On some hardware with multiple clocksources, we have course grained
clocksources that support the CLOCK_SOURCE_SUSPEND_NONSTOP flag, but
which are less ideal for timekeeping then other clocksources which
halt in suspend.
Currently, the timekeeping core only supports timing suspend using
CLOCK_SOURCE_SUSPEND_NONSTOP clocksources if that clocksource is the
current clocksource for timekeeping.
As a result, some architectures try to implement read_persisitent_clock64()
using those non-stop clocksources, but isn't really ideal. Thus this
patch provides logic to allow a registered SUSPEND_NONSTOP clocksource,
which isn't the current clocksource, to be used to calculate the suspend
time.
Suggested-by: Thomas Gleixner <t...@linutronix.de>
Signed-off-by: Baolin Wang <baolin.w...@linaro.org>
---
include/linux/clocksource.h | 3 +
kernel/time/clocksource.c | 152 +++++++++++++++++++++++++++++++++++++++++++
kernel/time/timekeeping.c | 22 ++++---
3 files changed, 169 insertions(+), 8 deletions(-)
diff --git a/include/linux/clocksource.h b/include/linux/clocksource.h
index 7dff196..3089189 100644
--- a/include/linux/clocksource.h
+++ b/include/linux/clocksource.h
@@ -194,6 +194,9 @@ static inline s64 clocksource_cyc2ns(u64 cycles, u32 mult,
u32 shift)
extern void clocksource_resume(void);
extern struct clocksource * __init clocksource_default_clock(void);
extern void clocksource_mark_unstable(struct clocksource *cs);
+extern void
+clocksource_start_suspend_timing(struct clocksource *cs, u64 start_cycles);
+extern u64 clocksource_stop_suspend_timing(struct clocksource *cs, u64 now);
extern u64
clocks_calc_max_nsecs(u32 mult, u32 shift, u32 maxadj, u64 mask, u64
*max_cycles);
diff --git a/kernel/time/clocksource.c b/kernel/time/clocksource.c
index f89a78e..7778eaa 100644
--- a/kernel/time/clocksource.c
+++ b/kernel/time/clocksource.c
@@ -94,6 +94,8 @@
/*[Clocksource internal variables]---------
* curr_clocksource:
* currently selected clocksource.
+ * suspend_clocksource:
+ * used to calculate the suspend time.
* clocksource_list:
* linked list with the registered clocksources
* clocksource_mutex:
@@ -102,10 +104,12 @@
* Name of the user-specified clocksource.
*/
static struct clocksource *curr_clocksource;
+static struct clocksource *suspend_clocksource;
static LIST_HEAD(clocksource_list);
static DEFINE_MUTEX(clocksource_mutex);
static char override_name[CS_NAME_LEN];
static int finished_booting;
+static u64 suspend_start;
#ifdef CONFIG_CLOCKSOURCE_WATCHDOG
static void clocksource_watchdog_work(struct work_struct *work);
@@ -447,6 +451,133 @@ static inline void clocksource_watchdog_unlock(unsigned
long *flags) { }
#endif /* CONFIG_CLOCKSOURCE_WATCHDOG */
+static bool clocksource_is_suspend(struct clocksource *cs)
+{
+ return cs == suspend_clocksource;
+}
+
+static void __clocksource_suspend_select(struct clocksource *cs)
+{
+ /*
+ * Skip the clocksource which will be stopped in suspend state.
+ */
+ if (!(cs->flags & CLOCK_SOURCE_SUSPEND_NONSTOP))
+ return;
+
+ /* Pick the best rating. */
+ if (!suspend_clocksource || cs->rating > suspend_clocksource->rating)
+ suspend_clocksource = cs;
+}
+
+/**
+ * clocksource_suspend_select - Select the best clocksource for suspend timing
+ * @fallback: if select a fallback clocksource
+ */
+static void clocksource_suspend_select(bool fallback)
+{
+ struct clocksource *cs, *old_suspend;
+
+ old_suspend = suspend_clocksource;
+ if (fallback)
+ suspend_clocksource = NULL;
+
+ list_for_each_entry(cs, &clocksource_list, list) {
+ /* Skip current if we were requested for a fallback. */
+ if (fallback && cs == old_suspend)
+ continue;
+
+ __clocksource_suspend_select(cs);
+ }
+
+ /* If we failed to find a fallback restore the old one. */
+ if (!suspend_clocksource)
+ suspend_clocksource = old_suspend;
+}
+
+/**
+ * clocksource_start_suspend_timing - Start measuring the suspend timing
+ * @cs: current clocksource from timekeeping
+ * @start_cycles: current cycles from timekeeping
+ *
+ * This function will save the start cycle values of suspend timer to calculate
+ * the suspend time when resuming system.
+ *
+ * This function is called late in the suspend process from
timekeeping_suspend(),
+ * that means processes are freezed, non-boot cpus and interrupts are disabled
+ * now. It is therefore possible to start the suspend timer without taking the
+ * clocksource mutex.
+ */
+void clocksource_start_suspend_timing(struct clocksource *cs, u64 start_cycles)
+{
+ if (!suspend_clocksource)
+ return;
+
+ /*
+ * If current clocksource is the suspend timer, we should use the
+ * tkr_mono.cycle_last value as suspend_start to avoid same reading
+ * from suspend timer.
+ */
+ if (clocksource_is_suspend(cs)) {
+ suspend_start = start_cycles;
+ return;
+ }
+
+ if (suspend_clocksource->enable &&
+ WARN_ON_ONCE(suspend_clocksource->enable(suspend_clocksource))) {
+ pr_warn_once("Failed to enable the non-suspend-able
clocksource.\n");
+ return;
+ }
+
+ suspend_start = suspend_clocksource->read(suspend_clocksource);
+}
+
+/**
+ * clocksource_stop_suspend_timing - Stop measuring the suspend timing
+ * @cs: current clocksource from timekeeping
+ * @cycle_now: current cycles from timekeeping
+ *
+ * This function will calculate the suspend time from suspend timer, and return
+ * nanoseconds since suspend started or 0 if no usable clocksource.
+ *
+ * This function is called early in the resume process from
timekeeping_resume(),
+ * that means there is only one cpu, no processes are running and the
interrupts
+ * are disabled. It is therefore possible to stop the suspend timer without
+ * taking the clocksource mutex.
+ */
+u64 clocksource_stop_suspend_timing(struct clocksource *cs, u64 cycle_now)
+{
+ u64 now, delta, nsec = 0;
+
+ if (!suspend_clocksource)
+ return 0;
+
+ /*
+ * If current clocksource is the suspend timer, we should use the
+ * tkr_mono.cycle_last value from timekeeping as current cycle to
+ * avoid same reading from suspend timer.
+ */
+ if (clocksource_is_suspend(cs))
+ now = cycle_now;
+ else
+ now = suspend_clocksource->read(suspend_clocksource);
+
+ if (now > suspend_start) {
+ delta = clocksource_delta(now, suspend_start,
+ suspend_clocksource->mask);
+ nsec = mul_u64_u32_shr(delta, suspend_clocksource->mult,
+ suspend_clocksource->shift);
+ }
+
+ /*
+ * Disable the suspend timer to save power if current clocksource is
+ * not the suspend timer.
+ */
+ if (!clocksource_is_suspend(cs) && suspend_clocksource->disable)
+ suspend_clocksource->disable(suspend_clocksource);
+
+ return nsec;
+}
+
/**
* clocksource_suspend - suspend the clocksource(s)
*/
@@ -779,6 +910,16 @@ int __clocksource_register_scale(struct clocksource *cs,
u32 scale, u32 freq)
{
unsigned long flags;
+ /*
+ * The nonstop clocksource can be selected as the suspend clocksource to
+ * calculate the suspend time, so it should not supply suspend/resume
+ * interfaces to suspend the nonstop clocksource when system suspends.
+ */
+ if ((cs->flags & CLOCK_SOURCE_SUSPEND_NONSTOP) &&
+ (cs->suspend || cs->resume))
+ pr_warn("Nonstop clocksource %s should not supply
suspend/resume interfaces\n",
+ cs->name);
+
/* Initialize mult/shift and max_idle_ns */
__clocksource_update_freq_scale(cs, scale, freq);
@@ -792,6 +933,7 @@ int __clocksource_register_scale(struct clocksource *cs,
u32 scale, u32 freq)
clocksource_select();
clocksource_select_watchdog(false);
+ __clocksource_suspend_select(cs);
mutex_unlock(&clocksource_mutex);
return 0;
}
@@ -820,6 +962,7 @@ void clocksource_change_rating(struct clocksource *cs, int
rating)
clocksource_select();
clocksource_select_watchdog(false);
+ clocksource_suspend_select(false);
mutex_unlock(&clocksource_mutex);
}
EXPORT_SYMBOL(clocksource_change_rating);
@@ -838,6 +981,15 @@ static int clocksource_unbind(struct clocksource *cs)
return -EBUSY;
}
+ if (clocksource_is_suspend(cs)) {
+ /*
+ * Select and try to install a replacement suspend clocksource.
+ */
+ clocksource_suspend_select(true);
+ if (clocksource_is_suspend(cs))
+ return -EBUSY;
+ }
+
if (cs == curr_clocksource) {
/* Select and try to install a replacement clock source */
clocksource_select_fallback();
diff --git a/kernel/time/timekeeping.c b/kernel/time/timekeeping.c
index 4786df9..d80dba3 100644
--- a/kernel/time/timekeeping.c
+++ b/kernel/time/timekeeping.c
@@ -1669,7 +1669,7 @@ void timekeeping_resume(void)
struct clocksource *clock = tk->tkr_mono.clock;
unsigned long flags;
struct timespec64 ts_new, ts_delta;
- u64 cycle_now;
+ u64 cycle_now, nsec;
sleeptime_injected = false;
read_persistent_clock64(&ts_new);
@@ -1693,13 +1693,8 @@ void timekeeping_resume(void)
* usable source. The rtc part is handled separately in rtc core code.
*/
cycle_now = tk_clock_read(&tk->tkr_mono);
- if ((clock->flags & CLOCK_SOURCE_SUSPEND_NONSTOP) &&
- cycle_now > tk->tkr_mono.cycle_last) {
- u64 nsec, cyc_delta;
-
- cyc_delta = clocksource_delta(cycle_now,
tk->tkr_mono.cycle_last,
- tk->tkr_mono.mask);
- nsec = mul_u64_u32_shr(cyc_delta, clock->mult, clock->shift);
+ nsec = clocksource_stop_suspend_timing(clock, cycle_now);
+ if (nsec > 0) {
ts_delta = ns_to_timespec64(nsec);
sleeptime_injected = true;
} else if (timespec64_compare(&ts_new, &timekeeping_suspend_time) > 0) {
@@ -1732,6 +1727,8 @@ int timekeeping_suspend(void)
unsigned long flags;
struct timespec64 delta, delta_delta;
static struct timespec64 old_delta;
+ struct clocksource *curr_clock;
+ u64 cycle_now;
read_persistent_clock64(&timekeeping_suspend_time);
@@ -1748,6 +1745,15 @@ int timekeeping_suspend(void)
timekeeping_forward_now(tk);
timekeeping_suspended = 1;
+ /*
+ * Since we've called forward_now, cycle_last stores the value
+ * just read from the current clocksource. Save this to potentially
+ * use in suspend timing.
+ */
+ curr_clock = tk->tkr_mono.clock;
+ cycle_now = tk->tkr_mono.cycle_last;
+ clocksource_start_suspend_timing(curr_clock, cycle_now);
+
if (persistent_clock_exists) {
/*
* To avoid drift caused by repeated suspend/resumes,
--
1.7.9.5
