ALSA: es1968: Use monotonic clock

Commit Message

Abhilash Jindal Aug. 9, 2015, 1:48 a.m. UTC

Wall time obtained from do_gettimeofday is susceptible to sudden jumps due
to
user setting the time or due to NTP.

Monotonic time is constantly increasing time better suited
for comparing two timestamps.
---
 sound/pci/es1968.c |   14 +++++++-------
 1 file changed, 7 insertions(+), 7 deletions(-)

  chip->in_measurement = 0;
@@ -1776,11 +1776,11 @@ static void es1968_measure_clock(struct es1968
*chip)
  offset += chip->measure_count * (CLOCK_MEASURE_BUFSIZE/2);

  t = stop_time.tv_sec - start_time.tv_sec;
- t *= 1000000;
- if (stop_time.tv_usec < start_time.tv_usec)
- t -= start_time.tv_usec - stop_time.tv_usec;
+ t *= USEC_PER_SEC;
+ if (stop_time.tv_nsec < start_time.tv_nsec)
+ t -= (start_time.tv_nsec - stop_time.tv_nsec)/NSEC_PER_USEC;
  else
- t += stop_time.tv_usec - start_time.tv_usec;
+ t += (stop_time.tv_nsec - start_time.tv_nsec)/NSEC_PER_USEC;
  if (t == 0) {
  snd_printk(KERN_ERR "?? calculation error..\n");
  } else {

Patch

diff --git a/sound/pci/es1968.c b/sound/pci/es1968.c
index b0e3d92..6830c31 100644
--- a/sound/pci/es1968.c
+++ b/sound/pci/es1968.c
@@ -1710,7 +1710,7 @@  static void es1968_measure_clock(struct es1968 *chip)
  int i, apu;
  unsigned int pa, offset, t;
  struct esm_memory *memory;
- struct timeval start_time, stop_time;
+ struct timespec start_time, stop_time;

  if (chip->clock == 0)
  chip->clock = 48000; /* default clock value */
@@ -1759,12 +1759,12 @@  static void es1968_measure_clock(struct es1968
*chip)
  snd_es1968_bob_inc(chip, ESM_BOB_FREQ);
  __apu_set_register(chip, apu, 5, pa & 0xffff);
  snd_es1968_trigger_apu(chip, apu, ESM_APU_16BITLINEAR);
- do_gettimeofday(&start_time);
+ ktime_get_ts(&start_time);
  spin_unlock_irq(&chip->reg_lock);
  msleep(50);
  spin_lock_irq(&chip->reg_lock);
  offset = __apu_get_register(chip, apu, 5);
- do_gettimeofday(&stop_time);
+ ktime_get_ts(&stop_time);
  snd_es1968_trigger_apu(chip, apu, 0); /* stop */
  snd_es1968_bob_dec(chip);