cachepc-linux

Fork of AMDESE/linux with modifications for CachePC side-channel attack
git clone https://git.sinitax.com/sinitax/cachepc-linux
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timecounter.c (2568B)

      1// SPDX-License-Identifier: GPL-2.0+
      2/*
      3 * Based on clocksource code. See commit 74d23cc704d1
      4 */
      5#include <linux/export.h>
      6#include <linux/timecounter.h>
      7
      8void timecounter_init(struct timecounter *tc,
      9		      const struct cyclecounter *cc,
     10		      u64 start_tstamp)
     11{
     12	tc->cc = cc;
     13	tc->cycle_last = cc->read(cc);
     14	tc->nsec = start_tstamp;
     15	tc->mask = (1ULL << cc->shift) - 1;
     16	tc->frac = 0;
     17}
     18EXPORT_SYMBOL_GPL(timecounter_init);
     19
     20/**
     21 * timecounter_read_delta - get nanoseconds since last call of this function
     22 * @tc:         Pointer to time counter
     23 *
     24 * When the underlying cycle counter runs over, this will be handled
     25 * correctly as long as it does not run over more than once between
     26 * calls.
     27 *
     28 * The first call to this function for a new time counter initializes
     29 * the time tracking and returns an undefined result.
     30 */
     31static u64 timecounter_read_delta(struct timecounter *tc)
     32{
     33	u64 cycle_now, cycle_delta;
     34	u64 ns_offset;
     35
     36	/* read cycle counter: */
     37	cycle_now = tc->cc->read(tc->cc);
     38
     39	/* calculate the delta since the last timecounter_read_delta(): */
     40	cycle_delta = (cycle_now - tc->cycle_last) & tc->cc->mask;
     41
     42	/* convert to nanoseconds: */
     43	ns_offset = cyclecounter_cyc2ns(tc->cc, cycle_delta,
     44					tc->mask, &tc->frac);
     45
     46	/* update time stamp of timecounter_read_delta() call: */
     47	tc->cycle_last = cycle_now;
     48
     49	return ns_offset;
     50}
     51
     52u64 timecounter_read(struct timecounter *tc)
     53{
     54	u64 nsec;
     55
     56	/* increment time by nanoseconds since last call */
     57	nsec = timecounter_read_delta(tc);
     58	nsec += tc->nsec;
     59	tc->nsec = nsec;
     60
     61	return nsec;
     62}
     63EXPORT_SYMBOL_GPL(timecounter_read);
     64
     65/*
     66 * This is like cyclecounter_cyc2ns(), but it is used for computing a
     67 * time previous to the time stored in the cycle counter.
     68 */
     69static u64 cc_cyc2ns_backwards(const struct cyclecounter *cc,
     70			       u64 cycles, u64 mask, u64 frac)
     71{
     72	u64 ns = (u64) cycles;
     73
     74	ns = ((ns * cc->mult) - frac) >> cc->shift;
     75
     76	return ns;
     77}
     78
     79u64 timecounter_cyc2time(const struct timecounter *tc,
     80			 u64 cycle_tstamp)
     81{
     82	u64 delta = (cycle_tstamp - tc->cycle_last) & tc->cc->mask;
     83	u64 nsec = tc->nsec, frac = tc->frac;
     84
     85	/*
     86	 * Instead of always treating cycle_tstamp as more recent
     87	 * than tc->cycle_last, detect when it is too far in the
     88	 * future and treat it as old time stamp instead.
     89	 */
     90	if (delta > tc->cc->mask / 2) {
     91		delta = (tc->cycle_last - cycle_tstamp) & tc->cc->mask;
     92		nsec -= cc_cyc2ns_backwards(tc->cc, delta, tc->mask, frac);
     93	} else {
     94		nsec += cyclecounter_cyc2ns(tc->cc, delta, tc->mask, &frac);
     95	}
     96
     97	return nsec;
     98}
     99EXPORT_SYMBOL_GPL(timecounter_cyc2time);