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clocksource: Add generic dummy timer driver

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Several architectures have a dummy timer driver tightly coupled with
their broadcast code to support machines without cpu-local timers (or
where there is a lack of driver support).

Since 12ad100046: "clockevents: Add generic timer broadcast function"
it's been possible to write broadcast-capable timer drivers decoupled
from the broadcast mechanism. We can use this functionality to implement
a generic dummy timer driver that can be shared by all architectures
with generic tick broadcast (ARCH_HAS_TICK_BROADCAST).

This patch implements a generic dummy timer using this facility.

[sboyd: Make percpu data static, use __this_cpu_ptr(), move to
        early_initcall to properly register on each CPU, only
	register if more than one CPU possible]

Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>
Acked-by: Marc Zyngier <marc.zyngier@arm.com>,
Cc: John Stultz <john.stultz@linaro.org>
Cc: Daniel Lezcano <daniel.lezcano@linaro.org>
Cc: linux-arm-kernel@lists.infradead.org
Link: http://lkml.kernel.org/r/1370291642-13259-3-git-send-email-sboyd@codeaurora.org
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
This commit is contained in:
Mark Rutland 2013-06-03 13:33:53 -07:00 committed by Thomas Gleixner
parent 70e5975d3a
commit 064706514e
2 changed files with 70 additions and 0 deletions
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1
drivers/clocksource/Makefile
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@ -31,3 +31,4 @@ obj-$(CONFIG_VF_PIT_TIMER) += vf_pit_timer.o
obj-$(CONFIG_ARM_ARCH_TIMER) += arm_arch_timer.o
obj-$(CONFIG_CLKSRC_METAG_GENERIC) += metag_generic.o
obj-$(CONFIG_ARCH_HAS_TICK_BROADCAST) += dummy_timer.o

69
drivers/clocksource/dummy_timer.c Normal file
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@ -0,0 +1,69 @@
/*
* linux/drivers/clocksource/dummy_timer.c
*
* Copyright (C) 2013 ARM Ltd.
* All Rights Reserved
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License version 2 as
* published by the Free Software Foundation.
*/
#include <linux/clockchips.h>
#include <linux/cpu.h>
#include <linux/init.h>
#include <linux/percpu.h>
#include <linux/cpumask.h>
static DEFINE_PER_CPU(struct clock_event_device, dummy_timer_evt);
static void dummy_timer_set_mode(enum clock_event_mode mode,
struct clock_event_device *evt)
{
/*
* Core clockevents code will call this when exchanging timer devices.
* We don't need to do anything here.
*/
}
static void __cpuinit dummy_timer_setup(void)
{
int cpu = smp_processor_id();
struct clock_event_device *evt = __this_cpu_ptr(&dummy_timer_evt);
evt->name = "dummy_timer";
evt->features = CLOCK_EVT_FEAT_PERIODIC |
CLOCK_EVT_FEAT_ONESHOT |
CLOCK_EVT_FEAT_DUMMY;
evt->rating = 100;
evt->set_mode = dummy_timer_set_mode;
evt->cpumask = cpumask_of(cpu);
clockevents_register_device(evt);
}
static int __cpuinit dummy_timer_cpu_notify(struct notifier_block *self,
unsigned long action, void *hcpu)
{
if ((action & ~CPU_TASKS_FROZEN) == CPU_STARTING)
dummy_timer_setup();
return NOTIFY_OK;
}
static struct notifier_block dummy_timer_cpu_nb __cpuinitdata = {
.notifier_call = dummy_timer_cpu_notify,
};
static int __init dummy_timer_register(void)
{
int err = register_cpu_notifier(&dummy_timer_cpu_nb);
if (err)
return err;
/* We won't get a call on the boot CPU, so register immediately */
if (num_possible_cpus() > 1)
dummy_timer_setup();
return 0;
}
early_initcall(dummy_timer_register);