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Subject[PATCH] ARM: smp_twd: Reconfigure clockevents after cpufreq change
Date
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.

Signed-off-by: Colin Cross <ccross@android.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Russell King <linux@arm.linux.org.uk>
Cc: Santosh Shilimkar <santosh.shilimkar@ti.com>
Cc: Rob Herring <robherring2@gmail.com>
---
arch/arm/kernel/smp_twd.c | 69 +++++++++++++++++++++++++++++++++++++++++++--
1 files changed, 66 insertions(+), 3 deletions(-)
This patch depends on Thomas Gleixner's patch to add clockevents_reconfigure
See: https://lkml.org/lkml/2011/5/13/122

This patch adds a clock that can be used to skip calibration as well
as update the frequency. A later patch (or a later version of this patch)
will drop twd_calibrate_rate once all platforms provide the necessary
smp_twd clock.

diff --git a/arch/arm/kernel/smp_twd.c b/arch/arm/kernel/smp_twd.c
index 60636f4..dbf58d4 100644
--- a/arch/arm/kernel/smp_twd.c
+++ b/arch/arm/kernel/smp_twd.c
@@ -10,21 +10,29 @@
*/
#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>

+#define TWD_MIN_RANGE 4
+
/* 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 +88,49 @@ int twd_timer_ack(void)
return 0;
}

+/*
+ * 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_reconfigure(__get_cpu_var(twd_ce), twd_timer_rate,
+ TWD_MIN_RANGE);
+}
+
+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);
+
static void __cpuinit twd_calibrate_rate(void)
{
unsigned long count;
@@ -124,7 +175,16 @@ static void __cpuinit twd_calibrate_rate(void)
*/
void __cpuinit twd_timer_setup(struct clock_event_device *clk)
{
- twd_calibrate_rate();
+ if (twd_clk == NULL) {
+ twd_clk = clk_get_sys("smp_twd", NULL);
+ if (IS_ERR_OR_NULL(twd_clk))
+ pr_warn("%s: no clock found\n", __func__);
+ }
+
+ 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 +192,16 @@ 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);
+
+ clockevents_calc_mult_shift(clk, twd_timer_rate, TWD_MIN_RANGE);
+
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);

+ __get_cpu_var(twd_ce) = clk;
+
clockevents_register_device(clk);
}
--
1.7.4.1


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