rob.herring@...xeda.com>,
	Pawel Moll <pawel.moll@....com>,
	Mark Rutland <mark.rutland@....com>,
	Stephen Warren <swarren@...dotorg.org>,
	Ian Campbell <ijc+devicetree@...lion.org.uk>,
	Russell King <linux@....linux.org.uk>,
	Michal Simek <michal.simek@...inx.com>,
	Thomas Gleixner <tglx@...utronix.de>
CC:	linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	devicetree@...r.kernel.org
Subject: Re: [PATCH v2 4/9] clocksource/cadence_ttc: Use enable/disable_irq

On 11/27/2013 02:04 AM, Soren Brinkmann wrote:
> To ensure that the timer interrupt is properly enabled/disabled across
> the whole CPU cluster use enable/disable_irq() instead of
> local_irq_disable().
>
> Signed-off-by: Soren Brinkmann <soren.brinkmann@...inx.com>
> ---
>   drivers/clocksource/cadence_ttc_timer.c | 6 ++----
>   1 file changed, 2 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/clocksource/cadence_ttc_timer.c b/drivers/clocksource/cadence_ttc_timer.c
> index a92350b55d32..246d018d1e63 100644
> --- a/drivers/clocksource/cadence_ttc_timer.c
> +++ b/drivers/clocksource/cadence_ttc_timer.c
> @@ -322,18 +322,16 @@ static int ttc_rate_change_clockevent_cb(struct notifier_block *nb,
>   	switch (event) {
>   	case POST_RATE_CHANGE:
>   	{
> -		unsigned long flags;
> -
>   		/*
>   		 * clockevents_update_freq should be called with IRQ disabled on
>   		 * the CPU the timer provides events for. The timer we use is
>   		 * common to both CPUs, not sure if we need to run on both
>   		 * cores.
>   		 */
> -		local_irq_save(flags);
> +		disable_irq(ttcce->ce.irq);
>   		clockevents_update_freq(&ttcce->ce,
>   				ndata->new_rate / PRESCALE);
> -		local_irq_restore(flags);
> +		enable_irq(ttcce->ce.irq);
>
>   		/* update cached frequency */
>   		ttc->freq = ndata->new_rate;
>

I am worried about the 'disable_irq' function calling 'synchronize_irq'. 
Isn't possible to deadlock with the ondemand cpufreq governor ? I added 
Viresh in Cc, he knows better than me the code path.

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