ARM: 7685/1: delay: use private ticks_per_jiffy field for timer-based…

… delay ops

Commit 7026436 ("ARM: 7653/2: do not scale loops_per_jiffy when
using a constant delay clock") fixed a problem with our timer-based
delay loop, where loops_per_jiffy is scaled by cpufreq yet used directly
by the timer delay ops.

This patch fixes the problem in a more elegant way by keeping a private
ticks_per_jiffy field in the delay ops, independent of loops_per_jiffy
and therefore not subject to scaling. The loop-based delay continues to
use loops_per_jiffy directly, as it should.

Acked-by: Nicolas Pitre <nico@linaro.org>
Signed-off-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>

arch/arm/include/asm/delay.h

@@ -24,7 +24,7 @@ extern struct arm_delay_ops {
 	void (*delay)(unsigned long);
 	void (*const_udelay)(unsigned long);
 	void (*udelay)(unsigned long);
-	bool const_clock;
+	unsigned long ticks_per_jiffy;
 } arm_delay_ops;
 
 #define __delay(n)		arm_delay_ops.delay(n)

arch/arm/kernel/smp.c

@@ -673,9 +673,6 @@ static int cpufreq_callback(struct notifier_block *nb,
 	if (freq->flags & CPUFREQ_CONST_LOOPS)
 		return NOTIFY_OK;
 
-	if (arm_delay_ops.const_clock)
-		return NOTIFY_OK;
-
 	if (!per_cpu(l_p_j_ref, cpu)) {
 		per_cpu(l_p_j_ref, cpu) =
 			per_cpu(cpu_data, cpu).loops_per_jiffy;

arch/arm/lib/delay.c

@@ -58,7 +58,7 @@ static void __timer_delay(unsigned long cycles)
 static void __timer_const_udelay(unsigned long xloops)
 {
 	unsigned long long loops = xloops;
-	loops *= loops_per_jiffy;
+	loops *= arm_delay_ops.ticks_per_jiffy;
 	__timer_delay(loops >> UDELAY_SHIFT);
 }
 
@@ -73,11 +73,13 @@ void __init register_current_timer_delay(const struct delay_timer *timer)
 		pr_info("Switching to timer-based delay loop\n");
 		delay_timer			= timer;
 		lpj_fine			= timer->freq / HZ;
-		loops_per_jiffy			= lpj_fine;
+
+		/* cpufreq may scale loops_per_jiffy, so keep a private copy */
+		arm_delay_ops.ticks_per_jiffy	= lpj_fine;
 		arm_delay_ops.delay		= __timer_delay;
 		arm_delay_ops.const_udelay	= __timer_const_udelay;
 		arm_delay_ops.udelay		= __timer_udelay;
-		arm_delay_ops.const_clock	= true;
+
 		delay_calibrated		= true;
 	} else {
 		pr_info("Ignoring duplicate/late registration of read_current_timer delay\n");