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

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Message-ID: <51C8B551.9080203@st.com>
Date:	Mon, 24 Jun 2013 22:08:33 +0100
From:	Srinivas KANDAGATLA <srinivas.kandagatla@...com>
To:	Stephen Boyd <sboyd@...eaurora.org>
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 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);
}

 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.



Thanks,
srini
> 

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