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       1                 :            : /* SPDX-License-Identifier: GPL-2.0-or-later */
       2                 :            : /*
       3                 :            :  * linux/include/linux/timecounter.h
       4                 :            :  *
       5                 :            :  * based on code that migrated away from
       6                 :            :  * linux/include/linux/clocksource.h
       7                 :            :  */
       8                 :            : #ifndef _LINUX_TIMECOUNTER_H
       9                 :            : #define _LINUX_TIMECOUNTER_H
      10                 :            : 
      11                 :            : #include <linux/types.h>
      12                 :            : 
      13                 :            : /* simplify initialization of mask field */
      14                 :            : #define CYCLECOUNTER_MASK(bits) (u64)((bits) < 64 ? ((1ULL<<(bits))-1) : -1)
      15                 :            : 
      16                 :            : /**
      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.
      22                 :            :  *
      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)
      29                 :            :  */
      30                 :            : struct cyclecounter {
      31                 :            :         u64 (*read)(const struct cyclecounter *cc);
      32                 :            :         u64 mask;
      33                 :            :         u32 mult;
      34                 :            :         u32 shift;
      35                 :            : };
      36                 :            : 
      37                 :            : /**
      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.
      47                 :            :  *
      48                 :            :  * @cc:                 the cycle counter used by this instance
      49                 :            :  * @cycle_last:         most recent cycle counter value seen by
      50                 :            :  *                      timecounter_read()
      51                 :            :  * @nsec:               continuously increasing count
      52                 :            :  * @mask:               bit mask for maintaining the 'frac' field
      53                 :            :  * @frac:               accumulated fractional nanoseconds
      54                 :            :  */
      55                 :            : struct timecounter {
      56                 :            :         const struct cyclecounter *cc;
      57                 :            :         u64 cycle_last;
      58                 :            :         u64 nsec;
      59                 :            :         u64 mask;
      60                 :            :         u64 frac;
      61                 :            : };
      62                 :            : 
      63                 :            : /**
      64                 :            :  * cyclecounter_cyc2ns - converts cycle counter cycles to nanoseconds
      65                 :            :  * @cc:         Pointer to cycle counter.
      66                 :            :  * @cycles:     Cycles
      67                 :            :  * @mask:       bit mask for maintaining the 'frac' field
      68                 :            :  * @frac:       pointer to storage for the fractional nanoseconds.
      69                 :            :  */
      70                 :            : static inline u64 cyclecounter_cyc2ns(const struct cyclecounter *cc,
      71                 :            :                                       u64 cycles, u64 mask, u64 *frac)
      72                 :            : {
      73                 :            :         u64 ns = (u64) cycles;
      74                 :            : 
      75                 :          0 :         ns = (ns * cc->mult) + *frac;
      76                 :          0 :         *frac = ns & mask;
      77                 :          0 :         return ns >> cc->shift;
      78                 :            : }
      79                 :            : 
      80                 :            : /**
      81                 :            :  * timecounter_adjtime - Shifts the time of the clock.
      82                 :            :  * @delta:      Desired change in nanoseconds.
      83                 :            :  */
      84                 :            : static inline void timecounter_adjtime(struct timecounter *tc, s64 delta)
      85                 :            : {
      86                 :            :         tc->nsec += delta;
      87                 :            : }
      88                 :            : 
      89                 :            : /**
      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.
      94                 :            :  *
      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.
      98                 :            :  */
      99                 :            : extern void timecounter_init(struct timecounter *tc,
     100                 :            :                              const struct cyclecounter *cc,
     101                 :            :                              u64 start_tstamp);
     102                 :            : 
     103                 :            : /**
     104                 :            :  * timecounter_read - return nanoseconds elapsed since timecounter_init()
     105                 :            :  *                    plus the initial time stamp
     106                 :            :  * @tc:          Pointer to time counter.
     107                 :            :  *
     108                 :            :  * In other words, keeps track of time since the same epoch as
     109                 :            :  * the function which generated the initial time stamp.
     110                 :            :  */
     111                 :            : extern u64 timecounter_read(struct timecounter *tc);
     112                 :            : 
     113                 :            : /**
     114                 :            :  * timecounter_cyc2time - convert a cycle counter to same
     115                 :            :  *                        time base as values returned by
     116                 :            :  *                        timecounter_read()
     117                 :            :  * @tc:         Pointer to time counter.
     118                 :            :  * @cycle_tstamp:       a value returned by tc->cc->read()
     119                 :            :  *
     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.
     123                 :            :  *
     124                 :            :  * This allows conversion of cycle counter values which were generated
     125                 :            :  * in the past.
     126                 :            :  */
     127                 :            : extern u64 timecounter_cyc2time(struct timecounter *tc,
     128                 :            :                                 u64 cycle_tstamp);
     129                 :            : 
     130                 :            : #endif