[alsa-devel] [PATCH v2 2/6] pcm: dshare: Added "hw_ptr_alignment" option in configuration for alignment of slave pointers

[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 dshare 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 dshare 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_dshare.c | 40 +++++++++++++++++++++++++++++++++++-----
 1 file changed, 35 insertions(+), 5 deletions(-)

diff --git a/src/pcm/pcm_dshare.c b/src/pcm/pcm_dshare.c
index f135b5d..cf8a863 100644
--- a/src/pcm/pcm_dshare.c
+++ b/src/pcm/pcm_dshare.c
@@ -333,16 +333,16 @@ 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;
 }
 
-static int snd_pcm_dshare_start_timer(snd_pcm_direct_t *dshare)
+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)
 		return err;
@@ -364,7 +364,8 @@ static int snd_pcm_dshare_start(snd_pcm_t *pcm)
 	else if (avail < 0)
 		return 0;
 	else {
-		if ((err = snd_pcm_dshare_start_timer(dshare)) < 0)
+		err = snd_pcm_dshare_start_timer(pcm, dshare);
+		if (err < 0)
 			return err;
 		snd_pcm_dshare_sync_area(pcm);
 	}
@@ -547,7 +548,8 @@ static snd_pcm_sframes_t snd_pcm_dshare_mmap_commit(snd_pcm_t *pcm,
 		return 0;
 	snd_pcm_mmap_appl_forward(pcm, size);
 	if (dshare->state == STATE_RUN_PENDING) {
-		if ((err = snd_pcm_dshare_start_timer(dshare)) < 0)
+		err = snd_pcm_dshare_start_timer(pcm, dshare);
+		if (err < 0)
 			return err;
 	} else if (dshare->state == SND_PCM_STATE_RUNNING ||
 		   dshare->state == SND_PCM_STATE_DRAINING) {
@@ -755,6 +757,7 @@ int snd_pcm_dshare_open(snd_pcm_t **pcmp, const char *name,
 	dshare->slowptr = opts->slowptr;
 	dshare->max_periods = opts->max_periods;
 	dshare->var_periodsize = opts->var_periodsize;
+	dshare->hw_ptr_alignment = opts->hw_ptr_alignment;
 	dshare->sync_ptr = snd_pcm_dshare_sync_ptr;
 
  retry:
@@ -912,6 +915,12 @@ 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
@@ -936,6 +945,27 @@ 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 under 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. Such wakeup delay could otherwise end up with Xruns in
+  case of a dependency to another sound device (e.g. forwarding of
+  microphone to speaker). Else "no" will be chosen.
+
 \subsection pcm_plugins_dshare_funcref Function reference
 
 <UL>
-- 
2.7.4