From 6047814d2bdda181c34f33a44befca46ee9f1b0f Mon Sep 17 00:00:00 2001
From: Xing Zheng <zhengxing@rock-chips.com>
Date: Wed, 10 Apr 2024 22:34:47 +0800
Subject: [PATCH] LOCAL: pcm: add the setting of SND_PCM_FORCE_ALIGN_FRAME via
 plugin or ENV

Some plugins (especially capture) cannot obtain a stable
period size and require PCM to obtain the avail phase for
forced synchronization, so that the plugin passed to
post-processing has a fixed size.

Note: If the algorithm in the plug-in needs to specify a fixed
frame size, the uncertain length in the recording 'ACCESS_MMAP'
mode will make the situation very troublesome, so here the frame
size is forced to be aligned and fixed according to the flag
'SND_PCM_FORCE_ALIGN_FRAME' specified by the plug-in.

Signed-off-by: Xing Zheng <zhengxing@rock-chips.com>
---
 include/pcm.h         |  2 ++
 src/pcm/pcm.c         | 46 ++++++++++++++++++++++++++++++++-----------
 src/pcm/pcm_extplug.c |  4 ++++
 src/pcm/pcm_plugin.c  | 15 ++++++++++++++
 4 files changed, 56 insertions(+), 11 deletions(-)

diff --git a/include/pcm.h b/include/pcm.h
index 102ff81..0c78ff4 100644
--- a/include/pcm.h
+++ b/include/pcm.h
@@ -413,6 +413,8 @@ typedef long snd_pcm_sframes_t;
 #define SND_PCM_NO_AUTO_FORMAT		0x00040000
 /** Disable soft volume control */
 #define SND_PCM_NO_SOFTVOL		0x00080000
+/** Force align frame size */
+#define SND_PCM_FORCE_ALIGN_FRAME	0x00100000
 
 /** PCM handle */
 typedef struct _snd_pcm snd_pcm_t;
diff --git a/src/pcm/pcm.c b/src/pcm/pcm.c
index 0a8cd0d..cedb3e5 100644
--- a/src/pcm/pcm.c
+++ b/src/pcm/pcm.c
@@ -7805,19 +7805,43 @@ snd_pcm_sframes_t snd_pcm_read_areas(snd_pcm_t *pcm, const snd_pcm_channel_area_
 			err = avail;
 			goto _end;
 		}
-		if (avail == 0) {
-			if (state == SND_PCM_STATE_DRAINING)
-				goto _end;
-			if (pcm->mode & SND_PCM_NONBLOCK) {
-				err = -EAGAIN;
-				goto _end;
+		if (pcm->mode & SND_PCM_FORCE_ALIGN_FRAME) {
+			if (state == SND_PCM_STATE_RUNNING &&
+				size > (snd_pcm_uframes_t)avail) {
+				if (snd_pcm_may_wait_for_avail_min(pcm, avail)) {
+					if (pcm->mode & SND_PCM_NONBLOCK) {
+						err = -EAGAIN;
+						goto _end;
+					}
+
+					err = snd_pcm_wait_nocheck(pcm, SND_PCM_WAIT_IO);
+					if (err < 0)
+						break;
+					goto _again;
+				}
+				/* the snd_pcm_may_wait_for_avail_min may check against the
+				 * updated hw.ptr (slaves), get the avail again here
+				 */
+				avail = __snd_pcm_avail_update(pcm);
+				if (avail < 0) {
+					err = avail;
+					goto _end;
+				}
 			}
+		} else {
+			if (avail == 0) {
+				if (state == SND_PCM_STATE_DRAINING)
+					goto _end;
+				if (pcm->mode & SND_PCM_NONBLOCK) {
+					err = -EAGAIN;
+					goto _end;
+				}
 
-			err = __snd_pcm_wait_in_lock(pcm, SND_PCM_WAIT_IO);
-			if (err < 0)
-				break;
-			goto _again;
-			
+				err = __snd_pcm_wait_in_lock(pcm, SND_PCM_WAIT_IO);
+				if (err < 0)
+					break;
+				goto _again;
+			}
 		}
 		frames = size;
 		if (frames > (snd_pcm_uframes_t) avail)
diff --git a/src/pcm/pcm_extplug.c b/src/pcm/pcm_extplug.c
index feb32b9..919e660 100644
--- a/src/pcm/pcm_extplug.c
+++ b/src/pcm/pcm_extplug.c
@@ -681,6 +681,7 @@ int snd_pcm_extplug_create(snd_pcm_extplug_t *extplug, const char *name,
 	int err;
 	snd_pcm_t *spcm, *pcm;
 	snd_config_t *sconf;
+	char *env_str = getenv("ALSA_EXTPLUG_FORCE_ALIGN_FRAME");
 
 	assert(root);
 	assert(extplug && extplug->callback);
@@ -720,6 +721,9 @@ int snd_pcm_extplug_create(snd_pcm_extplug_t *extplug, const char *name,
 	if (extplug->version >= 0x010001 && extplug->callback->init)
 		ext->plug.init = snd_pcm_extplug_init;
 
+	if (env_str && (strcasecmp(env_str, "true") == 0))
+		mode |= SND_PCM_FORCE_ALIGN_FRAME;
+
 	err = snd_pcm_new(&pcm, SND_PCM_TYPE_EXTPLUG, name, stream, mode);
 	if (err < 0) {
 		free(ext);
diff --git a/src/pcm/pcm_plugin.c b/src/pcm/pcm_plugin.c
index 9d7e233..8580284 100644
--- a/src/pcm/pcm_plugin.c
+++ b/src/pcm/pcm_plugin.c
@@ -485,6 +485,21 @@ snd_pcm_plugin_sync_hw_ptr_capture(snd_pcm_t *pcm,
 		 * there is more data available.
 		 */
 		slave_size = snd_pcm_avail_update(slave);
+
+		/**
+		 * NOTE: If the algorithm in the plug-in needs to specify a fixed
+		 * frame size, the uncertain length in the recording 'ACCESS_MMAP'
+		 * mode will make the situation very troublesome, so here the frame
+		 * size is forced to be aligned and fixed according to the flag
+		 * 'SND_PCM_FORCE_ALIGN_FRAME' specified by the plug-in.
+		 */
+		if (pcm->mode & SND_PCM_FORCE_ALIGN_FRAME) {
+			if (slave_size < pcm->period_size)
+				continue;
+			if (slave_size > pcm->period_size)
+				slave_size = pcm->period_size;
+		}
+
 		result = snd_pcm_mmap_begin(slave, &slave_areas, &slave_offset, &slave_frames);
 		if (result < 0) {
 			err = result;
-- 
2.34.1