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 a6ebc8135112..df18f386d457 100644 --- a/arch/mips/kernel/time.c +++ b/arch/mips/kernel/time.c @@ -22,12 +22,82 @@ #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 */