staging: bcm2835-audio: Operate non-atomic PCM ops

This is the most significant part in the patch series.

The bcm2835-audio driver used to queue the commands to vc04 core via
workqueue, but basically the whole accesses to vc04 core are done in
the sleepable context, including the callback calls.  In such a case,
rewriting the code using non-atomic PCM ops will simplify the logic a
lot.

This patch does it: all workqueue are gone and each former-work
implementation is now directly called from PCM ops like trigger and
write transfer.

Along with it, the DMA position updater, bcm2835_playback_fifo(), was
also rewritten to use a simpler logic.  Now it handles the XRUN and
draining properly by calling snd_pcm_stop() conditionally.

The current position is kept in atomic_t value so that it can be read
concurrently from the pointer callback.

Also, the bcm2835_audio_instance object is allocated at the beginning
of bcm2835_audio_open().  This makes the resource management clearer.

Signed-off-by: Takashi Iwai <tiwai@suse.de>
Tested-by: Stefan Wahren <stefan.wahren@i2se.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/vc04_services/bcm2835-audio/bcm2835-pcm.c

@@ -11,7 +11,8 @@
 /* hardware definition */
 static const struct snd_pcm_hardware snd_bcm2835_playback_hw = {
 	.info = (SNDRV_PCM_INFO_INTERLEAVED | SNDRV_PCM_INFO_BLOCK_TRANSFER |
-	SNDRV_PCM_INFO_MMAP | SNDRV_PCM_INFO_MMAP_VALID),
+		 SNDRV_PCM_INFO_MMAP | SNDRV_PCM_INFO_MMAP_VALID |
+		 SNDRV_PCM_INFO_DRAIN_TRIGGER),
 	.formats = SNDRV_PCM_FMTBIT_U8 | SNDRV_PCM_FMTBIT_S16_LE,
 	.rates = SNDRV_PCM_RATE_CONTINUOUS | SNDRV_PCM_RATE_8000_48000,
 	.rate_min = 8000,
@@ -27,7 +28,8 @@ static const struct snd_pcm_hardware snd_bcm2835_playback_hw = {
 
 static const struct snd_pcm_hardware snd_bcm2835_playback_spdif_hw = {
 	.info = (SNDRV_PCM_INFO_INTERLEAVED | SNDRV_PCM_INFO_BLOCK_TRANSFER |
-	SNDRV_PCM_INFO_MMAP | SNDRV_PCM_INFO_MMAP_VALID),
+		 SNDRV_PCM_INFO_MMAP | SNDRV_PCM_INFO_MMAP_VALID |
+		 SNDRV_PCM_INFO_DRAIN_TRIGGER),
 	.formats = SNDRV_PCM_FMTBIT_S16_LE,
 	.rates = SNDRV_PCM_RATE_CONTINUOUS | SNDRV_PCM_RATE_44100 |
 	SNDRV_PCM_RATE_48000,
@@ -47,42 +49,34 @@ static void snd_bcm2835_playback_free(struct snd_pcm_runtime *runtime)
 	kfree(runtime->private_data);
 }
 
-void bcm2835_playback_fifo(struct bcm2835_alsa_stream *alsa_stream)
+void bcm2835_playback_fifo(struct bcm2835_alsa_stream *alsa_stream,
+			   unsigned int bytes)
 {
-	unsigned int consumed = 0;
-	int new_period = 0;
-
-	audio_info("alsa_stream=%p substream=%p\n", alsa_stream,
-		alsa_stream ? alsa_stream->substream : 0);
-
-	consumed = bcm2835_audio_retrieve_buffers(alsa_stream);
-
-	/* We get called only if playback was triggered, So, the number of buffers we retrieve in
-	 * each iteration are the buffers that have been played out already
-	 */
-
-	if (alsa_stream->period_size) {
-		if ((alsa_stream->pos / alsa_stream->period_size) !=
-			((alsa_stream->pos + consumed) / alsa_stream->period_size))
-			new_period = 1;
-	}
-	audio_debug("updating pos cur: %d + %d max:%d period_bytes:%d, hw_ptr: %d new_period:%d\n",
-		alsa_stream->pos,
-		consumed,
-		alsa_stream->buffer_size,
-		(int) (alsa_stream->period_size * alsa_stream->substream->runtime->periods),
-		frames_to_bytes(alsa_stream->substream->runtime, alsa_stream->substream->runtime->status->hw_ptr),
-		new_period);
-	if (alsa_stream->buffer_size) {
-		alsa_stream->pos += consumed & ~(1 << 30);
-		alsa_stream->pos %= alsa_stream->buffer_size;
+	struct snd_pcm_substream *substream = alsa_stream->substream;
+	unsigned int pos;
+
+	if (!alsa_stream->period_size)
+		return;
+
+	if (bytes >= alsa_stream->buffer_size) {
+		snd_pcm_stream_lock(substream);
+		snd_pcm_stop(substream,
+			     alsa_stream->draining ?
+			     SNDRV_PCM_STATE_SETUP :
+			     SNDRV_PCM_STATE_XRUN);
+		snd_pcm_stream_unlock(substream);
+		return;
 	}
 
-	if (alsa_stream->substream) {
-		if (new_period)
-			snd_pcm_period_elapsed(alsa_stream->substream);
-	} else {
-		audio_warning(" unexpected NULL substream\n");
+	pos = atomic_read(&alsa_stream->pos);
+	pos += bytes;
+	pos %= alsa_stream->buffer_size;
+	atomic_set(&alsa_stream->pos, pos);
+
+	alsa_stream->period_offset += bytes;
+	if (alsa_stream->period_offset >= alsa_stream->period_size) {
+		alsa_stream->period_offset %= alsa_stream->period_size;
+		snd_pcm_period_elapsed(substream);
 	}
 }
 
@@ -246,7 +240,8 @@ static int snd_bcm2835_pcm_prepare(struct snd_pcm_substream *substream)
 
 	alsa_stream->buffer_size = snd_pcm_lib_buffer_bytes(substream);
 	alsa_stream->period_size = snd_pcm_lib_period_bytes(substream);
-	alsa_stream->pos = 0;
+	atomic_set(&alsa_stream->pos, 0);
+	alsa_stream->period_offset = 0;
 	alsa_stream->draining = false;
 
 	return 0;
@@ -283,7 +278,7 @@ static int snd_bcm2835_pcm_trigger(struct snd_pcm_substream *substream, int cmd)
 		return bcm2835_audio_start(alsa_stream);
 	case SNDRV_PCM_TRIGGER_DRAIN:
 		alsa_stream->draining = true;
-		return 0;
+		return bcm2835_audio_drain(alsa_stream);
 	case SNDRV_PCM_TRIGGER_STOP:
 		return bcm2835_audio_stop(alsa_stream);
 	default:
@@ -300,7 +295,7 @@ snd_bcm2835_pcm_pointer(struct snd_pcm_substream *substream)
 
 	return snd_pcm_indirect_playback_pointer(substream,
 		&alsa_stream->pcm_indirect,
-		alsa_stream->pos);
+		atomic_read(&alsa_stream->pos));
 }
 
 /* operators */
@@ -338,6 +333,7 @@ int snd_bcm2835_new_pcm(struct bcm2835_chip *chip, u32 numchannels)
 	if (err < 0)
 		return err;
 	pcm->private_data = chip;
+	pcm->nonatomic = true;
 	strcpy(pcm->name, "bcm2835 ALSA");
 	chip->pcm = pcm;
 	chip->dest = AUDIO_DEST_AUTO;
@@ -367,6 +363,7 @@ int snd_bcm2835_new_spdif_pcm(struct bcm2835_chip *chip)
 		return err;
 
 	pcm->private_data = chip;
+	pcm->nonatomic = true;
 	strcpy(pcm->name, "bcm2835 IEC958/HDMI");
 	chip->pcm_spdif = pcm;
 	snd_pcm_set_ops(pcm, SNDRV_PCM_STREAM_PLAYBACK,
@@ -395,6 +392,7 @@ int snd_bcm2835_new_simple_pcm(struct bcm2835_chip *chip,
 		return err;
 
 	pcm->private_data = chip;
+	pcm->nonatomic = true;
 	strcpy(pcm->name, name);
 	chip->pcm = pcm;
 	chip->dest = route;

drivers/staging/vc04_services/bcm2835-audio/bcm2835-vchiq.c

@@ -26,10 +26,6 @@
 
 /* ---- Private Constants and Types ------------------------------------------ */
 
-#define BCM2835_AUDIO_STOP           0
-#define BCM2835_AUDIO_START          1
-#define BCM2835_AUDIO_WRITE          2
-
 /* Logging macros (for remapping to other logging mechanisms, i.e., printf) */
 #ifdef AUDIO_DEBUG_ENABLE
 #define LOG_ERR(fmt, arg...)   pr_err("%s:%d " fmt, __func__, __LINE__, ##arg)
@@ -55,17 +51,6 @@ struct bcm2835_audio_instance {
 
 static bool force_bulk;
 
-/* ---- Private Variables ---------------------------------------------------- */
-
-/* ---- Private Function Prototypes ------------------------------------------ */
-
-/* ---- Private Functions ---------------------------------------------------- */
-
-static int bcm2835_audio_stop_worker(struct bcm2835_alsa_stream *alsa_stream);
-static int bcm2835_audio_start_worker(struct bcm2835_alsa_stream *alsa_stream);
-static int bcm2835_audio_write_worker(struct bcm2835_alsa_stream *alsa_stream,
-				      unsigned int count, void *src);
-
 static void bcm2835_audio_lock(struct bcm2835_audio_instance *instance)
 {
 	mutex_lock(&instance->vchi_mutex);
@@ -135,108 +120,6 @@ static const u32 BCM2835_AUDIO_WRITE_COOKIE1 = ('B' << 24 | 'C' << 16 |
 static const u32 BCM2835_AUDIO_WRITE_COOKIE2 = ('D' << 24 | 'A' << 16 |
 						'T' << 8  | 'A');
 
-struct bcm2835_audio_work {
-	struct work_struct my_work;
-	struct bcm2835_alsa_stream *alsa_stream;
-	int cmd;
-	void *src;
-	unsigned int count;
-};
-
-static void my_wq_function(struct work_struct *work)
-{
-	struct bcm2835_audio_work *w =
-		container_of(work, struct bcm2835_audio_work, my_work);
-	int ret = -9;
-
-	switch (w->cmd) {
-	case BCM2835_AUDIO_START:
-		ret = bcm2835_audio_start_worker(w->alsa_stream);
-		break;
-	case BCM2835_AUDIO_STOP:
-		ret = bcm2835_audio_stop_worker(w->alsa_stream);
-		break;
-	case BCM2835_AUDIO_WRITE:
-		ret = bcm2835_audio_write_worker(w->alsa_stream, w->count,
-						 w->src);
-		break;
-	default:
-		LOG_ERR(" Unexpected work: %p:%d\n", w->alsa_stream, w->cmd);
-		break;
-	}
-	kfree((void *)work);
-}
-
-int bcm2835_audio_start(struct bcm2835_alsa_stream *alsa_stream)
-{
-	struct bcm2835_audio_work *work;
-
-	work = kmalloc(sizeof(*work), GFP_ATOMIC);
-	/*--- Queue some work (item 1) ---*/
-	if (!work) {
-		LOG_ERR(" .. Error: NULL work kmalloc\n");
-		return -ENOMEM;
-	}
-	INIT_WORK(&work->my_work, my_wq_function);
-	work->alsa_stream = alsa_stream;
-	work->cmd = BCM2835_AUDIO_START;
-	if (!queue_work(alsa_stream->my_wq, &work->my_work)) {
-		kfree(work);
-		return -EBUSY;
-	}
-	return 0;
-}
-
-int bcm2835_audio_stop(struct bcm2835_alsa_stream *alsa_stream)
-{
-	struct bcm2835_audio_work *work;
-
-	work = kmalloc(sizeof(*work), GFP_ATOMIC);
-	/*--- Queue some work (item 1) ---*/
-	if (!work) {
-		LOG_ERR(" .. Error: NULL work kmalloc\n");
-		return -ENOMEM;
-	}
-	INIT_WORK(&work->my_work, my_wq_function);
-	work->alsa_stream = alsa_stream;
-	work->cmd = BCM2835_AUDIO_STOP;
-	if (!queue_work(alsa_stream->my_wq, &work->my_work)) {
-		kfree(work);
-		return -EBUSY;
-	}
-	return 0;
-}
-
-int bcm2835_audio_write(struct bcm2835_alsa_stream *alsa_stream,
-			unsigned int count, void *src)
-{
-	struct bcm2835_audio_work *work;
-
-	work = kmalloc(sizeof(*work), GFP_ATOMIC);
-	/*--- Queue some work (item 1) ---*/
-	if (!work) {
-		LOG_ERR(" .. Error: NULL work kmalloc\n");
-		return -ENOMEM;
-	}
-	INIT_WORK(&work->my_work, my_wq_function);
-	work->alsa_stream = alsa_stream;
-	work->cmd = BCM2835_AUDIO_WRITE;
-	work->src = src;
-	work->count = count;
-	if (!queue_work(alsa_stream->my_wq, &work->my_work)) {
-		kfree(work);
-		return -EBUSY;
-	}
-	return 0;
-}
-
-static void my_workqueue_quit(struct bcm2835_alsa_stream *alsa_stream)
-{
-	flush_workqueue(alsa_stream->my_wq);
-	destroy_workqueue(alsa_stream->my_wq);
-	alsa_stream->my_wq = NULL;
-}
-
 static void audio_vchi_callback(void *param,
 				const VCHI_CALLBACK_REASON_T reason,
 				void *msg_handle)
@@ -249,47 +132,27 @@ static void audio_vchi_callback(void *param,
 	if (reason != VCHI_CALLBACK_MSG_AVAILABLE)
 		return;
 
-	if (!instance) {
-		LOG_ERR(" .. instance is null\n");
-		BUG();
-		return;
-	}
-	if (!instance->vchi_handle) {
-		LOG_ERR(" .. instance->vchi_handle is null\n");
-		BUG();
-		return;
-	}
 	status = vchi_msg_dequeue(instance->vchi_handle,
 				  &m, sizeof(m), &msg_len, VCHI_FLAGS_NONE);
 	if (m.type == VC_AUDIO_MSG_TYPE_RESULT) {
-		LOG_DBG(" .. instance=%p, m.type=VC_AUDIO_MSG_TYPE_RESULT, success=%d\n",
-			instance, m.u.result.success);
 		instance->result = m.u.result.success;
 		complete(&instance->msg_avail_comp);
 	} else if (m.type == VC_AUDIO_MSG_TYPE_COMPLETE) {
-		struct bcm2835_alsa_stream *alsa_stream = instance->alsa_stream;
-
-		LOG_DBG(" .. instance=%p, m.type=VC_AUDIO_MSG_TYPE_COMPLETE, complete=%d\n",
-			instance, m.u.complete.count);
 		if (m.u.complete.cookie1 != BCM2835_AUDIO_WRITE_COOKIE1 ||
 		    m.u.complete.cookie2 != BCM2835_AUDIO_WRITE_COOKIE2)
-			LOG_ERR(" .. response is corrupt\n");
-		else if (alsa_stream) {
-			atomic_add(m.u.complete.count,
-				   &alsa_stream->retrieved);
-			bcm2835_playback_fifo(alsa_stream);
-		} else {
-			LOG_ERR(" .. unexpected alsa_stream=%p\n",
-				alsa_stream);
-		}
+			LOG_ERR("invalid cookie\n");
+		else
+			bcm2835_playback_fifo(instance->alsa_stream,
+					      m.u.complete.count);
 	} else {
-		LOG_ERR(" .. unexpected m.type=%d\n", m.type);
+		LOG_ERR("unexpected callback type=%d\n", m.type);
 	}
 }
 
-static struct bcm2835_audio_instance *
+static int
 vc_vchi_audio_init(VCHI_INSTANCE_T vchi_instance,
-		   VCHI_CONNECTION_T *vchi_connection)
+		   VCHI_CONNECTION_T *vchi_connection,
+		   struct bcm2835_audio_instance *instance)
 {
 	SERVICE_CREATION_T params = {
 		.version		= VCHI_VERSION_EX(VC_AUDIOSERV_VER, VC_AUDIOSERV_MIN_VER),
@@ -298,23 +161,14 @@ vc_vchi_audio_init(VCHI_INSTANCE_T vchi_instance,
 		.rx_fifo_size		= 0,
 		.tx_fifo_size		= 0,
 		.callback		= audio_vchi_callback,
+		.callback_param		= instance,
 		.want_unaligned_bulk_rx = 1, //TODO: remove VCOS_FALSE
 		.want_unaligned_bulk_tx = 1, //TODO: remove VCOS_FALSE
 		.want_crc		= 0
 	};
-	struct bcm2835_audio_instance *instance;
 	int status;
 
-	/* Allocate memory for this instance */
-	instance = kzalloc(sizeof(*instance), GFP_KERNEL);
-	if (!instance)
-		return ERR_PTR(-ENOMEM);
-
-	/* Create a lock for exclusive, serialized VCHI connection access */
-	mutex_init(&instance->vchi_mutex);
 	/* Open the VCHI service connections */
-	params.callback_param = instance,
-
 	status = vchi_service_open(vchi_instance, &params,
 				   &instance->vchi_handle);
 
@@ -322,16 +176,16 @@ vc_vchi_audio_init(VCHI_INSTANCE_T vchi_instance,
 		LOG_ERR("%s: failed to open VCHI service connection (status=%d)\n",
 			__func__, status);
 		kfree(instance);
-		return ERR_PTR(-EPERM);
+		return -EPERM;
 	}
 
 	/* Finished with the service for now */
 	vchi_service_release(instance->vchi_handle);
 
-	return instance;
+	return 0;
 }
 
-static int vc_vchi_audio_deinit(struct bcm2835_audio_instance *instance)
+static void vc_vchi_audio_deinit(struct bcm2835_audio_instance *instance)
 {
 	int status;
 
@@ -346,10 +200,6 @@ static int vc_vchi_audio_deinit(struct bcm2835_audio_instance *instance)
 	}
 
 	mutex_unlock(&instance->vchi_mutex);
-
-	kfree(instance);
-
-	return 0;
 }
 
 int bcm2835_new_vchi_ctx(struct bcm2835_vchi_ctx *vchi_ctx)
@@ -387,39 +237,25 @@ void bcm2835_free_vchi_ctx(struct bcm2835_vchi_ctx *vchi_ctx)
 	vchi_ctx->vchi_instance = NULL;
 }
 
-static int bcm2835_audio_open_connection(struct bcm2835_alsa_stream *alsa_stream)
-{
-	struct bcm2835_audio_instance *instance =
-		(struct bcm2835_audio_instance *)alsa_stream->instance;
-	struct bcm2835_vchi_ctx *vhci_ctx = alsa_stream->chip->vchi_ctx;
-
-	/* Initialize an instance of the audio service */
-	instance = vc_vchi_audio_init(vhci_ctx->vchi_instance,
-				      vhci_ctx->vchi_connection);
-
-	if (IS_ERR(instance))
-		return PTR_ERR(instance);
-
-	instance->alsa_stream = alsa_stream;
-	alsa_stream->instance = instance;
-
-	return 0;
-}
-
 int bcm2835_audio_open(struct bcm2835_alsa_stream *alsa_stream)
 {
+	struct bcm2835_vchi_ctx *vchi_ctx = alsa_stream->chip->vchi_ctx;
 	struct bcm2835_audio_instance *instance;
 	int err;
 
-	alsa_stream->my_wq = alloc_workqueue("my_queue", WQ_HIGHPRI, 1);
-	if (!alsa_stream->my_wq)
+	/* Allocate memory for this instance */
+	instance = kzalloc(sizeof(*instance), GFP_KERNEL);
+	if (!instance)
 		return -ENOMEM;
+	mutex_init(&instance->vchi_mutex);
+	instance->alsa_stream = alsa_stream;
+	alsa_stream->instance = instance;
 
-	err = bcm2835_audio_open_connection(alsa_stream);
+	err = vc_vchi_audio_init(vchi_ctx->vchi_instance,
+				 vchi_ctx->vchi_connection,
+				 instance);
 	if (err < 0)
-		goto free_wq;
-
-	instance = alsa_stream->instance;
+		goto free_instance;
 
 	err = bcm2835_audio_send_simple(instance, VC_AUDIO_MSG_TYPE_OPEN,
 					false);
@@ -438,8 +274,9 @@ int bcm2835_audio_open(struct bcm2835_alsa_stream *alsa_stream)
 
  deinit:
 	vc_vchi_audio_deinit(instance);
- free_wq:
-	destroy_workqueue(alsa_stream->my_wq);
+ free_instance:
+	alsa_stream->instance = NULL;
+	kfree(instance);
 	return err;
 }
 
@@ -478,37 +315,46 @@ int bcm2835_audio_set_params(struct bcm2835_alsa_stream *alsa_stream,
 	return bcm2835_audio_send_msg(alsa_stream->instance, &m, true);
 }
 
-static int bcm2835_audio_start_worker(struct bcm2835_alsa_stream *alsa_stream)
+int bcm2835_audio_start(struct bcm2835_alsa_stream *alsa_stream)
 {
 	return bcm2835_audio_send_simple(alsa_stream->instance,
 					 VC_AUDIO_MSG_TYPE_START, false);
 }
 
-static int bcm2835_audio_stop_worker(struct bcm2835_alsa_stream *alsa_stream)
+int bcm2835_audio_stop(struct bcm2835_alsa_stream *alsa_stream)
 {
 	return bcm2835_audio_send_simple(alsa_stream->instance,
 					 VC_AUDIO_MSG_TYPE_STOP, false);
 }
 
+int bcm2835_audio_drain(struct bcm2835_alsa_stream *alsa_stream)
+{
+	struct vc_audio_msg m = {
+		.type = VC_AUDIO_MSG_TYPE_STOP,
+		.u.stop.draining = 1,
+	};
+
+	return bcm2835_audio_send_msg(alsa_stream->instance, &m, false);
+}
+
 int bcm2835_audio_close(struct bcm2835_alsa_stream *alsa_stream)
 {
 	struct bcm2835_audio_instance *instance = alsa_stream->instance;
 	int err;
 
-	my_workqueue_quit(alsa_stream);
-
 	err = bcm2835_audio_send_simple(alsa_stream->instance,
 					VC_AUDIO_MSG_TYPE_CLOSE, true);
 
 	/* Stop the audio service */
 	vc_vchi_audio_deinit(instance);
 	alsa_stream->instance = NULL;
+	kfree(instance);
 
 	return err;
 }
 
-static int bcm2835_audio_write_worker(struct bcm2835_alsa_stream *alsa_stream,
-				      unsigned int size, void *src)
+int bcm2835_audio_write(struct bcm2835_alsa_stream *alsa_stream,
+			unsigned int size, void *src)
 {
 	struct bcm2835_audio_instance *instance = alsa_stream->instance;
 	struct vc_audio_msg m = {
@@ -558,13 +404,5 @@ static int bcm2835_audio_write_worker(struct bcm2835_alsa_stream *alsa_stream,
 	return err;
 }
 
-unsigned int bcm2835_audio_retrieve_buffers(struct bcm2835_alsa_stream *alsa_stream)
-{
-	unsigned int count = atomic_read(&alsa_stream->retrieved);
-
-	atomic_sub(count, &alsa_stream->retrieved);
-	return count;
-}
-
 module_param(force_bulk, bool, 0444);
 MODULE_PARM_DESC(force_bulk, "Force use of vchiq bulk for audio");

drivers/staging/vc04_services/bcm2835-audio/bcm2835.h

@@ -121,13 +121,12 @@ struct bcm2835_alsa_stream {
 
 	int draining;
 
-	unsigned int pos;
+	atomic_t pos;
+	unsigned int period_offset;
 	unsigned int buffer_size;
 	unsigned int period_size;
 
-	atomic_t retrieved;
 	struct bcm2835_audio_instance *instance;
-	struct workqueue_struct *my_wq;
 	int idx;
 };
 
@@ -152,11 +151,13 @@ int bcm2835_audio_set_params(struct bcm2835_alsa_stream *alsa_stream,
 			     unsigned int bps);
 int bcm2835_audio_start(struct bcm2835_alsa_stream *alsa_stream);
 int bcm2835_audio_stop(struct bcm2835_alsa_stream *alsa_stream);
+int bcm2835_audio_drain(struct bcm2835_alsa_stream *alsa_stream);
 int bcm2835_audio_set_ctls(struct bcm2835_alsa_stream *alsa_stream);
 int bcm2835_audio_write(struct bcm2835_alsa_stream *alsa_stream,
 			unsigned int count,
 			void *src);
-void bcm2835_playback_fifo(struct bcm2835_alsa_stream *alsa_stream);
+void bcm2835_playback_fifo(struct bcm2835_alsa_stream *alsa_stream,
+			   unsigned int size);
 unsigned int bcm2835_audio_retrieve_buffers(struct bcm2835_alsa_stream *alsa_stream);
 
 #endif /* __SOUND_ARM_BCM2835_H */