ARM: tegra: cpuidle: Handle case where secondary CPU hangs on entering LP2

It is possible that something may go wrong with the secondary CPU, in
that case it is much nicer to get a dump of the flow-controller state
before hanging machine.
Acked-by: Peter De Schrijver <pdeschrijver@nvidia.com>
Tested-by: Peter Geis <pgwipeout@gmail.com>
Tested-by: Jasper Korten <jja2000@gmail.com>
Tested-by: David Heidelberg <david@ixit.cz>
Tested-by: Nicolas Chauvet <kwizart@gmail.com>
Acked-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Signed-off-by: Dmitry Osipenko <digetx@gmail.com>
Signed-off-by: Thierry Reding <treding@nvidia.com>

arch/arm/mach-tegra/cpuidle-tegra20.c

@@ -14,6 +14,7 @@
 #include <linux/tick.h>
 #include <linux/cpuidle.h>
 #include <linux/cpu_pm.h>
+#include <linux/delay.h>
 #include <linux/kernel.h>
 #include <linux/module.h>
 
@@ -82,14 +83,60 @@ static inline void tegra20_wake_cpu1_from_reset(void)
 }
 #endif
 
+static void tegra20_report_cpus_state(void)
+{
+	unsigned long cpu, lcpu, csr;
+
+	for_each_cpu(lcpu, cpu_possible_mask) {
+		cpu = cpu_logical_map(lcpu);
+		csr = flowctrl_read_cpu_csr(cpu);
+
+		pr_err("cpu%lu: online=%d flowctrl_csr=0x%08lx\n",
+		       cpu, cpu_online(lcpu), csr);
+	}
+}
+
+static int tegra20_wait_for_secondary_cpu_parking(void)
+{
+	unsigned int retries = 3;
+
+	while (retries--) {
+		unsigned int delay_us = 10;
+		unsigned int timeout_us = 500 * 1000 / delay_us;
+
+		/*
+		 * The primary CPU0 core shall wait for the secondaries
+		 * shutdown in order to power-off CPU's cluster safely.
+		 * The timeout value depends on the current CPU frequency,
+		 * it takes about 40-150us  in average and over 1000us in
+		 * a worst case scenario.
+		 */
+		do {
+			if (tegra_cpu_rail_off_ready())
+				return 0;
+
+			udelay(delay_us);
+
+		} while (timeout_us--);
+
+		pr_err("secondary CPU taking too long to park\n");
+
+		tegra20_report_cpus_state();
+	}
+
+	pr_err("timed out waiting secondaries to park\n");
+
+	return -ETIMEDOUT;
+}
+
 static bool tegra20_cpu_cluster_power_down(struct cpuidle_device *dev,
 					   struct cpuidle_driver *drv,
 					   int index)
 {
 	bool ret;
 
-	while (!tegra_cpu_rail_off_ready())
-		cpu_relax();
+	if (tegra20_wait_for_secondary_cpu_parking())
+		return false;
 
 	ret = !tegra_pm_enter_lp2();