Allow user to provide extra PCM delay component

If everything fails, user will be able to adjust PCM delay. Additionally,
this feature will allow to specify different delay for every configured
(in the ALSA configuration file) Bluetooth device, as follows:

$ cat .asoundrc
pcm.device-1 {
	type bluealsa
	device "AB:CD:EF:01:23:45"
	profile "a2dp"
	delay 30000
}
pcm.device-2 {
	type bluealsa
	device "AB:CD:EF:45:67:89"
	profile "a2dp"
	delay 15000
}

README.md

@@ -60,6 +60,7 @@ like this:
 	defaults.bluealsa.interface "hci0"
 	defaults.bluealsa.device "XX:XX:XX:XX:XX:XX"
 	defaults.bluealsa.profile "a2dp"
+	defaults.bluealsa.delay 10000
 
 BlueALSA also allows to capture audio from the connected Bluetooth device. To do so, one has to
 use the capture PCM device, e.g.:
@@ -118,7 +119,7 @@ Troubleshooting
 
 	If connected Bluetooth headset supports AAC and BlueALSA was compiled with AAC (`./configure
 	--enable-aac`) such an encoder will be used for A2DP profile. However, AAC encoding is
-	buggious - sorry for that. If the encoded packet size exceeds writing MTU, fragmentation occurs,
+	buggy - sorry for that. If the encoded packet size exceeds writing MTU, fragmentation occurs,
 	which is not handled correctly. As a workaround, it is possible to decrease packet size by
 	degrading audio quality via the `--aac-vbr-mode=NB` option.
 

src/asound/20-bluealsa.conf

@@ -1,5 +1,9 @@
 # BlueALSA integration setup
 
+defaults.bluealsa.interface "hci0"
+defaults.bluealsa.profile "a2dp"
+defaults.bluealsa.delay 20000
+
 ctl.bluealsa {
 	@args [ HCI ]
 	@args.HCI {
@@ -14,7 +18,7 @@ ctl.bluealsa {
 }
 
 pcm.bluealsa {
-	@args [ HCI DEV PROFILE ]
+	@args [ HCI DEV PROFILE DELAY ]
 	@args.HCI {
 		type string
 		default {
@@ -36,12 +40,20 @@ pcm.bluealsa {
 			name defaults.bluealsa.profile
 		}
 	}
+	@args.DELAY {
+		type integer
+		default {
+			@func refer
+			name defaults.bluealsa.delay
+		}
+	}
 	type plug
 	slave.pcm {
 		type bluealsa
 		interface $HCI
 		device $DEV
 		profile $PROFILE
+		delay $DELAY
 	}
 	hint {
 		show {

src/asound/bluealsa-pcm.c

@@ -52,6 +52,8 @@ struct bluealsa_pcm {
 
 	/* communication and encoding/decoding delay */
 	snd_pcm_sframes_t delay;
+	/* user provided extra delay component */
+	snd_pcm_sframes_t delay_ex;
 
 	/* ALSA operates on frames, we on bytes */
 	size_t frame_size;
@@ -336,7 +338,7 @@ static int bluealsa_delay(snd_pcm_ioplug_t *io, snd_pcm_sframes_t *delayp) {
 
 	}
 
-	*delayp = delay + pcm->delay;
+	*delayp = delay + pcm->delay + pcm->delay_ex;
 	return 0;
 }
 
@@ -480,6 +482,7 @@ SND_PCM_PLUGIN_DEFINE_FUNC(bluealsa) {
 	const char *device = NULL;
 	const char *profile = NULL;
 	struct bluealsa_pcm *pcm;
+	long delay = 0;
 	int ret;
 
 	snd_config_for_each(i, next, conf) {
@@ -515,6 +518,13 @@ SND_PCM_PLUGIN_DEFINE_FUNC(bluealsa) {
 			}
 			continue;
 		}
+		if (strcmp(id, "delay") == 0) {
+			if (snd_config_get_integer(n, &delay) < 0) {
+				SNDERR("Invalid type for %s", id);
+				return -EINVAL;
+			}
+			continue;
+		}
 
 		SNDERR("Unknown field %s", id);
 		return -EINVAL;
@@ -541,6 +551,7 @@ SND_PCM_PLUGIN_DEFINE_FUNC(bluealsa) {
 	pcm->fd = -1;
 	pcm->event_fd = -1;
 	pcm->pcm_fd = -1;
+	pcm->delay_ex = delay;
 
 	if ((pcm->fd = bluealsa_open(interface)) == -1) {
 		SNDERR("BlueALSA connection failed: %s", strerror(errno));