ALSA: bcm2835: use a completion instead of a semaphore for sync

The kernel completion interface is a simple synchronization
mechanism that is preferable over semaphores to signal the
occurence of an event.

Semaphores are optimized for the non-contention case since
in most situations they will be available. But the wait for
completion is the opposite case since the code calling down
will wait on most cases.

So, is better to use the completion mechanism that has been
developed for this exact use case instead of semaphores.

Signed-off-by: Javier Martinez Canillas <[email protected]>

sound/arm/bcm2835-vchiq.c

@@ -27,6 +27,7 @@
 #include <linux/delay.h>
 #include <linux/atomic.h>
 #include <linux/module.h>
+#include <linux/completion.h>
 
 #include "bcm2835.h"
 
@@ -53,7 +54,7 @@
 typedef struct opaque_AUDIO_INSTANCE_T {
 	uint32_t num_connections;
 	VCHI_SERVICE_HANDLE_T vchi_handle[VCHI_MAX_NUM_CONNECTIONS];
-	struct semaphore msg_avail_event;
+	struct completion msg_avail_comp;
 	struct mutex vchi_mutex;
 	bcm2835_alsa_stream_t *alsa_stream;
 	int32_t result;
@@ -178,7 +179,7 @@ static void audio_vchi_callback(void *param,
 		    (" .. instance=%p, m.type=VC_AUDIO_MSG_TYPE_RESULT, success=%d\n",
 		     instance, m.u.result.success);
 		instance->result = m.u.result.success;
-		up(&instance->msg_avail_event);
+		complete(&instance->msg_avail_comp);
 	} else if (m.type == VC_AUDIO_MSG_TYPE_COMPLETE) {
 		irq_handler_t callback = (irq_handler_t) m.u.complete.callback;
 		LOG_DBG
@@ -435,8 +436,8 @@ static int bcm2835_audio_set_ctls_chan(bcm2835_alsa_stream_t * alsa_stream,
 	m.u.control.dest = chip->dest;
 	m.u.control.volume = chip->volume;
 
-	/* Create the message available event */
-	sema_init(&instance->msg_avail_event, 0);
+	/* Create the message available completion */
+	init_completion(&instance->msg_avail_comp);
 
 	/* Send the message to the videocore */
 	success = vchi_msg_queue(instance->vchi_handle[0],
@@ -452,11 +453,10 @@ static int bcm2835_audio_set_ctls_chan(bcm2835_alsa_stream_t * alsa_stream,
 	}
 
 	/* We are expecting a reply from the videocore */
-	if (down_interruptible(&instance->msg_avail_event)) {
+	ret = wait_for_completion_interruptible(&instance->msg_avail_comp);
+	if (ret) {
 		LOG_ERR("%s: failed on waiting for event (status=%d)\n",
 			__func__, success);
-
-		ret = -1;
 		goto unlock;
 	}
 
@@ -539,8 +539,8 @@ int bcm2835_audio_set_params(bcm2835_alsa_stream_t * alsa_stream,
 	m.u.config.samplerate = samplerate;
 	m.u.config.bps = bps;
 
-	/* Create the message available event */
-	sema_init(&instance->msg_avail_event, 0);
+	/* Create the message available completion */
+	init_completion(&instance->msg_avail_comp);
 
 	/* Send the message to the videocore */
 	success = vchi_msg_queue(instance->vchi_handle[0],
@@ -556,11 +556,10 @@ int bcm2835_audio_set_params(bcm2835_alsa_stream_t * alsa_stream,
 	}
 
 	/* We are expecting a reply from the videocore */
-	if (down_interruptible(&instance->msg_avail_event)) {
+	ret = wait_for_completion_interruptible(&instance->msg_avail_comp);
+	if (ret) {
 		LOG_ERR("%s: failed on waiting for event (status=%d)\n",
 			__func__, success);
-
-		ret = -1;
 		goto unlock;
 	}
 
@@ -688,8 +687,8 @@ int bcm2835_audio_close(bcm2835_alsa_stream_t * alsa_stream)
 
 	m.type = VC_AUDIO_MSG_TYPE_CLOSE;
 
-	/* Create the message available event */
-	sema_init(&instance->msg_avail_event, 0);
+	/* Create the message available completion */
+	init_completion(&instance->msg_avail_comp);
 
 	/* Send the message to the videocore */
 	success = vchi_msg_queue(instance->vchi_handle[0],
@@ -702,11 +701,11 @@ int bcm2835_audio_close(bcm2835_alsa_stream_t * alsa_stream)
 		ret = -1;
 		goto unlock;
 	}
-	if (down_interruptible(&instance->msg_avail_event)) {
+
+	ret = wait_for_completion_interruptible(&instance->msg_avail_comp);
+	if (ret) {
 		LOG_ERR("%s: failed on waiting for event (status=%d)",
 			__func__, success);
-
-		ret = -1;
 		goto unlock;
 	}
 	if (instance->result != 0) {