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Subject[PATCH v4 11/13] mips: Add udelay lpj numbers adjustment
Date
Loops-per-jiffies is a special number which represents a number of
noop-loop cycles per CPU-scheduler quantum - jiffies. As you
understand aside from CPU-specific implementation it depends on
the CPU frequency. So when a platform has the CPU frequency fixed,
we have no problem and the current udelay interface will work
just fine. But as soon as CPU-freq driver is enabled and the cores
frequency changes, we'll end up with distorted udelay's. In order
to fix this we have to accordinly adjust the per-CPU udelay_val
(the same as the global loops_per_jiffy) number. This can be done
in the CPU-freq transition event handler. We subscribe to that event
in the MIPS arch time-inititalization method.

Co-developed-by: Alexey Malahov <Alexey.Malahov@baikalelectronics.ru>
Signed-off-by: Alexey Malahov <Alexey.Malahov@baikalelectronics.ru>
Signed-off-by: Serge Semin <Sergey.Semin@baikalelectronics.ru>
Reviewed-by: Jiaxun Yang <jiaxun.yang@flygoat.com>
Cc: Thomas Bogendoerfer <tsbogend@alpha.franken.de>
Cc: Paul Burton <paulburton@kernel.org>
Cc: Ralf Baechle <ralf@linux-mips.org>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Rob Herring <robh+dt@kernel.org>
Cc: devicetree@vger.kernel.org
---
arch/mips/kernel/time.c | 70 +++++++++++++++++++++++++++++++++++++++++
1 file changed, 70 insertions(+)

diff --git a/arch/mips/kernel/time.c b/arch/mips/kernel/time.c
index 37e9413a393d..caa01457dce6 100644
--- a/arch/mips/kernel/time.c
+++ b/arch/mips/kernel/time.c
@@ -18,12 +18,82 @@
#include <linux/smp.h>
#include <linux/spinlock.h>
#include <linux/export.h>
+#include <linux/cpufreq.h>
+#include <linux/delay.h>

#include <asm/cpu-features.h>
#include <asm/cpu-type.h>
#include <asm/div64.h>
#include <asm/time.h>

+#ifdef CONFIG_CPU_FREQ
+
+static DEFINE_PER_CPU(unsigned long, pcp_lpj_ref);
+static DEFINE_PER_CPU(unsigned long, pcp_lpj_ref_freq);
+static unsigned long glb_lpj_ref;
+static unsigned long glb_lpj_ref_freq;
+
+static int cpufreq_callback(struct notifier_block *nb,
+ unsigned long val, void *data)
+{
+ struct cpufreq_freqs *freq = data;
+ struct cpumask *cpus = freq->policy->cpus;
+ unsigned long lpj;
+ int cpu;
+
+ /*
+ * Skip lpj numbers adjustment if the CPU-freq transition is safe for
+ * the loops delay. (Is this possible?)
+ */
+ if (freq->flags & CPUFREQ_CONST_LOOPS)
+ return NOTIFY_OK;
+
+ /* Save the initial values of the lpjes for future scaling. */
+ if (!glb_lpj_ref) {
+ glb_lpj_ref = boot_cpu_data.udelay_val;
+ glb_lpj_ref_freq = freq->old;
+
+ for_each_online_cpu(cpu) {
+ per_cpu(pcp_lpj_ref, cpu) =
+ cpu_data[cpu].udelay_val;
+ per_cpu(pcp_lpj_ref_freq, cpu) = freq->old;
+ }
+ }
+
+ /*
+ * Adjust global lpj variable and per-CPU udelay_val number in
+ * accordance with the new CPU frequency.
+ */
+ if ((val == CPUFREQ_PRECHANGE && freq->old < freq->new) ||
+ (val == CPUFREQ_POSTCHANGE && freq->old > freq->new)) {
+ loops_per_jiffy = cpufreq_scale(glb_lpj_ref,
+ glb_lpj_ref_freq,
+ freq->new);
+
+ for_each_cpu(cpu, cpus) {
+ lpj = cpufreq_scale(per_cpu(pcp_lpj_ref, cpu),
+ per_cpu(pcp_lpj_ref_freq, cpu),
+ freq->new);
+ cpu_data[cpu].udelay_val = (unsigned int)lpj;
+ }
+ }
+
+ return NOTIFY_OK;
+}
+
+static struct notifier_block cpufreq_notifier = {
+ .notifier_call = cpufreq_callback,
+};
+
+static int __init register_cpufreq_notifier(void)
+{
+ return cpufreq_register_notifier(&cpufreq_notifier,
+ CPUFREQ_TRANSITION_NOTIFIER);
+}
+core_initcall(register_cpufreq_notifier);
+
+#endif /* CONFIG_CPU_FREQ */
+
/*
* forward reference
*/
--
2.25.1
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