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

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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: Colin Cross <ccross@android.com>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
This commit is contained in:
Colin Cross
2012-08-07 19:05:10 +01:00
committed by Russell King
parent f1898f6be9
commit 237ec6f2e5
2 changed files with 26 additions and 0 deletions
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2
arch/arm/include/asm/sched_clock.h
View File

@@ -10,5 +10,7 @@
extern void sched_clock_postinit(void); extern void sched_clock_postinit(void);
extern void setup_sched_clock(u32 (*read)(void), int bits, unsigned long rate); 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 #endif

24
arch/arm/kernel/sched_clock.c
View File

@@ -21,6 +21,8 @@ struct clock_data {
u32 epoch_cyc_copy; u32 epoch_cyc_copy;
u32 mult; u32 mult;
u32 shift; u32 shift;
bool suspended;
bool needs_suspend;
}; };
static void sched_clock_poll(unsigned long wrap_ticks); 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; u64 epoch_ns;
u32 epoch_cyc; u32 epoch_cyc;
if (cd.suspended)
return cd.epoch_ns;
/* /*
* Load the epoch_cyc and epoch_ns atomically. We do this by * Load the epoch_cyc and epoch_ns atomically. We do this by
* ensuring that we always write epoch_cyc, epoch_ns and * 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(); 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) void __init setup_sched_clock(u32 (*read)(void), int bits, unsigned long rate)
{ {
unsigned long r, w; unsigned long r, w;
@@ -169,11 +181,23 @@ void __init sched_clock_postinit(void)
static int sched_clock_suspend(void) static int sched_clock_suspend(void)
{ {
sched_clock_poll(sched_clock_timer.data); sched_clock_poll(sched_clock_timer.data);
if (cd.needs_suspend)
cd.suspended = true;
return 0; 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 = { static struct syscore_ops sched_clock_ops = {
.suspend = sched_clock_suspend, .suspend = sched_clock_suspend,
.resume = sched_clock_resume,
}; };
static int __init sched_clock_syscore_init(void) static int __init sched_clock_syscore_init(void)