linux-kernel - Re: [PATCH v5] clocksource:arm_global_timer: Add ARM global timer support.

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Message-ID: <51C8C172.8020207@codeaurora.org>
Date:	Mon, 24 Jun 2013 15:00:18 -0700
From:	Stephen Boyd <sboyd@...eaurora.org>
To:	srinivas.kandagatla@...com
CC:	John Stultz <john.stultz@...aro.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Grant Likely <grant.likely@...aro.org>,
	Rob Herring <rob.herring@...xeda.com>,
	Rob Landley <rob@...dley.net>,
	devicetree-discuss@...ts.ozlabs.org, linux-doc@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	Linus Walleij <linus.walleij@...aro.org>,
	Stuart Menefy <stuart.menefy@...com>,
	Arnd Bergmann <arnd@...db.de>,
	Rob Herring <robherring2@...il.com>,
	Will Deacon <will.deacon@....com>
Subject: Re: [PATCH v5] clocksource:arm_global_timer: Add ARM global timer
 support.

On 06/24/13 14:08, Srinivas KANDAGATLA wrote:
> On 24/06/13 21:06, Stephen Boyd wrote:
>> On 06/24/13 08:53, Srinivas KANDAGATLA wrote:
>>> +
>>> +static void gt_clockevents_stop(struct clock_event_device *clk)
>>> +{
>>> +	gt_clockevent_set_mode(CLOCK_EVT_MODE_UNUSED, clk);
>>> +	disable_percpu_irq(clk->irq);
>>> +}
>>> +
>>> +static int __cpuinit gt_clockevents_setup(struct clock_event_device *clk)
>>> +{
>>> +	struct clock_event_device *evt = this_cpu_ptr(gt_evt);
>>> +	return evt->name ? 0 : gt_clockevents_init(evt);
>>> +}
>> How does this work? gt_clockevents_stop() is using the
>> clock_event_device struct from the ARM local timer layer whereas
>> gt_clockevents_setup() is using a driver private allocation.
> Thanks for pointing this..
> This should fix it.
>
> static void gt_clockevents_stop(struct clock_event_device *clk)
> {
> 	struct clock_event_device *evt = this_cpu_ptr(gt_evt);
> 	gt_clockevent_set_mode(CLOCK_EVT_MODE_UNUSED, evt);
> 	disable_percpu_irq(evt->irq);
> }

Looks good, but even better would be to not use the local timer API.

>  Please just
>> don't use the local timer API at all and use cpu notifiers instead.
> Last time when I did try using cpu notifiers like arm_arch_timer, the
> broadcast dummy timer did kick off and took over the local timer on the
> secondary cpus. Resulting in lot of broadcast IPI's.
>
> If I use cpu notifiers I will end up two clk events on a each core (one
> dummy from arm/kernel/smp.c and other gt clk_evt). I think I can only
> use cpu notifiers in my case once your patches are in.
> Also I cant disable LOCAL_TIMERS as it y by default.
>
> Am I missing something?
>
> Am happy to move to cpu notifiers if it works, else the driver will be
> broken.

I think the problem is your clockevent has no rating. Please give it a
rating (300?) so that it prevents the dummy from taking over. You don't
need to worry about disabling the local timer API, it will register a
harmless clockevent with a low rating (100) that should be ignored.

-- 
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