Commit ed26aacf authored by Serge Semin's avatar Serge Semin Committed by Thomas Bogendoerfer
Browse files

mips: Add udelay lpj numbers adjustment 



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: default avatarAlexey Malahov <Alexey.Malahov@baikalelectronics.ru>
Signed-off-by: default avatarAlexey Malahov <Alexey.Malahov@baikalelectronics.ru>
Signed-off-by: default avatarSerge Semin <Sergey.Semin@baikalelectronics.ru>
Reviewed-by: default avatarJiaxun 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: default avatarThomas Bogendoerfer <tsbogend@alpha.franken.de>
parent ad42e0a8

arch/mips/kernel/time.c

+70 −0
Original line number Diff line number Diff line
@@ -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

 */

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