CRAS: alsa-plugin - remove snd_pcm_cras_delay

PCM functions became thread-safe in 1.1.2. Some functions like
snd_pcm_delay and snd_pcm_sw_params_current will hold a lock.
snd_pcm_cras_delay is called by snd_pcm_delay, but
snd_pcm_cras_delay calls snd_pcm_sw_params_current. This causes
a deadlock.

There are several options that are not good:
(1) Define --disable-thread-safety in alsa-lib. This will be
    inconsistent with upstream alsa-lib.
(2) Set snd_pcm_t.need_lock=0. need_lock is in pcm_local.h
    and it's not easy to build with it. Also, need_lock means
    the plugin is thread safe and doesn't need locking in
    alsa-lib. Our plugin is not thread safe.
(3) Not to call snd_pcm_sw_params_current in snd_pcm_cras_delay.
    Calling snd_pcm_sw_params_current in .start introduces a
    similar deadlock. Also it's more accurate to get the latest
    boundary in .delay.
I don't see a good solution. Let's remove snd_pcm_cras_delay.

BUG=chromium:779936
TEST=Run loopback_latency -n 4000 and it does not hang.

Change-Id: I69b143aee2e95f8ef8f1a2c0f1604064255d0017
Reviewed-on: https://chromium-review.googlesource.com/758796
Commit-Ready: Wu-Cheng Li <wuchengli@chromium.org>
Tested-by: Wu-Cheng Li <wuchengli@chromium.org>
Reviewed-by: Cheng-Yi Chiang <cychiang@chromium.org>
Reviewed-by: Dylan Reid <dgreid@chromium.org>

1 files changed, 0 insertions, 86 deletions

diff --git a/cras/src/alsa_plugin/pcm_cras.c b/cras/src/alsa_plugin/pcm_cras.c
index 93b61a31..5591a115 100644
--- a/cras/src/alsa_plugin/pcm_cras.c
+++ b/cras/src/alsa_plugin/pcm_cras.c
@@ -228,29 +228,6 @@ static int snd_pcm_cras_prepare(snd_pcm_ioplug_t *io)
 	return cras_client_connect(pcm_cras->client);
 }
 
-/* Get the pcm boundary value. */
-static int get_boundary(snd_pcm_t *pcm, snd_pcm_uframes_t *boundary)
-{
-	snd_pcm_sw_params_t *sw_params;
-	int rc;
-
-	snd_pcm_sw_params_alloca(&sw_params);
-
-	rc = snd_pcm_sw_params_current(pcm, sw_params);
-	if (rc < 0) {
-		fprintf(stderr, "sw_params_current: %s\n", snd_strerror(rc));
-		return rc;
-	}
-
-	rc = snd_pcm_sw_params_get_boundary(sw_params, boundary);
-	if (rc < 0) {
-		fprintf(stderr, "get_boundary: %s\n", snd_strerror(rc));
-		return rc;
-	}
-
-	return 0;
-}
-
 /* Called when an ALSA stream is started. */
 static int snd_pcm_cras_start(snd_pcm_ioplug_t *io)
 {
@@ -300,71 +277,8 @@ error_out:
 	return rc;
 }
 
-static int snd_pcm_cras_delay(snd_pcm_ioplug_t *io, snd_pcm_sframes_t *delayp)
-{
-	snd_pcm_uframes_t limit;
-	int rc;
-	struct snd_pcm_cras *pcm_cras;
-	struct timespec latency;
-
-	pcm_cras = (struct snd_pcm_cras *)io->private_data;
-
-	rc = get_boundary(io->pcm, &limit);
-	if ((rc < 0) || (limit == 0)) {
-		*delayp = 0;
-		return -EINVAL;
-	}
-
-	/* To get the delay, first calculate the latency between now and the
-	 * playback/capture sample time for the old hw_ptr we tracked, note that
-	 * for playback path this latency could be negative. Then add it up with
-	 * the difference between appl_ptr and the old hw_ptr.
-	 */
-	if (io->stream == SND_PCM_STREAM_PLAYBACK) {
-		/* Do not compute latency if playback_sample_time is not set */
-		if (pcm_cras->playback_sample_time.tv_sec == 0 &&
-		    pcm_cras->playback_sample_time.tv_nsec == 0) {
-			latency.tv_sec = 0;
-			latency.tv_nsec = 0;
-		} else {
-			cras_client_calc_playback_latency(
-					&pcm_cras->playback_sample_time,
-					&latency);
-		}
-
-		*delayp = limit +
-			  io->appl_ptr -
-			  pcm_cras->playback_sample_index +
-			  latency.tv_sec * io->rate +
-			  latency.tv_nsec / (1000000000L / (long)io->rate);
-	} else {
-		/* Do not compute latency if capture_sample_time is not set */
-		if (pcm_cras->capture_sample_time.tv_sec == 0 &&
-		    pcm_cras->capture_sample_time.tv_nsec == 0) {
-			latency.tv_sec = 0;
-			latency.tv_nsec = 0;
-		} else {
-			cras_client_calc_capture_latency(
-					&pcm_cras->capture_sample_time,
-					&latency);
-		}
-
-		*delayp = limit +
-			  pcm_cras->capture_sample_index -
-			  io->appl_ptr +
-			  latency.tv_sec * io->rate +
-			  latency.tv_nsec / (1000000000L / (long)io->rate);
-	}
-
-	/* Both appl and hw pointers wrap at the pcm boundary. */
-	*delayp %= limit;
-
-	return 0;
-}
-
 static snd_pcm_ioplug_callback_t cras_pcm_callback = {
 	.close = snd_pcm_cras_close,
-	.delay = snd_pcm_cras_delay,
 	.start = snd_pcm_cras_start,
 	.stop = snd_pcm_cras_stop,
 	.pointer = snd_pcm_cras_pointer,