src/arch/arm64/arch_timer.c

   1 /* SPDX-License-Identifier: GPL-2.0-only */
   2
   3 #include <arch/lib_helpers.h>
   4 #include <commonlib/bsd/gcd.h>
   5 #include <timer.h>
   6
   7 void timer_monotonic_get(struct mono_time *mt)
   8 {
   9         uint64_t tvalue = raw_read_cntpct_el0();
  10         static uint32_t tfreq, mult;
  11         uint32_t div;
  12
  13         /*
  14          * The value from raw_read_cntfrq_el0() could be large enough to
  15          * cause overflow when multiplied by USECS_PER_SEC. To prevent this,
  16          * both USECS_PER_SEC. and tfreq can be reduced by dividing them by
  17          * their GCD.
  18          */
  19         if (tfreq == 0) {
  20                 tfreq = raw_read_cntfrq_el0();
  21                 mult = USECS_PER_SEC;
  22                 div = gcd(tfreq, mult);
  23                 tfreq /= div;
  24                 mult /= div;
  25         }
  26
  27         long usecs = (tvalue * mult) / tfreq;
  28         mono_time_set_usecs(mt, usecs);
  29 }