[alsa-devel] [PATCH v2 3/6] pcm: dsnoop: Added "hw_ptr_alignment" option in configuration for slave pointer alignment

[vanitha.channaiah at in.bosch.com]

From: Vanitha Channaiah <vanitha.channaiah at in.bosch.com>

This change adapt the fix commit 6b058fda9dce
("pcm: dmix: Add option to allow alignment of slave pointers")
for dsnoop plugin

Issue is that snd_pcm_wait() goes back to waiting because the hw_ptr
is not period aligned. Therefore snd_pcm_wait() will block for a longer
time as required.

With these rcar driver changes the exact position of the dma is returned.
During snd_pcm_start they read hw_ptr as reference, and this hw_ptr
is now not period aligned, and is a little ahead over the period while it
is read. Therefore when the avail is calculated during snd_pcm_wait(),
it is missing the avail_min by a few frames.

An additional option hw_ptr_alignment is provided to dsnoop configuration,
to allow the user to configure the slave application and hw pointer
alignment at startup

Signed-off-by: Vanitha Channaiah <vanitha.channaiah at in.bosch.com>
---
 src/pcm/pcm_direct.c |  1 -
 src/pcm/pcm_dmix.c   |  2 ++
 src/pcm/pcm_dshare.c |  2 ++
 src/pcm/pcm_dsnoop.c | 30 +++++++++++++++++++++++++++++-
 4 files changed, 33 insertions(+), 2 deletions(-)

diff --git a/src/pcm/pcm_direct.c b/src/pcm/pcm_direct.c
index 411a035..54d9900 100644
--- a/src/pcm/pcm_direct.c
+++ b/src/pcm/pcm_direct.c
@@ -2043,7 +2043,6 @@ int snd_pcm_direct_parse_open_conf(snd_config_t *root, snd_config_t *conf,
 
 void snd_pcm_direct_reset_slave_ptr(snd_pcm_t *pcm, snd_pcm_direct_t *dmix)
 {
-	dmix->slave_appl_ptr = dmix->slave_hw_ptr = *dmix->spcm->hw.ptr;
 
 	if (dmix->hw_ptr_alignment == SND_PCM_HW_PTR_ALIGNMENT_ROUNDUP ||
 		(dmix->hw_ptr_alignment == SND_PCM_HW_PTR_ALIGNMENT_AUTO &&
diff --git a/src/pcm/pcm_dmix.c b/src/pcm/pcm_dmix.c
index dcde40d..274726e 100644
--- a/src/pcm/pcm_dmix.c
+++ b/src/pcm/pcm_dmix.c
@@ -562,6 +562,7 @@ static int snd_pcm_dmix_reset(snd_pcm_t *pcm)
 	snd_pcm_direct_t *dmix = pcm->private_data;
 	dmix->hw_ptr %= pcm->period_size;
 	dmix->appl_ptr = dmix->last_appl_ptr = dmix->hw_ptr;
+	dmix->slave_appl_ptr = dmix->slave_hw_ptr = *dmix->spcm->hw.ptr;
 	snd_pcm_direct_reset_slave_ptr(pcm, dmix);
 	return 0;
 }
@@ -571,6 +572,7 @@ static int snd_pcm_dmix_start_timer(snd_pcm_t *pcm, snd_pcm_direct_t *dmix)
 	int err;
 
 	snd_pcm_hwsync(dmix->spcm);
+	dmix->slave_appl_ptr = dmix->slave_hw_ptr = *dmix->spcm->hw.ptr;
 	snd_pcm_direct_reset_slave_ptr(pcm, dmix);
 	err = snd_timer_start(dmix->timer);
 	if (err < 0)
diff --git a/src/pcm/pcm_dshare.c b/src/pcm/pcm_dshare.c
index cf8a863..b75809c 100644
--- a/src/pcm/pcm_dshare.c
+++ b/src/pcm/pcm_dshare.c
@@ -333,6 +333,7 @@ static int snd_pcm_dshare_reset(snd_pcm_t *pcm)
 	snd_pcm_direct_t *dshare = pcm->private_data;
 	dshare->hw_ptr %= pcm->period_size;
 	dshare->appl_ptr = dshare->last_appl_ptr = dshare->hw_ptr;
+	dshare->slave_appl_ptr = dshare->slave_hw_ptr = *dshare->spcm->hw.ptr;
 	snd_pcm_direct_reset_slave_ptr(pcm, dshare);
 	return 0;
 }
@@ -342,6 +343,7 @@ static int snd_pcm_dshare_start_timer(snd_pcm_t *pcm, snd_pcm_direct_t *dshare)
 	int err;
 
 	snd_pcm_hwsync(dshare->spcm);
+	dshare->slave_appl_ptr = dshare->slave_hw_ptr = *dshare->spcm->hw.ptr;
 	snd_pcm_direct_reset_slave_ptr(pcm, dshare);
 	err = snd_timer_start(dshare->timer);
 	if (err < 0)
diff --git a/src/pcm/pcm_dsnoop.c b/src/pcm/pcm_dsnoop.c
index d08b624..58b1e53 100644
--- a/src/pcm/pcm_dsnoop.c
+++ b/src/pcm/pcm_dsnoop.c
@@ -278,6 +278,7 @@ static int snd_pcm_dsnoop_reset(snd_pcm_t *pcm)
 	dsnoop->hw_ptr %= pcm->period_size;
 	dsnoop->appl_ptr = dsnoop->hw_ptr;
 	dsnoop->slave_appl_ptr = dsnoop->slave_hw_ptr;
+	snd_pcm_direct_reset_slave_ptr(pcm, dsnoop);
 	return 0;
 }
 
@@ -285,12 +286,13 @@ static int snd_pcm_dsnoop_start(snd_pcm_t *pcm)
 {
 	snd_pcm_direct_t *dsnoop = pcm->private_data;
 	int err;
-	
+
 	if (dsnoop->state != SND_PCM_STATE_PREPARED)
 		return -EBADFD;
 	snd_pcm_hwsync(dsnoop->spcm);
 	snoop_timestamp(pcm);
 	dsnoop->slave_appl_ptr = dsnoop->slave_hw_ptr;
+	snd_pcm_direct_reset_slave_ptr(pcm, dsnoop);
 	err = snd_timer_start(dsnoop->timer);
 	if (err < 0)
 		return err;
@@ -627,6 +629,7 @@ int snd_pcm_dsnoop_open(snd_pcm_t **pcmp, const char *name,
 	dsnoop->max_periods = opts->max_periods;
 	dsnoop->var_periodsize = opts->var_periodsize;
 	dsnoop->sync_ptr = snd_pcm_dsnoop_sync_ptr;
+	dsnoop->hw_ptr_alignment = opts->hw_ptr_alignment;
 
  retry:
 	if (first_instance) {
@@ -771,6 +774,12 @@ pcm.name {
 	ipc_key INT		# unique IPC key
 	ipc_key_add_uid BOOL	# add current uid to unique IPC key
 	ipc_perm INT		# IPC permissions (octal, default 0600)
+	hw_ptr_alignment STR	# Slave application and hw pointer alignment type
+		# STR can be one of the below strings :
+		# no
+		# roundup
+		# rounddown
+		# auto (default)
 	slave STR
 	# or
 	slave {			# Slave definition
@@ -795,6 +804,25 @@ pcm.name {
 }
 \endcode
 
+<code>hw_ptr_alignment</code> specifies slave application and hw
+pointer alignment type. By default hw_ptr_alignment is auto. Below are
+the possible configurations:
+- no: minimal latency with minimal frames dropped at startup. But
+  wakeup of application (return from snd_pcm_wait() or poll()) can
+  take up to 2 * period.
+- roundup: It is guaranteed that all frames will be played at
+  startup. But the latency will increase upto period-1 frames.
+- rounddown: It is guaranteed that a wakeup will happen for each
+  period and frames can be written from application. But on startup
+  upto period-1 frames will be dropped.
+- auto: Selects the best approach depending on the used period and
+  buffer size.
+  If the application buffer size is < 2 * application period,
+  "roundup" will be selected to avoid over runs. If the slave_period
+  is < 10ms we could expect that there are low latency
+  requirements. Therefore "rounddown" will be chosen to avoid long
+  wakeup times. Else "no" will be chosen.
+
 \subsection pcm_plugins_dsnoop_funcref Function reference
 
 <UL>
-- 
2.7.4