From 128f79c82dccb1ac9eacf8fa0b4d52bb29e05278 Mon Sep 17 00:00:00 2001
From: Colin Cross <ccross@google.com>
Date: Thu, 19 Aug 2010 22:07:43 -0700
Subject: [PATCH] [ARM] twd: Allow twd rescaling to match cpu frequency
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 relation between the cpu
clock and the TWD clock, required to be an integer divider
>= 2 by the ARM spec. It also provides a function to be
called from cpufreq drivers to set the prescaler whenever
the cpu frequency changes.
Also fixes a typo in the printk of the calibrated frequency.
Change-Id: I3fa8ef718ff5518170f1b2bab29efe960741853e
Signed-off-by: Colin Cross <ccross@google.com>
---
arch/arm/include/asm/smp_twd.h | 19 ++++++++++++
arch/arm/kernel/smp_twd.c | 57 +++++++++++++++++++++++++++++++---
2 files changed, 72 insertions(+), 4 deletions(-)
diff --git a/arch/arm/include/asm/smp_twd.h b/arch/arm/include/asm/smp_twd.h
index 634f357be6bb..79aebe2ad7a8 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 +27,22 @@ void twd_timer_stop(void);
int twd_timer_ack(void);
void twd_timer_setup(struct clock_event_device *);
+/*
+ * Use this setup function on systems where the cpu clock frequency may
+ * change. 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.
+ */
+void twd_timer_setup_scalable(struct clock_event_device *,
+ unsigned long target_rate, unsigned int periphclk_prescaler);
+
+/*
+ * Recalculate the twd prescaler value when the cpu frequency changes. To
+ * prevent early timer interrupts, must be called before changing the cpu
+ * frequency if the frequency is increasing, or after if the frequency is
+ * decreasing.
+ */
+void twd_recalc_prescaler(unsigned long new_rate);
+
#endif
diff --git a/arch/arm/kernel/smp_twd.c b/arch/arm/kernel/smp_twd.c
index 35882fbf37f9..2b4f92788c0e 100644
--- a/arch/arm/kernel/smp_twd.c
+++ b/arch/arm/kernel/smp_twd.c
@@ -25,6 +25,8 @@
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)
@@ -79,10 +81,31 @@ int twd_timer_ack(void)
return 0;
}
-static void __cpuinit twd_calibrate_rate(void)
+void twd_recalc_prescaler(unsigned long new_rate)
+{
+ u32 ctrl;
+ int prescaler;
+ unsigned long periphclk_rate;
+
+ BUG_ON(twd_periphclk_prescaler == 0 || twd_timer_rate == 0);
+
+ periphclk_rate = new_rate / twd_periphclk_prescaler;
+
+ prescaler = DIV_ROUND_UP(periphclk_rate, twd_timer_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 __cpuinit twd_calibrate_rate(unsigned long target_rate,
+ unsigned int periphclk_prescaler)
{
unsigned long load, count;
u64 waitjiffies;
+ unsigned long cpu_rate;
/*
* If this is the first time round, we need to work out how fast
@@ -113,8 +136,22 @@ static void __cpuinit twd_calibrate_rate(void)
twd_timer_rate = (0xFFFFFFFFU - count) * (HZ / 5);
+ /*
+ * If a target rate has been requested, adjust the TWD prescaler
+ * to get the closest lower frequency.
+ */
+ if (target_rate) {
+ twd_periphclk_prescaler = periphclk_prescaler;
+ twd_target_rate = target_rate;
+
+ cpu_rate = twd_timer_rate * periphclk_prescaler;
+ twd_recalc_prescaler(cpu_rate);
+
+ twd_timer_rate = twd_target_rate;
+ }
+
printk("%lu.%02luMHz.\n", twd_timer_rate / 1000000,
- (twd_timer_rate / 100000) % 100);
+ (twd_timer_rate / 10000) % 100);
}
load = twd_timer_rate / HZ;
@@ -125,11 +162,12 @@ static void __cpuinit twd_calibrate_rate(void)
/*
* 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;
- twd_calibrate_rate();
+ twd_calibrate_rate(target_rate, periphclk_prescaler);
clk->name = "local_timer";
clk->features = CLOCK_EVT_FEAT_PERIODIC | CLOCK_EVT_FEAT_ONESHOT |
@@ -151,6 +189,17 @@ 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);
+}
+
#ifdef CONFIG_HOTPLUG_CPU
/*
* take a local timer down
--
2.34.1