[ALSA] Use posix clock monotonic for PCM and timer timestamps

We need an accurate and continuous (monotonic) time sources to do
accurate synchronization among more timing sources. This patch allows
to enable monotonic timestamps for ALSA PCM devices and enables monotonic
timestamps for ALSA timer devices.

Signed-off-by: Jaroslav Kysela <perex@perex.cz>

1 files changed, 13 insertions, 3 deletions

diff --git a/sound/core/timer.c b/sound/core/timer.c
index e7dc56ca4b97..7e5fe2d91662 100644
--- a/sound/core/timer.c
+++ b/sound/core/timer.c
@@ -44,11 +44,14 @@
 #endif
 
 static int timer_limit = DEFAULT_TIMER_LIMIT;
+static int timer_tstamp_monotonic = 1;
 MODULE_AUTHOR("Jaroslav Kysela <perex@perex.cz>, Takashi Iwai <tiwai@suse.de>");
 MODULE_DESCRIPTION("ALSA timer interface");
 MODULE_LICENSE("GPL");
 module_param(timer_limit, int, 0444);
 MODULE_PARM_DESC(timer_limit, "Maximum global timers in system.");
+module_param(timer_tstamp_monotonic, int, 0444);
+MODULE_PARM_DESC(timer_tstamp_monotonic, "Use posix monotonic clock source for timestamps (default).");
 
 struct snd_timer_user {
         struct snd_timer_instance *timeri;
@@ -381,7 +384,10 @@ static void snd_timer_notify1(struct snd_timer_instance *ti, int event)
         struct snd_timer_instance *ts;
         struct timespec tstamp;
 
-        getnstimeofday(&tstamp);
+        if (timer_tstamp_monotonic)
+                do_posix_clock_monotonic_gettime(&tstamp);
+        else
+                getnstimeofday(&tstamp);
         snd_assert(event >= SNDRV_TIMER_EVENT_START &&
                    event <= SNDRV_TIMER_EVENT_PAUSE, return);
         if (event == SNDRV_TIMER_EVENT_START ||
@@ -1182,8 +1188,12 @@ static void snd_timer_user_tinterrupt(struct snd_timer_instance *timeri,
                 spin_unlock(&tu->qlock);
                 return;
         }
-        if (tu->last_resolution != resolution || ticks > 0)
-                getnstimeofday(&tstamp);
+        if (tu->last_resolution != resolution || ticks > 0) {
+                if (timer_tstamp_monotonic)
+                        do_posix_clock_monotonic_gettime(&tstamp);
+                else
+                        getnstimeofday(&tstamp);
+        }
         if ((tu->filter & (1 << SNDRV_TIMER_EVENT_RESOLUTION)) &&
             tu->last_resolution != resolution) {
                 r1.event = SNDRV_TIMER_EVENT_RESOLUTION;