ARM: 7653/2: do not scale loops_per_jiffy when using a constant delay clock (70264367) · Commits · 戴 / test

When udelay() is implemented using an architected timer, it is wrong to scale loops_per_jiffy when changing the CPU clock frequency since the timer clock remains constant. The lpj should probably become an implementation detail relevant to the CPU loop based delay routine only and more confined to it. In the mean time this is the minimal fix needed to have expected delays with the timer based implementation when cpufreq is also in use. Reported-by:

Viresh Kumar <viresh.kumar@linaro.org> Signed-off-by:

Nicolas Pitre <nico@linaro.org> Tested-by:

Viresh Kumar <viresh.kumar@linaro.org> Acked-by:

Liviu Dudau <Liviu.Dudau@arm.com> Cc: stable@vger.kernel.org Signed-off-by:

Russell King <rmk+kernel@arm.linux.org.uk>

arch/arm/include/asm/delay.h

+1 −0

Original line number	Diff line number	Diff line
		@@ -24,6 +24,7 @@ extern struct arm_delay_ops {
		void (*delay)(unsigned long);
		void (*const_udelay)(unsigned long);
		void (*udelay)(unsigned long);
		bool const_clock;
		} arm_delay_ops;

		#define __delay(n) arm_delay_ops.delay(n)

arch/arm/kernel/smp.c

+3 −0

Original line number	Diff line number	Diff line
		@@ -693,6 +693,9 @@ 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

+1 −0

Original line number	Diff line number	Diff line
		@@ -77,6 +77,7 @@ void __init register_current_timer_delay(const struct delay_timer *timer)
		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");

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