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    Subject[PATCH AUTOSEL 5.4 134/175] mips: Add udelay lpj numbers adjustment
    Date
    From: Serge Semin <Sergey.Semin@baikalelectronics.ru>

    [ Upstream commit ed26aacfb5f71eecb20a51c4467da440cb719d66 ]

    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>
    Signed-off-by: Sasha Levin <sashal@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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