Line data    Source code

       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           0 : static inline u64 cyclecounter_cyc2ns(const struct cyclecounter *cc,
      71             :                                       u64 cycles, u64 mask, u64 *frac)
      72             : {
      73           0 :         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