linux-kernel - Re: [PATCH 1/2] time: Serialize calls to 'clockevents_update

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Date:	Wed, 11 Dec 2013 12:09:04 -0800
From:	Sören Brinkmann <soren.brinkmann@...inx.com>
To:	Daniel Lezcano <daniel.lezcano@...aro.org>
CC:	Thomas Gleixner <tglx@...utronix.de>,
	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>,
	<linux-kernel@...r.kernel.org>,
	<linux-arm-kernel@...ts.infradead.org>,
	<devicetree@...r.kernel.org>
Subject: Re: [PATCH 1/2] time: Serialize calls to 'clockevents_update_freq'
 in the timing core

Hi Daniel,

On Wed, Dec 11, 2013 at 03:32:57PM +0100, Daniel Lezcano wrote:
> On 12/10/2013 01:34 AM, Soren Brinkmann wrote:
> >From: Thomas Gleixner <tglx@...utronix.de>
> >
> >We can identify the broadcast device in the core and serialize all
> >callers including interrupts on a different CPU against the update.
> >Also, disabling interrupts is moved into the core allowing callers to
> >leave interrutps enabled when calling clockevents_update_freq().
> >
> >Cc: Thomas Gleixner <tglx@...utronix.de>
> >Signed-off-by: Soren Brinkmann <soren.brinkmann@...inx.com>
> >---
> >  kernel/time/clockevents.c    | 29 ++++++++++++++++++++++-------
> >  kernel/time/tick-broadcast.c | 25 +++++++++++++++++++------
> >  kernel/time/tick-internal.h  |  4 ++++
> >  3 files changed, 45 insertions(+), 13 deletions(-)
> >
> >diff --git a/kernel/time/clockevents.c b/kernel/time/clockevents.c
> >index 086ad6043bcb..641d91003a45 100644
> >--- a/kernel/time/clockevents.c
> >+++ b/kernel/time/clockevents.c
> >@@ -439,6 +439,16 @@ void clockevents_config_and_register(struct clock_event_device *dev,
> >  }
> >  EXPORT_SYMBOL_GPL(clockevents_config_and_register);
> >
> >+int __clockevents_update_freq(struct clock_event_device *dev, u32 freq)
> >+{
> >+	clockevents_config(dev, freq);
> >+
> >+	if (dev->mode != CLOCK_EVT_MODE_ONESHOT)
> >+		return 0;
> >+
> >+	return clockevents_program_event(dev, dev->next_event, false);
> >+}
> >+
> 
> ./arch/arm/kernel/smp_twd.c should be modified to call
> __clockevents_update_freq instead of clockevents_update_freq, no ?

IIUC, the __-version is only for timer core internal usage and not an
exported interface. Doesn't the non-__ version work for the twd?
I don't see issues on my Zynq platform with these patches.

Another side note regarding the twd: Shouldn't we set the
CLOCK_EVT_FEAT_PERCPU flag we introduced recently for that timer?

	Sören


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