On Fri, Feb 22, 2013 at 04:25:00PM +0000, Paul Mundt wrote:
> On Fri, Feb 22, 2013 at 11:15:45AM +0000, Mark Rutland wrote:
> > One thing that struck me when I was fiddling with the broadcast mechanism was
> > that it should be possible to have a generic dummy timer implementation. As
> > long as the architecture calls notifiers at the appropriate times, it should
> > look like any other timer driver (apart from not touching any hardware). It just
> > needs to depend on ARCH_HAS_TICK_BROADCAST.
> >
> > I believe it shouldn't be too difficult to implement, though I may be blind to
> > some problems.
> >
> It would be nice to have a generic dummy timer driver, quite a few
> architectures could use it directly already. If no one beats me to it,
> I'll give it a go as I convert the SH stuff over to using
> ARCH_HAS_TICK_BROADCAST and killing off the local timer API there.
>
I've had a quick go at writing a generic timer driver. I've not had a chance to
test it, and there are a couple of things that are up for discussion (e.g. what
should the rating be) but I think we want something very close to this.
Thanks,
Mark.
---->8----
>From 1ca7fdf68fbb9b026237803db8c55a34b4f2cfa2 Mon Sep 17 00:00:00 2001
From: Mark Rutland <mark.rutland@xxxxxxx>
Date: Sun, 24 Feb 2013 22:31:24 +0000
Subject: [PATCH] clocksource: add generic dummy timer driver
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.
Signed-off-by: Mark Rutland <mark.rutland@xxxxxxx>
---
drivers/clocksource/Makefile | 1 +
drivers/clocksource/dummy_timer.c | 67 +++++++++++++++++++++++++++++++++++++++
2 files changed, 68 insertions(+)
create mode 100644 drivers/clocksource/dummy_timer.c
diff --git a/drivers/clocksource/Makefile b/drivers/clocksource/Makefile
index 7d671b8..8f2b13f 100644
--- a/drivers/clocksource/Makefile
+++ b/drivers/clocksource/Makefile
@@ -21,3 +21,4 @@ obj-$(CONFIG_ARCH_TEGRA) += tegra20_timer.o
obj-$(CONFIG_VT8500_TIMER) += vt8500_timer.o
obj-$(CONFIG_ARM_ARCH_TIMER) += arm_arch_timer.o
+obj-$(CONFIG_ARCH_HAS_TICK_BROADCAST) += dummy_timer.o
diff --git a/drivers/clocksource/dummy_timer.c b/drivers/clocksource/dummy_timer.c
new file mode 100644
index 0000000..bdaba34
--- /dev/null
+++ b/drivers/clocksource/dummy_timer.c
@@ -0,0 +1,67 @@
+/*
+ * 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>
+
+DEFINE_PER_CPU(struct clock_event_device, dummy_evt);
+
+static void dummy_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_setup(void)
+{
+ int cpu = smp_processor_id();
+ struct clock_event_device *evt = &per_cpu(dummy_evt, cpu);
+
+ 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_set_mode;
+ evt->cpumask = cpumask_of(cpu);
+
+ clockevents_register_device(evt);
+}
+
+static int __cpuinit dummy_cpu_notify(struct notifier_block *self,
+ unsigned long action, void *hcpu)
+{
+ if ((action & ~CPU_TASKS_FROZEN) == CPU_STARTING)
+ dummy_setup();
+
+ return NOTIFY_OK;
+}
+
+static struct notifier_block dummy_cpu_nb __cpuinitdata = {
+ .notifier_call = dummy_cpu_notify,
+};
+
+static int __init dummy_register(void)
+{
+ int err = register_cpu_notifier(&dummy_cpu_nb);
+ if (err)
+ return err;
+
+ /* We won't get a call on the boot CPU, so register immediately */
+ dummy_setup();
+
+ return 0;
+}
+device_initcall(dummy_register);
--
1.8.1.1
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