ARM: 7563/1: SMP_TWD: make setup()/stop() reentrant (a68becd1) · Commits · 戴 / test

It has been brought to my knowledge that the .setup()/.stop() function pair in the SMP TWD is going to be called from atomic contexts for CPUs coming and going, and then the clk_prepare()/clk_unprepare() calls cannot be called on subsequent .setup()/.stop() iterations. This is however just the tip of an iceberg as the function pair is not designed to be reentrant at all. This change makes the SMP_TWD clock .setup()/.stop() pair reentrant by splitting the .setup() function in three parts: - One COMMON part that is executed the first time the first CPU in the TWD cluster is initialized. This will fetch the TWD clk for the cluster and prepare+enable it. If no clk is available it will calibrate the rate instead. - One part that is executed the FIRST TIME a certain CPU is brought on-line. This initializes and sets up the clock event for a certain CPU. - One part that is executed on every subsequent .setup() call. This will re-initialize the clock event. This is augmented to call the clk_enable()/clk_disable() pair properly. Cc: Shawn Guo <shawn.guo@linaro.org> Reported-by:

Peter Chen <peter.chen@freescale.com> Reviewed-by:

Santosh Shilimkar <santosh.shilimkar@ti.com> Tested-by:

Shawn Guo <shawn.guo@linaro.org> Signed-off-by:

Linus Walleij <linus.walleij@linaro.org> Signed-off-by:

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

arch/arm/kernel/smp_twd.c

+37 −5

Original line number	Diff line number	Diff line
		@@ -31,6 +31,8 @@ static void __iomem *twd_base;

		static struct clk *twd_clk;
		static unsigned long twd_timer_rate;
		static bool common_setup_called;
		static DEFINE_PER_CPU(bool, percpu_setup_called);

		static struct clock_event_device __percpu **twd_evt;
		static int twd_ppi;
		@@ -264,15 +266,45 @@ static struct clk *twd_get_clock(void)
		static int __cpuinit twd_timer_setup(struct clock_event_device *clk)
		{
		struct clock_event_device **this_cpu_clk;
		int cpu = smp_processor_id();

		if (!twd_clk)
		/*
		* If the basic setup for this CPU has been done before don't
		* bother with the below.
		*/
		if (per_cpu(percpu_setup_called, cpu)) {
		__raw_writel(0, twd_base + TWD_TIMER_CONTROL);
		clockevents_register_device(*__this_cpu_ptr(twd_evt));
		enable_percpu_irq(clk->irq, 0);
		return 0;
		}
		per_cpu(percpu_setup_called, cpu) = true;

		/*
		* This stuff only need to be done once for the entire TWD cluster
		* during the runtime of the system.
		*/
		if (!common_setup_called) {
		twd_clk = twd_get_clock();

		/*
		* We use IS_ERR_OR_NULL() here, because if the clock stubs
		* are active we will get a valid clk reference which is
		* however NULL and will return the rate 0. In that case we
		* need to calibrate the rate instead.
		*/
		if (!IS_ERR_OR_NULL(twd_clk))
		twd_timer_rate = clk_get_rate(twd_clk);
		else
		twd_calibrate_rate();

		common_setup_called = true;
		}

		/*
		* The following is done once per CPU the first time .setup() is
		* called.
		*/
		__raw_writel(0, twd_base + TWD_TIMER_CONTROL);

		clk->name = "local_timer";

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