From a68becd1dcda55b467dcabaff136cadc10abb761 Mon Sep 17 00:00:00 2001 From: Linus Walleij Date: Tue, 23 Oct 2012 08:29:48 +0100 Subject: [PATCH] ARM: 7563/1: SMP_TWD: make setup()/stop() reentrant 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 Reported-by: Peter Chen Reviewed-by: Santosh Shilimkar Tested-by: Shawn Guo Signed-off-by: Linus Walleij Signed-off-by: Russell King --- arch/arm/kernel/smp_twd.c | 42 ++++++++++++++++++++++++++++++++++----- 1 file changed, 37 insertions(+), 5 deletions(-) diff --git a/arch/arm/kernel/smp_twd.c b/arch/arm/kernel/smp_twd.c index 780b0570636..a2e74375945 100644 --- a/arch/arm/kernel/smp_twd.c +++ b/arch/arm/kernel/smp_twd.c @@ -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(); - if (!IS_ERR_OR_NULL(twd_clk)) - twd_timer_rate = clk_get_rate(twd_clk); - else - twd_calibrate_rate(); + /* + * 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";