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Message-Id: <1290060899-9786-1-git-send-email-ccross@android.com>
Date: Wed, 17 Nov 2010 22:14:59 -0800
From: Colin Cross <ccross@...roid.com>
To: linux-arm-kernel@...ts-infradead.org
Cc: Harald Gustafsson <harald.gustafsson@...csson.com>,
Rickard ANDERSSON <Rickard.Andersson@...ricsson.com>,
Rob Herring <robherring2@...il.com>,
Colin Cross <ccross@...roid.com>,
Russell King <linux@....linux.org.uk>,
srinidhi kasagar <srinidhi.kasagar@...ricsson.com>,
Linus Walleij <linus.walleij@...ricsson.com>,
Varun Swara <Varun.Swara@....com>,
Catalin Marinas <catalin.marinas@....com>,
linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: [PATCH] ARM: twd: Adjust localtimer frequency with cpufreq notifiers
The clock to the ARM TWD local timer scales with the cpu
frequency. To allow the cpu frequency to change while
maintaining a constant TWD frequency, pick a lower target
frequency for the TWD and use the prescaler to divide down
to the closest lower frequency.
This patch provides a new initialization function that takes
a target TWD frequency and the ratio between the cpu
clock and the TWD clock, specified as an integer divider >= 2
in the Cortex A9 MPCore TRM, and 2 in the ARM11 MPCore TRM.
It also registers a cpufreq notifier that adjusts the
prescaler when the cpu frequency changes.
Signed-off-by: Colin Cross <ccross@...roid.com>
---
arch/arm/include/asm/smp_twd.h | 11 ++++
arch/arm/kernel/smp_twd.c | 106 +++++++++++++++++++++++++++++++++++++---
2 files changed, 109 insertions(+), 8 deletions(-)
diff --git a/arch/arm/include/asm/smp_twd.h b/arch/arm/include/asm/smp_twd.h
index 634f357..5119763 100644
--- a/arch/arm/include/asm/smp_twd.h
+++ b/arch/arm/include/asm/smp_twd.h
@@ -17,6 +17,7 @@
#define TWD_TIMER_CONTROL_ONESHOT (0 << 1)
#define TWD_TIMER_CONTROL_PERIODIC (1 << 1)
#define TWD_TIMER_CONTROL_IT_ENABLE (1 << 2)
+#define TWD_TIMER_CONTROL_PRESCALE_MASK (0xFF << 8)
struct clock_event_device;
@@ -26,4 +27,14 @@ void twd_timer_stop(void);
int twd_timer_ack(void);
void twd_timer_setup(struct clock_event_device *);
+/*
+ * Use this setup function on systems that support cpufreq.
+ * periphclk_prescaler is the fixed divider value between the cpu
+ * clock and the PERIPHCLK clock that feeds the TWD. target_rate should be
+ * low enough that the prescaler can accurately reach the target rate from the
+ * lowest cpu frequency, but high enough to give a reasonable timer accuracy.
+ */
+void twd_timer_setup_scalable(struct clock_event_device *,
+ unsigned long target_rate, unsigned int periphclk_prescaler);
+
#endif
diff --git a/arch/arm/kernel/smp_twd.c b/arch/arm/kernel/smp_twd.c
index 35882fb..e2bc65c 100644
--- a/arch/arm/kernel/smp_twd.c
+++ b/arch/arm/kernel/smp_twd.c
@@ -17,6 +17,7 @@
#include <linux/clockchips.h>
#include <linux/irq.h>
#include <linux/io.h>
+#include <linux/cpufreq.h>
#include <asm/smp_twd.h>
#include <asm/hardware/gic.h>
@@ -25,11 +26,17 @@
void __iomem *twd_base;
static unsigned long twd_timer_rate;
+static unsigned long twd_periphclk_prescaler;
+static unsigned long twd_target_rate;
static void twd_set_mode(enum clock_event_mode mode,
struct clock_event_device *clk)
{
unsigned long ctrl;
+ unsigned long prescale;
+
+ prescale = __raw_readl(twd_base + TWD_TIMER_CONTROL) &
+ TWD_TIMER_CONTROL_PRESCALE_MASK;
switch (mode) {
case CLOCK_EVT_MODE_PERIODIC:
@@ -47,6 +54,8 @@ static void twd_set_mode(enum clock_event_mode mode,
ctrl = 0;
}
+ ctrl |= prescale;
+
__raw_writel(ctrl, twd_base + TWD_TIMER_CONTROL);
}
@@ -79,9 +88,55 @@ int twd_timer_ack(void)
return 0;
}
+/*
+ * must be called with interrupts disabled and on the cpu that is being changed
+ */
+static void twd_update_cpu_frequency(unsigned long new_rate)
+{
+ u32 ctrl;
+ int prescaler;
+
+ BUG_ON(twd_periphclk_prescaler == 0 || twd_target_rate == 0);
+
+ twd_timer_rate = new_rate / twd_periphclk_prescaler;
+
+ prescaler = DIV_ROUND_UP(twd_timer_rate, twd_target_rate);
+ prescaler = clamp(prescaler - 1, 0, 0xFF);
+
+ ctrl = __raw_readl(twd_base + TWD_TIMER_CONTROL);
+ ctrl &= ~TWD_TIMER_CONTROL_PRESCALE_MASK;
+ ctrl |= prescaler << 8;
+ __raw_writel(ctrl, twd_base + TWD_TIMER_CONTROL);
+}
+
+static void twd_update_cpu_frequency_on_cpu(void *data)
+{
+ struct cpufreq_freqs *freq = data;
+
+ twd_update_cpu_frequency(freq->new * 1000);
+}
+
+static int twd_cpufreq_notifier(struct notifier_block *nb,
+ unsigned long event, void *data)
+{
+ struct cpufreq_freqs *freq = data;
+
+ if (event == CPUFREQ_RESUMECHANGE ||
+ (event == CPUFREQ_PRECHANGE && freq->new > freq->old) ||
+ (event == CPUFREQ_POSTCHANGE && freq->new < freq->old))
+ smp_call_function_single(freq->cpu,
+ twd_update_cpu_frequency_on_cpu, freq, 1);
+
+ return 0;
+}
+
+static struct notifier_block twd_cpufreq_notifier_block = {
+ .notifier_call = twd_cpufreq_notifier,
+};
+
static void __cpuinit twd_calibrate_rate(void)
{
- unsigned long load, count;
+ unsigned long count;
u64 waitjiffies;
/*
@@ -114,23 +169,37 @@ static void __cpuinit twd_calibrate_rate(void)
twd_timer_rate = (0xFFFFFFFFU - count) * (HZ / 5);
printk("%lu.%02luMHz.\n", twd_timer_rate / 1000000,
- (twd_timer_rate / 100000) % 100);
+ (twd_timer_rate / 10000) % 100);
}
-
- load = twd_timer_rate / HZ;
-
- __raw_writel(load, twd_base + TWD_TIMER_LOAD);
}
/*
* Setup the local clock events for a CPU.
*/
-void __cpuinit twd_timer_setup(struct clock_event_device *clk)
+static void __cpuinit __twd_timer_setup(struct clock_event_device *clk,
+ unsigned long target_rate, unsigned int periphclk_prescaler)
{
unsigned long flags;
+ unsigned long load;
+ unsigned long cpu_rate;
+ unsigned long twd_tick_rate;
twd_calibrate_rate();
+ if (target_rate && periphclk_prescaler) {
+ cpu_rate = twd_timer_rate * periphclk_prescaler;
+ twd_target_rate = target_rate;
+ twd_periphclk_prescaler = periphclk_prescaler;
+ twd_update_cpu_frequency(cpu_rate);
+ twd_tick_rate = twd_target_rate;
+ } else {
+ twd_tick_rate = twd_timer_rate;
+ }
+
+ load = twd_tick_rate / HZ;
+
+ __raw_writel(load, twd_base + TWD_TIMER_LOAD);
+
clk->name = "local_timer";
clk->features = CLOCK_EVT_FEAT_PERIODIC | CLOCK_EVT_FEAT_ONESHOT |
CLOCK_EVT_FEAT_C3STOP;
@@ -138,7 +207,7 @@ void __cpuinit twd_timer_setup(struct clock_event_device *clk)
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->mult = div_sc(twd_tick_rate, NSEC_PER_SEC, clk->shift);
clk->max_delta_ns = clockevent_delta2ns(0xffffffff, clk);
clk->min_delta_ns = clockevent_delta2ns(0xf, clk);
@@ -151,6 +220,27 @@ void __cpuinit twd_timer_setup(struct clock_event_device *clk)
clockevents_register_device(clk);
}
+void __cpuinit twd_timer_setup_scalable(struct clock_event_device *clk,
+ unsigned long target_rate, unsigned int periphclk_prescaler)
+{
+ __twd_timer_setup(clk, target_rate, periphclk_prescaler);
+}
+
+void __cpuinit twd_timer_setup(struct clock_event_device *clk)
+{
+ __twd_timer_setup(clk, 0, 0);
+}
+
+static int twd_timer_setup_cpufreq(void)
+{
+ if (twd_periphclk_prescaler)
+ cpufreq_register_notifier(&twd_cpufreq_notifier_block,
+ CPUFREQ_TRANSITION_NOTIFIER);
+
+ return 0;
+}
+arch_initcall(twd_timer_setup_cpufreq);
+
#ifdef CONFIG_HOTPLUG_CPU
/*
* take a local timer down
--
1.7.3.1
--
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