]>
git.proxmox.com Git - mirror_ubuntu-jammy-kernel.git/blob - include/linux/timecounter.h
1 /* SPDX-License-Identifier: GPL-2.0-or-later */
3 * linux/include/linux/timecounter.h
5 * based on code that migrated away from
6 * linux/include/linux/clocksource.h
8 #ifndef _LINUX_TIMECOUNTER_H
9 #define _LINUX_TIMECOUNTER_H
11 #include <linux/types.h>
13 /* simplify initialization of mask field */
14 #define CYCLECOUNTER_MASK(bits) (u64)((bits) < 64 ? ((1ULL<<(bits))-1) : -1)
17 * struct cyclecounter - hardware abstraction for a free running counter
18 * Provides completely state-free accessors to the underlying hardware.
19 * Depending on which hardware it reads, the cycle counter may wrap
20 * around quickly. Locking rules (if necessary) have to be defined
21 * by the implementor and user of specific instances of this API.
23 * @read: returns the current cycle value
24 * @mask: bitmask for two's complement
25 * subtraction of non 64 bit counters,
26 * see CYCLECOUNTER_MASK() helper macro
27 * @mult: cycle to nanosecond multiplier
28 * @shift: cycle to nanosecond divisor (power of two)
31 u64 (*read
)(const struct cyclecounter
*cc
);
38 * struct timecounter - layer above a %struct cyclecounter which counts nanoseconds
39 * Contains the state needed by timecounter_read() to detect
40 * cycle counter wrap around. Initialize with
41 * timecounter_init(). Also used to convert cycle counts into the
42 * corresponding nanosecond counts with timecounter_cyc2time(). Users
43 * of this code are responsible for initializing the underlying
44 * cycle counter hardware, locking issues and reading the time
45 * more often than the cycle counter wraps around. The nanosecond
46 * counter will only wrap around after ~585 years.
48 * @cc: the cycle counter used by this instance
49 * @cycle_last: most recent cycle counter value seen by
51 * @nsec: continuously increasing count
52 * @mask: bit mask for maintaining the 'frac' field
53 * @frac: accumulated fractional nanoseconds
56 const struct cyclecounter
*cc
;
64 * cyclecounter_cyc2ns - converts cycle counter cycles to nanoseconds
65 * @cc: Pointer to cycle counter.
67 * @mask: bit mask for maintaining the 'frac' field
68 * @frac: pointer to storage for the fractional nanoseconds.
70 static inline u64
cyclecounter_cyc2ns(const struct cyclecounter
*cc
,
71 u64 cycles
, u64 mask
, u64
*frac
)
73 u64 ns
= (u64
) cycles
;
75 ns
= (ns
* cc
->mult
) + *frac
;
77 return ns
>> cc
->shift
;
81 * timecounter_adjtime - Shifts the time of the clock.
82 * @delta: Desired change in nanoseconds.
84 static inline void timecounter_adjtime(struct timecounter
*tc
, s64 delta
)
90 * timecounter_init - initialize a time counter
91 * @tc: Pointer to time counter which is to be initialized/reset
92 * @cc: A cycle counter, ready to be used.
93 * @start_tstamp: Arbitrary initial time stamp.
95 * After this call the current cycle register (roughly) corresponds to
96 * the initial time stamp. Every call to timecounter_read() increments
97 * the time stamp counter by the number of elapsed nanoseconds.
99 extern void timecounter_init(struct timecounter
*tc
,
100 const struct cyclecounter
*cc
,
104 * timecounter_read - return nanoseconds elapsed since timecounter_init()
105 * plus the initial time stamp
106 * @tc: Pointer to time counter.
108 * In other words, keeps track of time since the same epoch as
109 * the function which generated the initial time stamp.
111 extern u64
timecounter_read(struct timecounter
*tc
);
114 * timecounter_cyc2time - convert a cycle counter to same
115 * time base as values returned by
117 * @tc: Pointer to time counter.
118 * @cycle_tstamp: a value returned by tc->cc->read()
120 * Cycle counts that are converted correctly as long as they
121 * fall into the interval [-1/2 max cycle count, +1/2 max cycle count],
122 * with "max cycle count" == cs->mask+1.
124 * This allows conversion of cycle counter values which were generated
127 extern u64
timecounter_cyc2time(const struct timecounter
*tc
,