[PATCH v2 2/2] ARM: delay: allow timer-based delay implementation to be selected
Will Deacon
will.deacon at arm.com
Wed Jul 18 13:52:33 EDT 2012
Hello,
On Tue, Jul 17, 2012 at 08:42:36AM +0100, Shinya Kuribayashi wrote:
> On 7/17/2012 3:11 PM, Shilimkar, Santosh wrote:
> > Looks like you have a working patch for the clock detection. Will
> > you able to post that patch so that this long pending calibration
> > for secondary CPUs gets optimized.
>
> Something like this should work (not even build tested, can be applied
> on top of Will's v2 patchset):
[...]
> And change your ->timer() func (called via time_init) to make use of it:
>
> unsigned long freq;
>
> /* For UP/SMP systems */
> freq = get_CPU_frequency();
> calibrate_delay_early(freq);
>
> #ifdef CONFIG_SMP
> /* For SMP systems */
> freq = get_Timer_frequency();
> init_current_timer_delay(freq);
> #endif
Since this seems to be gaining some traction on platforms without the
architected timers, Jonny and I have put together a simple registration
mechanism for the delay timer to avoid people calling init_current_timer_delay
(and defining the global read_current_timer symbol).
The patch is sitting in my delay branch, but I've also included it below.
Please give it a go and let us know what you think.
Cheers,
Will
---8<---
>From 8ea28b6f7acad17b9952f8eb533f2887504b462d Mon Sep 17 00:00:00 2001
From: Jonathan Austin <Jonathan.Austin at arm.com>
Date: Wed, 18 Jul 2012 15:24:53 +0100
Subject: [PATCH] ARM: delay: add registration mechanism for delay timer sources
The current timer-based delay loop relies on the architected timer to
initiate the switch away from the polling-based implementation. This is
unfortunate for platforms without the architected timers but with a
suitable delay source (that is, constant frequency, always powered-up
and ticking as long as the CPUs are online).
This patch introduces a registration mechanism for the delay timer
(which provides an unconditional read_current_timer implementation) and
updates the architected timer code to use the new interface.
Signed-off-by: Jonathan Austin <jonathan.austin at arm.com>
Signed-off-by: Will Deacon <will.deacon at arm.com>
---
arch/arm/include/asm/arch_timer.h | 1 -
arch/arm/include/asm/delay.h | 9 +++++++++
arch/arm/include/asm/timex.h | 6 ------
arch/arm/kernel/arch_timer.c | 12 +++++++-----
arch/arm/lib/delay.c | 30 +++++++++++++++++++++---------
5 files changed, 37 insertions(+), 21 deletions(-)
diff --git a/arch/arm/include/asm/arch_timer.h b/arch/arm/include/asm/arch_timer.h
index 62e7547..88401c2 100644
--- a/arch/arm/include/asm/arch_timer.h
+++ b/arch/arm/include/asm/arch_timer.h
@@ -4,7 +4,6 @@
#include <asm/errno.h>
#ifdef CONFIG_ARM_ARCH_TIMER
-#define ARCH_HAS_READ_CURRENT_TIMER
int arch_timer_of_register(void);
int arch_timer_sched_clock_init(void);
#else
diff --git a/arch/arm/include/asm/delay.h b/arch/arm/include/asm/delay.h
index dc61451..17deac7 100644
--- a/arch/arm/include/asm/delay.h
+++ b/arch/arm/include/asm/delay.h
@@ -15,6 +15,11 @@
#ifndef __ASSEMBLY__
+struct delay_timer {
+ int (*read_current_timer)(unsigned long *timer_val);
+ unsigned long freq;
+};
+
extern struct arm_delay_ops {
void (*delay)(unsigned long);
void (*const_udelay)(unsigned long);
@@ -56,6 +61,10 @@ extern void __loop_delay(unsigned long loops);
extern void __loop_udelay(unsigned long usecs);
extern void __loop_const_udelay(unsigned long);
+/* Delay-loop timer registration. */
+#define ARCH_HAS_READ_CURRENT_TIMER
+extern void register_current_timer_delay(struct delay_timer *timer);
+
#endif /* __ASSEMBLY__ */
#endif /* defined(_ARM_DELAY_H) */
diff --git a/arch/arm/include/asm/timex.h b/arch/arm/include/asm/timex.h
index ce11944..9acc135 100644
--- a/arch/arm/include/asm/timex.h
+++ b/arch/arm/include/asm/timex.h
@@ -12,15 +12,9 @@
#ifndef _ASMARM_TIMEX_H
#define _ASMARM_TIMEX_H
-#include <asm/arch_timer.h>
#include <mach/timex.h>
typedef unsigned long cycles_t;
-
-#ifdef ARCH_HAS_READ_CURRENT_TIMER
#define get_cycles() ({ cycles_t c; read_current_timer(&c) ? 0 : c; })
-#else
-#define get_cycles() (0)
-#endif
#endif
diff --git a/arch/arm/kernel/arch_timer.c b/arch/arm/kernel/arch_timer.c
index 675cee0..b624523 100644
--- a/arch/arm/kernel/arch_timer.c
+++ b/arch/arm/kernel/arch_timer.c
@@ -21,6 +21,7 @@
#include <linux/io.h>
#include <asm/cputype.h>
+#include <asm/delay.h>
#include <asm/localtimer.h>
#include <asm/arch_timer.h>
#include <asm/system_info.h>
@@ -31,8 +32,7 @@ static int arch_timer_ppi;
static int arch_timer_ppi2;
static struct clock_event_device __percpu **arch_timer_evt;
-
-extern void init_current_timer_delay(unsigned long freq);
+static struct delay_timer arch_delay_timer;
/*
* Architected system timer support.
@@ -225,7 +225,7 @@ static cycle_t arch_counter_read(struct clocksource *cs)
return arch_counter_get_cntpct();
}
-int read_current_timer(unsigned long *timer_val)
+static int arch_timer_read_current_timer(unsigned long *timer_val)
{
if (!arch_timer_rate)
return -ENXIO;
@@ -302,11 +302,13 @@ static int __init arch_timer_register(void)
arch_timer_global_evt.cpumask = cpumask_of(0);
err = arch_timer_setup(&arch_timer_global_evt);
}
-
if (err)
goto out_free_irq;
- init_current_timer_delay(arch_timer_rate);
+ /* Use the architected timer for the delay loop. */
+ arch_delay_timer.read_current_timer = &arch_timer_read_current_timer;
+ arch_delay_timer.freq = arch_timer_rate;
+ register_current_timer_delay(&arch_delay_timer);
return 0;
out_free_irq:
diff --git a/arch/arm/lib/delay.c b/arch/arm/lib/delay.c
index 395d5fb..1b51570 100644
--- a/arch/arm/lib/delay.c
+++ b/arch/arm/lib/delay.c
@@ -34,7 +34,14 @@ struct arm_delay_ops arm_delay_ops = {
.udelay = __loop_udelay,
};
-#ifdef ARCH_HAS_READ_CURRENT_TIMER
+static struct delay_timer *delay_timer;
+static bool delay_calibrated;
+
+int read_current_timer(unsigned long *timer_val)
+{
+ return delay_timer ? delay_timer->read_current_timer(timer_val) : -ENXIO;
+}
+
static void __timer_delay(unsigned long cycles)
{
cycles_t start = get_cycles();
@@ -55,18 +62,23 @@ static void __timer_udelay(unsigned long usecs)
__timer_const_udelay(usecs * UDELAY_MULT);
}
-void __init init_current_timer_delay(unsigned long freq)
+void __init register_current_timer_delay(struct delay_timer *timer)
{
- pr_info("Switching to timer-based delay loop\n");
- lpj_fine = freq / HZ;
- loops_per_jiffy = lpj_fine;
- arm_delay_ops.delay = __timer_delay;
- arm_delay_ops.const_udelay = __timer_const_udelay;
- arm_delay_ops.udelay = __timer_udelay;
+ if (!delay_calibrated) {
+ pr_info("Switching to timer-based delay loop\n");
+ delay_timer = timer;
+ lpj_fine = timer->freq / HZ;
+ loops_per_jiffy = lpj_fine;
+ arm_delay_ops.delay = __timer_delay;
+ arm_delay_ops.const_udelay = __timer_const_udelay;
+ arm_delay_ops.udelay = __timer_udelay;
+ } else {
+ pr_info("Ignoring late registration of read_current_timer delay\n");
+ }
}
unsigned long __cpuinit calibrate_delay_is_known(void)
{
+ delay_calibrated = true;
return lpj_fine;
}
-#endif
--
1.7.4.1
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