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Commit 237ec6f2 authored by Colin Cross's avatar Colin Cross Committed by Russell King
Browse files

ARM: 7486/1: sched_clock: update epoch_cyc on resume 



Many clocks that are used to provide sched_clock will reset during
suspend.  If read_sched_clock returns 0 after suspend, sched_clock will
appear to jump forward.  This patch resets cd.epoch_cyc to the current
value of read_sched_clock during resume, which causes sched_clock() just
after suspend to return the same value as sched_clock() just before
suspend.

In addition, during the window where epoch_ns has been updated before
suspend, but epoch_cyc has not been updated after suspend, it is unknown
whether the clock has reset or not, and sched_clock() could return a
bogus value.  Add a suspended flag, and return the pre-suspend epoch_ns
value during this period.

The new behavior is triggered by calling setup_sched_clock_needs_suspend
instead of setup_sched_clock.

Signed-off-by: default avatarColin Cross <ccross@android.com>
Reviewed-by: default avatarLinus Walleij <linus.walleij@linaro.org>
Signed-off-by: default avatarRussell King <rmk+kernel@arm.linux.org.uk>
parent f1898f6b

arch/arm/include/asm/sched_clock.h

+2 −0
Original line number Diff line number Diff line
@@ -10,5 +10,7 @@ 


extern void sched_clock_postinit(void);

extern void setup_sched_clock(u32 (*read)(void), int bits, unsigned long rate);

extern void setup_sched_clock_needs_suspend(u32 (*read)(void), int bits,

		unsigned long rate);



#endif

arch/arm/kernel/sched_clock.c

+24 −0
Original line number Diff line number Diff line
@@ -21,6 +21,8 @@ struct clock_data { 
	u32 epoch_cyc_copy;

	u32 mult;

	u32 shift;

	bool suspended;

	bool needs_suspend;

};



static void sched_clock_poll(unsigned long wrap_ticks);
@@ -49,6 +51,9 @@ static unsigned long long cyc_to_sched_clock(u32 cyc, u32 mask) 
	u64 epoch_ns;

	u32 epoch_cyc;



	if (cd.suspended)

		return cd.epoch_ns;



	/*

	 * Load the epoch_cyc and epoch_ns atomically.  We do this by

	 * ensuring that we always write epoch_cyc, epoch_ns and
@@ -98,6 +103,13 @@ static void sched_clock_poll(unsigned long wrap_ticks) 
	update_sched_clock();

}



void __init setup_sched_clock_needs_suspend(u32 (*read)(void), int bits,

		unsigned long rate)

{

	setup_sched_clock(read, bits, rate);

	cd.needs_suspend = true;

}



void __init setup_sched_clock(u32 (*read)(void), int bits, unsigned long rate)

{

	unsigned long r, w;
@@ -169,11 +181,23 @@ void __init sched_clock_postinit(void) 
static int sched_clock_suspend(void)

{

	sched_clock_poll(sched_clock_timer.data);

	if (cd.needs_suspend)

		cd.suspended = true;

	return 0;

}



static void sched_clock_resume(void)

{

	if (cd.needs_suspend) {

		cd.epoch_cyc = read_sched_clock();

		cd.epoch_cyc_copy = cd.epoch_cyc;

		cd.suspended = false;

	}

}



static struct syscore_ops sched_clock_ops = {

	.suspend = sched_clock_suspend,

	.resume = sched_clock_resume,

};



static int __init sched_clock_syscore_init(void)