From mboxrd@z Thu Jan 1 00:00:00 1970 From: ccross@android.com (Colin Cross) Date: Tue, 17 Jul 2012 16:27:51 -0700 Subject: [RFC] ARM: sched_clock: update epoch_cyc on resume Message-ID: <1342567672-29071-1-git-send-email-ccross@android.com> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org 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. This will have a side effect of causing SoCs that have clocks that continue to count in suspend to appear to stop counting, reporting the same sched_clock() value before and after suspend. Signed-off-by: Colin Cross --- arch/arm/kernel/sched_clock.c | 13 +++++++++++++ 1 files changed, 13 insertions(+), 0 deletions(-) diff --git a/arch/arm/kernel/sched_clock.c b/arch/arm/kernel/sched_clock.c index 27d186a..46c7d32 100644 --- a/arch/arm/kernel/sched_clock.c +++ b/arch/arm/kernel/sched_clock.c @@ -21,6 +21,7 @@ struct clock_data { u32 epoch_cyc_copy; u32 mult; u32 shift; + bool suspended; }; static void sched_clock_poll(unsigned long wrap_ticks); @@ -49,6 +50,9 @@ 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 @@ -169,11 +173,20 @@ void __init sched_clock_postinit(void) static int sched_clock_suspend(void) { sched_clock_poll(sched_clock_timer.data); + cd.suspended = true; return 0; } +static void sched_clock_resume(void) +{ + 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) -- 1.7.7.3