ALSA: aloop: using raw cycles and jiffies

The system tick may be modified by NTP when we connect
with network, then  jiffies have an offset compared to
the local clock, it will cause the irq_pos / delta_play /
delta_capt also be inaccurate.

Therefore, we need a way to get raw jiffies which follows
local raw clocks.

Change-Id: I9be1790dfd98e430982dad6f03b04532889279a6
Signed-off-by: Xing Zheng <zhengxing@rock-chips.com>

1 files changed, 24 insertions, 5 deletions

diff --git a/sound/drivers/aloop.c b/sound/drivers/aloop.c
index 847f70348d4d..bdbd3882d2de 100644
--- a/sound/drivers/aloop.c
+++ b/sound/drivers/aloop.c
@@ -50,12 +50,15 @@ MODULE_SUPPORTED_DEVICE("{{ALSA,Loopback soundcard}}");
 
 #define MAX_PCM_SUBSTREAMS	8
 
+static bool use_raw_jiffies;
 static int index[SNDRV_CARDS] = SNDRV_DEFAULT_IDX;	/* Index 0-MAX */
 static char *id[SNDRV_CARDS] = SNDRV_DEFAULT_STR;	/* ID for this card */
 static bool enable[SNDRV_CARDS] = {1, [1 ... (SNDRV_CARDS - 1)] = 0};
 static int pcm_substreams[SNDRV_CARDS] = {[0 ... (SNDRV_CARDS - 1)] = 8};
 static int pcm_notify[SNDRV_CARDS];
 
+module_param(use_raw_jiffies, bool, 0444);
+MODULE_PARM_DESC(use_raw_jiffies, "Use raw jiffies follows local clocks.");
 module_param_array(index, int, NULL, 0444);
 MODULE_PARM_DESC(index, "Index value for loopback soundcard.");
 module_param_array(id, charp, NULL, 0444);
@@ -125,6 +128,22 @@ struct loopback_pcm {
 
 static struct platform_device *devices[SNDRV_CARDS];
 
+static inline unsigned long get_raw_jiffies(void)
+{
+	struct timespec64 ts64;
+
+	getrawmonotonic64(&ts64);
+	return timespec64_to_jiffies(&ts64);
+}
+
+static inline unsigned long cycles_to_jiffies(void)
+{
+	if (likely(use_raw_jiffies))
+		return get_raw_jiffies();
+
+	return jiffies;
+}
+
 static inline unsigned int byte_pos(struct loopback_pcm *dpcm, unsigned int x)
 {
 	if (dpcm->pcm_rate_shift == NO_PITCH) {
@@ -270,7 +289,7 @@ static int loopback_trigger(struct snd_pcm_substream *substream, int cmd)
 		err = loopback_check_format(cable, substream->stream);
 		if (err < 0)
 			return err;
-		dpcm->last_jiffies = jiffies;
+		dpcm->last_jiffies = cycles_to_jiffies();
 		dpcm->pcm_rate_shift = 0;
 		dpcm->last_drift = 0;
 		spin_lock(&cable->lock);	
@@ -302,7 +321,7 @@ static int loopback_trigger(struct snd_pcm_substream *substream, int cmd)
 	case SNDRV_PCM_TRIGGER_PAUSE_RELEASE:
 	case SNDRV_PCM_TRIGGER_RESUME:
 		spin_lock(&cable->lock);
-		dpcm->last_jiffies = jiffies;
+		dpcm->last_jiffies = cycles_to_jiffies();
 		cable->pause &= ~stream;
 		loopback_timer_start(dpcm);
 		spin_unlock(&cable->lock);
@@ -482,12 +501,12 @@ static unsigned int loopback_pos_update(struct loopback_cable *cable)
 
 	running = cable->running ^ cable->pause;
 	if (running & (1 << SNDRV_PCM_STREAM_PLAYBACK)) {
-		delta_play = jiffies - dpcm_play->last_jiffies;
+		delta_play = cycles_to_jiffies() - dpcm_play->last_jiffies;
 		dpcm_play->last_jiffies += delta_play;
 	}
 
 	if (running & (1 << SNDRV_PCM_STREAM_CAPTURE)) {
-		delta_capt = jiffies - dpcm_capt->last_jiffies;
+		delta_capt = cycles_to_jiffies() - dpcm_capt->last_jiffies;
 		dpcm_capt->last_jiffies += delta_capt;
 	}
 
@@ -1108,7 +1127,7 @@ static void print_dpcm_info(struct snd_info_buffer *buffer,
 	snd_iprintf(buffer, "    irq_pos:\t\t%u\n", dpcm->irq_pos);
 	snd_iprintf(buffer, "    period_frac:\t%u\n", dpcm->period_size_frac);
 	snd_iprintf(buffer, "    last_jiffies:\t%lu (%lu)\n",
-					dpcm->last_jiffies, jiffies);
+					dpcm->last_jiffies, cycles_to_jiffies());
 	snd_iprintf(buffer, "    timer_expires:\t%lu\n", dpcm->timer.expires);
 }