ALSA: Provide a CLOCK_MONOTONIC_RAW timestamp type

For applications which need to synchronise with external timebases such
as broadcast TV applications the kernel monotonic time is not optimal as
it includes adjustments from NTP and so may still include discontinuities
due to that. A raw monotonic time which does not include any adjustments
is available in the kernel from getrawmonotonic() so provide userspace with
a new timestamp type SNDRV_PCM_TSTAMP_TYPE_MONOTONIC_RAW which provides
timestamps based on this as an option.

[dropped tstamp_type assignment code, as it's no longer needed -- tiwai]
Reported-by: Daniel Thompson <daniel.thompson@linaro.org>
Signed-off-by: Mark Brown <broonie@linaro.org>
Acked-by: Jaroslav Kysela <perex@perex.cz>
Signed-off-by: Takashi Iwai <tiwai@suse.de>

include/sound/pcm.h

@@ -931,10 +931,17 @@ void snd_pcm_timer_done(struct snd_pcm_substream *substream);
 static inline void snd_pcm_gettime(struct snd_pcm_runtime *runtime,
 				   struct timespec *tv)
 {
-	if (runtime->tstamp_type == SNDRV_PCM_TSTAMP_TYPE_MONOTONIC)
+	switch (runtime->tstamp_type) {
+	case SNDRV_PCM_TSTAMP_TYPE_MONOTONIC:
 		ktime_get_ts(tv);
-	else
+		break;
+	case SNDRV_PCM_TSTAMP_TYPE_MONOTONIC_RAW:
+		getrawmonotonic(tv);
+		break;
+	default:
 		getnstimeofday(tv);
+		break;
+	}
 }
 
 /*

include/uapi/sound/asound.h

@@ -462,7 +462,8 @@ struct snd_xfern {
 enum {
 	SNDRV_PCM_TSTAMP_TYPE_GETTIMEOFDAY = 0,	/* gettimeofday equivalent */
 	SNDRV_PCM_TSTAMP_TYPE_MONOTONIC,	/* posix_clock_monotonic equivalent */
-	SNDRV_PCM_TSTAMP_TYPE_LAST = SNDRV_PCM_TSTAMP_TYPE_MONOTONIC,
+	SNDRV_PCM_TSTAMP_TYPE_MONOTONIC_RAW,    /* monotonic_raw (no NTP) */
+	SNDRV_PCM_TSTAMP_TYPE_LAST = SNDRV_PCM_TSTAMP_TYPE_MONOTONIC_RAW,
 };
 
 /* channel positions */