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linux-next/include/linux/clockchips.h
Viresh Kumar 8fff52fd50 clockevents: Introduce CLOCK_EVT_STATE_ONESHOT_STOPPED state 
When no timers/hrtimers are pending, the expiry time is set to a
special value: 'KTIME_MAX'. This normally happens with
NO_HZ_{IDLE|FULL} in both LOWRES/HIGHRES modes.

When 'expiry == KTIME_MAX', we either cancel the 'tick-sched' hrtimer
(NOHZ_MODE_HIGHRES) or skip reprogramming clockevent device
(NOHZ_MODE_LOWRES).  But, the clockevent device is already
reprogrammed from the tick-handler for next tick.

As the clock event device is programmed in ONESHOT mode it will at
least fire one more time (unnecessarily). Timers on few
implementations (like arm_arch_timer, etc.) only support PERIODIC mode
and their drivers emulate ONESHOT over that. Which means that on these
platforms we will get spurious interrupts periodically (at last
programmed interval rate, normally tick rate).

In order to avoid spurious interrupts, the clockevent device should be
stopped or its interrupts should be masked.

A simple (yet hacky) solution to get this fixed could be: update
hrtimer_force_reprogram() to always reprogram clockevent device and
update clockevent drivers to STOP generating events (or delay it to
max time) when 'expires' is set to KTIME_MAX. But the drawback here is
that every clockevent driver has to be hacked for this particular case
and its very easy for new ones to miss this.

However, Thomas suggested to add an optional state ONESHOT_STOPPED to
solve this problem: lkml.org/lkml/2014/5/9/508.

This patch adds support for ONESHOT_STOPPED state in clockevents
core. It will only be available to drivers that implement the
state-specific callbacks instead of the legacy ->set_mode() callback.

Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>
Reviewed-by: Preeti U. Murthy <preeti@linux.vnet.ibm.com>
Cc: linaro-kernel@lists.linaro.org
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Kevin Hilman <khilman@linaro.org>
Cc: Daniel Lezcano <daniel.lezcano@linaro.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/b8b383a03ac07b13312c16850b5106b82e4245b5.1428031396.git.viresh.kumar@linaro.org
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
2015-05-19 16:18:02 +02:00

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/* linux/include/linux/clockchips.h
*
* This file contains the structure definitions for clockchips.
*
* If you are not a clockchip, or the time of day code, you should
* not be including this file!
*/
#ifndef _LINUX_CLOCKCHIPS_H
#define _LINUX_CLOCKCHIPS_H
#ifdef CONFIG_GENERIC_CLOCKEVENTS
# include <linux/clocksource.h>
# include <linux/cpumask.h>
# include <linux/ktime.h>
# include <linux/notifier.h>
struct clock_event_device;
struct module;
/* Clock event mode commands for legacy ->set_mode(): OBSOLETE */
enum clock_event_mode {
CLOCK_EVT_MODE_UNUSED,
CLOCK_EVT_MODE_SHUTDOWN,
CLOCK_EVT_MODE_PERIODIC,
CLOCK_EVT_MODE_ONESHOT,
CLOCK_EVT_MODE_RESUME,
};
/*
* Possible states of a clock event device.
*
* DETACHED: Device is not used by clockevents core. Initial state or can be
* reached from SHUTDOWN.
* SHUTDOWN: Device is powered-off. Can be reached from PERIODIC or ONESHOT.
* PERIODIC: Device is programmed to generate events periodically. Can be
* reached from DETACHED or SHUTDOWN.
* ONESHOT: Device is programmed to generate event only once. Can be reached
* from DETACHED or SHUTDOWN.
* ONESHOT_STOPPED: Device was programmed in ONESHOT mode and is temporarily
* stopped.
*/
enum clock_event_state {
CLOCK_EVT_STATE_DETACHED,
CLOCK_EVT_STATE_SHUTDOWN,
CLOCK_EVT_STATE_PERIODIC,
CLOCK_EVT_STATE_ONESHOT,
CLOCK_EVT_STATE_ONESHOT_STOPPED,
};
/*
* Clock event features
*/
# define CLOCK_EVT_FEAT_PERIODIC 0x000001
# define CLOCK_EVT_FEAT_ONESHOT 0x000002
# define CLOCK_EVT_FEAT_KTIME 0x000004
/*
* x86(64) specific (mis)features:
*
* - Clockevent source stops in C3 State and needs broadcast support.
* - Local APIC timer is used as a dummy device.
*/
# define CLOCK_EVT_FEAT_C3STOP 0x000008
# define CLOCK_EVT_FEAT_DUMMY 0x000010
/*
* Core shall set the interrupt affinity dynamically in broadcast mode
*/
# define CLOCK_EVT_FEAT_DYNIRQ 0x000020
# define CLOCK_EVT_FEAT_PERCPU 0x000040
/*
* Clockevent device is based on a hrtimer for broadcast
*/
# define CLOCK_EVT_FEAT_HRTIMER 0x000080
/**
* struct clock_event_device - clock event device descriptor
* @event_handler: Assigned by the framework to be called by the low
* level handler of the event source
* @set_next_event: set next event function using a clocksource delta
* @set_next_ktime: set next event function using a direct ktime value
* @next_event: local storage for the next event in oneshot mode
* @max_delta_ns: maximum delta value in ns
* @min_delta_ns: minimum delta value in ns
* @mult: nanosecond to cycles multiplier
* @shift: nanoseconds to cycles divisor (power of two)
* @mode: operating mode, relevant only to ->set_mode(), OBSOLETE
* @state: current state of the device, assigned by the core code
* @features: features
* @retries: number of forced programming retries
* @set_mode: legacy set mode function, only for modes <= CLOCK_EVT_MODE_RESUME.
* @set_state_periodic: switch state to periodic, if !set_mode
* @set_state_oneshot: switch state to oneshot, if !set_mode
* @set_state_oneshot_stopped: switch state to oneshot_stopped, if !set_mode
* @set_state_shutdown: switch state to shutdown, if !set_mode
* @tick_resume: resume clkevt device, if !set_mode
* @broadcast: function to broadcast events
* @min_delta_ticks: minimum delta value in ticks stored for reconfiguration
* @max_delta_ticks: maximum delta value in ticks stored for reconfiguration
* @name: ptr to clock event name
* @rating: variable to rate clock event devices
* @irq: IRQ number (only for non CPU local devices)
* @bound_on: Bound on CPU
* @cpumask: cpumask to indicate for which CPUs this device works
* @list: list head for the management code
* @owner: module reference
*/
struct clock_event_device {
void (*event_handler)(struct clock_event_device *);
int (*set_next_event)(unsigned long evt, struct clock_event_device *);
int (*set_next_ktime)(ktime_t expires, struct clock_event_device *);
ktime_t next_event;
u64 max_delta_ns;
u64 min_delta_ns;
u32 mult;
u32 shift;
enum clock_event_mode mode;
enum clock_event_state state;
unsigned int features;
unsigned long retries;
/*
* State transition callback(s): Only one of the two groups should be
* defined:
* - set_mode(), only for modes <= CLOCK_EVT_MODE_RESUME.
* - set_state_{shutdown|periodic|oneshot|oneshot_stopped}(), tick_resume().
*/
void (*set_mode)(enum clock_event_mode mode, struct clock_event_device *);
int (*set_state_periodic)(struct clock_event_device *);
int (*set_state_oneshot)(struct clock_event_device *);
int (*set_state_oneshot_stopped)(struct clock_event_device *);
int (*set_state_shutdown)(struct clock_event_device *);
int (*tick_resume)(struct clock_event_device *);
void (*broadcast)(const struct cpumask *mask);
void (*suspend)(struct clock_event_device *);
void (*resume)(struct clock_event_device *);
unsigned long min_delta_ticks;
unsigned long max_delta_ticks;
const char *name;
int rating;
int irq;
int bound_on;
const struct cpumask *cpumask;
struct list_head list;
struct module *owner;
} ____cacheline_aligned;
/*
* Calculate a multiplication factor for scaled math, which is used to convert
* nanoseconds based values to clock ticks:
*
* clock_ticks = (nanoseconds * factor) >> shift.
*
* div_sc is the rearranged equation to calculate a factor from a given clock
* ticks / nanoseconds ratio:
*
* factor = (clock_ticks << shift) / nanoseconds
*/
static inline unsigned long
div_sc(unsigned long ticks, unsigned long nsec, int shift)
{
u64 tmp = ((u64)ticks) << shift;
do_div(tmp, nsec);
return (unsigned long) tmp;
}
/* Clock event layer functions */
extern u64 clockevent_delta2ns(unsigned long latch, struct clock_event_device *evt);
extern void clockevents_register_device(struct clock_event_device *dev);
extern int clockevents_unbind_device(struct clock_event_device *ced, int cpu);
extern void clockevents_config(struct clock_event_device *dev, u32 freq);
extern void clockevents_config_and_register(struct clock_event_device *dev,
u32 freq, unsigned long min_delta,
unsigned long max_delta);
extern int clockevents_update_freq(struct clock_event_device *ce, u32 freq);
static inline void
clockevents_calc_mult_shift(struct clock_event_device *ce, u32 freq, u32 minsec)
{
return clocks_calc_mult_shift(&ce->mult, &ce->shift, NSEC_PER_SEC, freq, minsec);
}
extern void clockevents_suspend(void);
extern void clockevents_resume(void);
# ifdef CONFIG_GENERIC_CLOCKEVENTS_BROADCAST
# ifdef CONFIG_ARCH_HAS_TICK_BROADCAST
extern void tick_broadcast(const struct cpumask *mask);
# else
# define tick_broadcast NULL
# endif
extern int tick_receive_broadcast(void);
# endif
# if defined(CONFIG_GENERIC_CLOCKEVENTS_BROADCAST) && defined(CONFIG_TICK_ONESHOT)
extern void tick_setup_hrtimer_broadcast(void);
extern int tick_check_broadcast_expired(void);
# else
static inline int tick_check_broadcast_expired(void) { return 0; }
static inline void tick_setup_hrtimer_broadcast(void) { }
# endif
extern int clockevents_notify(unsigned long reason, void *arg);
#else /* !CONFIG_GENERIC_CLOCKEVENTS: */
static inline void clockevents_suspend(void) { }
static inline void clockevents_resume(void) { }
static inline int clockevents_notify(unsigned long reason, void *arg) { return 0; }
static inline int tick_check_broadcast_expired(void) { return 0; }
static inline void tick_setup_hrtimer_broadcast(void) { }
#endif /* !CONFIG_GENERIC_CLOCKEVENTS */
#endif /* _LINUX_CLOCKCHIPS_H */
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