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mips: Add udelay lpj numbers adjustment

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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
Signed-off-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>
This commit is contained in:
Serge Semin 2020-05-21 17:07:22 +03:00 committed by Thomas Bogendoerfer
parent ad42e0a8d4
commit ed26aacfb5
1 changed files with 70 additions and 0 deletions
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70
arch/mips/kernel/time.c
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@ -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
*/