[PATCH RESEND] ARM: smp_twd: Reconfigure clockevents after cpufreq change

[PATCH RESEND] ARM: smp_twd: Reconfigure clockevents after cpufreq change

[Linus Walleij]

From: Colin Cross <ccross@android.com>

The localtimer's clock changes with the cpu clock. After a
cpufreq transition, update the clockevent's frequency and
reprogram the next clock event.

Adds a clock called "smp_twd" that is used to determine the
twd frequency, which can also be used at init time to
avoid calibrating the twd frequency.

Clock changes are based on Rob Herring's work. The
necessary changes in the clockevents framework was done by
Thomas Gleixner in kernel v3.0.

Signed-off-by: Colin Cross <ccross@android.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Russell King <linux@arm.linux.org.uk>
Acked-by: Rob Herring <rob.herring@calxeda.com>
Acked-by: Santosh Shilimkar <santosh.shilimkar@ti.com>
[ifdef:ed CPUfreq stuff for non-cpufreq configs]
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
---
Any further comments on this? It solves a real issue for
ST-Ericsson Ux500, nVidia Tegra and ARM Versatile Express.

Infrastructural changes required in clockchips.h were merged
by tglx in kernel v3.0.

Rob: if you think this is good could you please retire
patch 6802/1 to lower the fuzz around this?

Thanks,
Linus Walleij

 arch/arm/kernel/smp_twd.c |   90 ++++++++++++++++++++++++++++++++++++++++++---
 1 files changed, 84 insertions(+), 6 deletions(-)

diff --git a/arch/arm/kernel/smp_twd.c b/arch/arm/kernel/smp_twd.c
index 2c277d4..36c12ef 100644
--- a/arch/arm/kernel/smp_twd.c
+++ b/arch/arm/kernel/smp_twd.c
@@ -10,13 +10,17 @@
  */
 #include <linux/init.h>
 #include <linux/kernel.h>
+#include <linux/clk.h>
+#include <linux/cpufreq.h>
 #include <linux/delay.h>
 #include <linux/device.h>
+#include <linux/err.h>
 #include <linux/smp.h>
 #include <linux/jiffies.h>
 #include <linux/clockchips.h>
 #include <linux/irq.h>
 #include <linux/io.h>
+#include <linux/percpu.h>
 
 #include <asm/smp_twd.h>
 #include <asm/hardware/gic.h>
@@ -24,7 +28,9 @@
 /* set up by the platform code */
 void __iomem *twd_base;
 
+static struct clk *twd_clk;
 static unsigned long twd_timer_rate;
+static DEFINE_PER_CPU(struct clock_event_device *, twd_ce);
 
 static void twd_set_mode(enum clock_event_mode mode,
 			struct clock_event_device *clk)
@@ -80,6 +86,52 @@ int twd_timer_ack(void)
 	return 0;
 }
 
+#ifdef CONFIG_CPU_FREQ
+
+/*
+ * Updates clockevent frequency when the cpu frequency changes.
+ * Called on the cpu that is changing frequency with interrupts disabled.
+ */
+static void twd_update_frequency(void *data)
+{
+	twd_timer_rate = clk_get_rate(twd_clk);
+
+	clockevents_update_freq(__get_cpu_var(twd_ce), twd_timer_rate);
+}
+
+static int twd_cpufreq_transition(struct notifier_block *nb,
+	unsigned long state, void *data)
+{
+	struct cpufreq_freqs *freqs = data;
+
+	/*
+	 * The twd clock events must be reprogrammed to account for the new
+	 * frequency.  The timer is local to a cpu, so cross-call to the
+	 * changing cpu.
+	 */
+	if (state == CPUFREQ_POSTCHANGE || state == CPUFREQ_RESUMECHANGE)
+		smp_call_function_single(freqs->cpu, twd_update_frequency,
+			NULL, 1);
+
+	return NOTIFY_OK;
+}
+
+static struct notifier_block twd_cpufreq_nb = {
+	.notifier_call = twd_cpufreq_transition,
+};
+
+static int twd_cpufreq_init(void)
+{
+	if (!IS_ERR_OR_NULL(twd_clk))
+		return cpufreq_register_notifier(&twd_cpufreq_nb,
+			CPUFREQ_TRANSITION_NOTIFIER);
+
+	return 0;
+}
+core_initcall(twd_cpufreq_init);
+
+#endif
+
 static void __cpuinit twd_calibrate_rate(void)
 {
 	unsigned long count;
@@ -119,12 +171,39 @@ static void __cpuinit twd_calibrate_rate(void)
 	}
 }
 
+static struct clk *twd_get_clock(void)
+{
+	struct clk *clk;
+	int err;
+
+	clk = clk_get_sys("smp_twd", NULL);
+	if (IS_ERR(clk)) {
+		pr_err("smp_twd: clock not found: %d\n", (int)PTR_ERR(clk));
+		return clk;
+	}
+
+	err = clk_enable(clk);
+	if (err) {
+		pr_err("smp_twd: clock failed to enable: %d\n", err);
+		clk_put(clk);
+		return ERR_PTR(err);
+	}
+
+	return clk;
+}
+
 /*
  * Setup the local clock events for a CPU.
  */
 void __cpuinit twd_timer_setup(struct clock_event_device *clk)
 {
-	twd_calibrate_rate();
+	if (!twd_clk)
+		twd_clk = twd_get_clock();
+
+	if (!IS_ERR_OR_NULL(twd_clk))
+		twd_timer_rate = clk_get_rate(twd_clk);
+	else
+		twd_calibrate_rate();
 
 	clk->name = "local_timer";
 	clk->features = CLOCK_EVT_FEAT_PERIODIC | CLOCK_EVT_FEAT_ONESHOT |
@@ -132,13 +211,12 @@ void __cpuinit twd_timer_setup(struct clock_event_device *clk)
 	clk->rating = 350;
 	clk->set_mode = twd_set_mode;
 	clk->set_next_event = twd_set_next_event;
-	clk->shift = 20;
-	clk->mult = div_sc(twd_timer_rate, NSEC_PER_SEC, clk->shift);
-	clk->max_delta_ns = clockevent_delta2ns(0xffffffff, clk);
-	clk->min_delta_ns = clockevent_delta2ns(0xf, clk);
 
 	/* Make sure our local interrupt controller has this enabled */
 	gic_enable_ppi(clk->irq);
 
-	clockevents_register_device(clk);
+	__get_cpu_var(twd_ce) = clk;
+
+	clockevents_config_and_register(clk, twd_timer_rate,
+					0xf, 0xffffffff);
 }
-- 
1.7.3.2

[PATCH RESEND] ARM: smp_twd: Reconfigure clockevents after cpufreq change

[Linus Walleij]

2011/9/6 Linus Walleij <linus.walleij@stericsson.com>:

> From: Colin Cross <ccross@android.com>
>
> The localtimer's clock changes with the cpu clock. After a
> cpufreq transition, update the clockevent's frequency and
> reprogram the next clock event.

Thomas do you think you can have a look at this patch and ACK
it if it looks OK to you? It's the use of clockevents_update_freq()
function you added after we discussed this in Budapest.

Since it's likely the first user of that infrastructure we need
to get it right.

Here is the entire patch i Russells tracker:
http://www.arm.linux.org.uk/developer/patches/viewpatch.php?id=6956/2

Tell me if you want me to resend the patch again and
I'll fix.

Yours,
Linus Walleij

[PATCH RESEND] ARM: smp_twd: Reconfigure clockevents after cpufreq change

[Thomas Gleixner]

On Thu, 6 Oct 2011, Linus Walleij wrote:

> 2011/9/6 Linus Walleij <linus.walleij@stericsson.com>:
> 
> > From: Colin Cross <ccross@android.com>
> >
> > The localtimer's clock changes with the cpu clock. After a
> > cpufreq transition, update the clockevent's frequency and
> > reprogram the next clock event.
> 
> Thomas do you think you can have a look at this patch and ACK
> it if it looks OK to you? It's the use of clockevents_update_freq()
> function you added after we discussed this in Budapest.
> 
> Since it's likely the first user of that infrastructure we need
> to get it right.

The usage is correct.
 
> Here is the entire patch i Russells tracker:
> http://www.arm.linux.org.uk/developer/patches/viewpatch.php?id=6956/2

The only thing what puzzles me is:

> +	if (!IS_ERR_OR_NULL(twd_clk))
> +		twd_timer_rate = clk_get_rate(twd_clk);
> +	else
> +		twd_calibrate_rate();

How is made sure that the cpu freq update thing is not called when
twd_clk is not available or am I missing something ?

Thanks,

	tglx

[PATCH RESEND] ARM: smp_twd: Reconfigure clockevents after cpufreq change

[Linus Walleij]

On Thu, Oct 6, 2011 at 7:25 PM, Thomas Gleixner <tglx@linutronix.de> wrote:
> On Thu, 6 Oct 2011, Linus Walleij wrote:
>> Here is the entire patch i Russells tracker:
>> http://www.arm.linux.org.uk/developer/patches/viewpatch.php?id=6956/2
>
> The only thing what puzzles me is:
>
>> + ? ? if (!IS_ERR_OR_NULL(twd_clk))
>> + ? ? ? ? ? ? twd_timer_rate = clk_get_rate(twd_clk);
>> + ? ? else
>> + ? ? ? ? ? ? twd_calibrate_rate();
>
> How is made sure that the cpu freq update thing is not called when
> twd_clk is not available or am I missing something ?

The CPUfreq transition notifier is only registered if twd_clk is
not error or NULL in this #ifdef CONFIG_CPU_FREQ snippet
above that code, but executed later:

+static int twd_cpufreq_init(void)
+{
+	if (!IS_ERR_OR_NULL(twd_clk))
+		return cpufreq_register_notifier(&twd_cpufreq_nb,
+			CPUFREQ_TRANSITION_NOTIFIER);
+
+	return 0;
+}
+core_initcall(twd_cpufreq_init);

Yours,
Linus Walleij

[PATCH RESEND] ARM: smp_twd: Reconfigure clockevents after cpufreq change

[Thomas Gleixner]

On Fri, 7 Oct 2011, Linus Walleij wrote:

> On Thu, Oct 6, 2011 at 7:25 PM, Thomas Gleixner <tglx@linutronix.de> wrote:
> > On Thu, 6 Oct 2011, Linus Walleij wrote:
> >> Here is the entire patch i Russells tracker:
> >> http://www.arm.linux.org.uk/developer/patches/viewpatch.php?id=6956/2
> >
> > The only thing what puzzles me is:
> >
> >> + ? ? if (!IS_ERR_OR_NULL(twd_clk))
> >> + ? ? ? ? ? ? twd_timer_rate = clk_get_rate(twd_clk);
> >> + ? ? else
> >> + ? ? ? ? ? ? twd_calibrate_rate();
> >
> > How is made sure that the cpu freq update thing is not called when
> > twd_clk is not available or am I missing something ?
> 
> The CPUfreq transition notifier is only registered if twd_clk is
> not error or NULL in this #ifdef CONFIG_CPU_FREQ snippet
> above that code, but executed later:
> 
> +static int twd_cpufreq_init(void)
> +{
> +	if (!IS_ERR_OR_NULL(twd_clk))
> +		return cpufreq_register_notifier(&twd_cpufreq_nb,
> +			CPUFREQ_TRANSITION_NOTIFIER);
> +
> +	return 0;
> +}
> +core_initcall(twd_cpufreq_init);

Duh. Could have seen that myself :)

Thans for clarification. Please add my Acked-by.

Thanks,

	tglx