mips: cevt-r4k: Update the r4k-clockevent frequency in sync with CPU

Due to being embedded into the CPU cores MIPS count/compare timer
frequency is changed together with the CPU clocks alteration.
In case if frequency really changes the kernel clockevent framework
must be notified, otherwise the kernel timers won't work correctly.
Fix this by calling clockevents_update_freq() for each r4k clockevent
handlers registered per available CPUs.

Traditionally MIPS r4k-clock are clocked with CPU frequency divided by 2.
But this isn't true for some of the platforms. Due to this we have to save
the basic CPU frequency, so then use it to scale the initial timer
frequency (mips_hpt_frequency) and pass the updated value further to the
clockevent framework.
Signed-off-by: Serge Semin <Sergey.Semin@baikalelectronics.ru>
Cc: Alexey Malahov <Alexey.Malahov@baikalelectronics.ru>
Cc: Thomas Bogendoerfer <tsbogend@alpha.franken.de>
Cc: Paul Burton <paulburton@kernel.org>
Cc: Ralf Baechle <ralf@linux-mips.org>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Rob Herring <robh+dt@kernel.org>
Cc: devicetree@vger.kernel.org
Signed-off-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>

arch/mips/kernel/cevt-r4k.c

@@ -8,6 +8,7 @@
  */
 #include <linux/clockchips.h>
 #include <linux/interrupt.h>
+#include <linux/cpufreq.h>
 #include <linux/percpu.h>
 #include <linux/smp.h>
 #include <linux/irq.h>
@@ -250,6 +251,49 @@ unsigned int __weak get_c0_compare_int(void)
 	return MIPS_CPU_IRQ_BASE + cp0_compare_irq;
 }
 
+#ifdef CONFIG_CPU_FREQ
+
+static unsigned long mips_ref_freq;
+
+static int r4k_cpufreq_callback(struct notifier_block *nb,
+				unsigned long val, void *data)
+{
+	struct cpufreq_freqs *freq = data;
+	struct clock_event_device *cd;
+	unsigned long rate;
+	int cpu;
+
+	if (!mips_ref_freq)
+		mips_ref_freq = freq->old;
+
+	if (val == CPUFREQ_POSTCHANGE) {
+		rate = cpufreq_scale(mips_hpt_frequency, mips_ref_freq,
+				     freq->new);
+
+		for_each_cpu(cpu, freq->policy->cpus) {
+			cd = &per_cpu(mips_clockevent_device, cpu);
+
+			clockevents_update_freq(cd, rate);
+		}
+	}
+
+	return 0;
+}
+
+static struct notifier_block r4k_cpufreq_notifier = {
+	.notifier_call  = r4k_cpufreq_callback,
+};
+
+static int __init r4k_register_cpufreq_notifier(void)
+{
+	return cpufreq_register_notifier(&r4k_cpufreq_notifier,
+					 CPUFREQ_TRANSITION_NOTIFIER);
+
+}
+core_initcall(r4k_register_cpufreq_notifier);
+
+#endif /* !CONFIG_CPU_FREQ */
+
 int r4k_clockevent_init(void)
 {
 	unsigned long flags = IRQF_PERCPU | IRQF_TIMER | IRQF_SHARED;