recipes-kernel: add MOST driver kernel modules

This commit adds the recipes-kernel directory to the meta-agl-demo
layer. It is needed to add the MOST driver to the AGL layer and have
it compiled as out-of-tree modules.

Change-Id: I38174a2f9a59b0424cfaf2f85f059550422f58f2
Signed-off-by: Christian Gromm <christian.gromm@microchip.com>

4 files changed, 1147 insertions, 0 deletions

diff --git a/recipes-kernel/aim-sound/aim-sound.bb b/recipes-kernel/aim-sound/aim-sound.bb
new file mode 100644
index 000000000..565b1a563
--- /dev/null
+++ b/recipes-kernel/aim-sound/aim-sound.bb
@@ -0,0 +1,21 @@
+DESCRIPTION = "Example of how to build an external Linux kernel module"
+LICENSE = "GPLv2"
+LIC_FILES_CHKSUM = "file://COPYING;md5=12f884d2ae1ff87c09e5b7ccc2c4ca7e \
+		    file://sound.c;md5=5306a2a73f0855ecf71a8241796517a6 \ 
+		   "
+
+inherit module
+
+PR = "r0"
+PV = "0.1"
+
+SRC_URI = "file://Makefile \
+	   file://../../mostcore/files/mostcore.h \
+	   file://sound.c \
+	   file://COPYING \
+	  "
+
+S = "${WORKDIR}"
+
+# The inherit of module.bbclass will automatically name module packages with
+# "kernel-module-" prefix as required by the oe-core build environment.
diff --git a/recipes-kernel/aim-sound/files/COPYING b/recipes-kernel/aim-sound/files/COPYING
new file mode 100644
index 000000000..6d45519c8
--- /dev/null
+++ b/recipes-kernel/aim-sound/files/COPYING
@@ -0,0 +1,340 @@
+		    GNU GENERAL PUBLIC LICENSE
+		       Version 2, June 1991
+
+ Copyright (C) 1989, 1991 Free Software Foundation, Inc.
+                       51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
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diff --git a/recipes-kernel/aim-sound/files/Makefile b/recipes-kernel/aim-sound/files/Makefile
new file mode 100644
index 000000000..9defcc5e2
--- /dev/null
+++ b/recipes-kernel/aim-sound/files/Makefile
@@ -0,0 +1,18 @@
+# Makefile
+#
+
+SRC := $(shell pwd)
+
+obj-m += aim_sound.o
+aim_sound-y := sound.o
+CFLAGS_sound.o := -I$(src)/../../mostcore/files/
+
+all:
+	$(MAKE) -C $(KERNEL_SRC) M=$(SRC) modules
+
+modules_install:
+	$(MAKE) -C $(KERNEL_SRC) M=$(SRC) modules_install
+
+clean:
+	$(MAKE) -C $(KERNEL_SRC) M=$(SRC) clean
+
diff --git a/recipes-kernel/aim-sound/files/sound.c b/recipes-kernel/aim-sound/files/sound.c
new file mode 100644
index 000000000..63b866b3c
--- /dev/null
+++ b/recipes-kernel/aim-sound/files/sound.c
@@ -0,0 +1,768 @@
+/*
+ * sound.c - Audio Application Interface Module for Mostcore
+ *
+ * Copyright (C) 2015 Microchip Technology Germany II GmbH & Co. KG
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * This file is licensed under GPLv2.
+ */
+
+#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
+
+#include <linux/module.h>
+#include <linux/printk.h>
+#include <linux/kernel.h>
+#include <linux/init.h>
+#include <sound/core.h>
+#include <sound/pcm.h>
+#include <sound/pcm_params.h>
+#include <linux/sched.h>
+#include <linux/kthread.h>
+#include <mostcore.h>
+
+#define DRIVER_NAME "sound"
+
+static struct list_head dev_list;
+static struct most_aim audio_aim;
+
+/**
+ * struct channel - private structure to keep channel specific data
+ * @substream: stores the substream structure
+ * @iface: interface for which the channel belongs to
+ * @cfg: channel configuration
+ * @card: registered sound card
+ * @list: list for private use
+ * @id: channel index
+ * @period_pos: current period position (ring buffer)
+ * @buffer_pos: current buffer position (ring buffer)
+ * @is_stream_running: identifies whether a stream is running or not
+ * @opened: set when the stream is opened
+ * @playback_task: playback thread
+ * @playback_waitq: waitq used by playback thread
+ */
+struct channel {
+	struct snd_pcm_substream *substream;
+	struct snd_pcm_hardware pcm_hardware;
+	struct most_interface *iface;
+	struct most_channel_config *cfg;
+	struct snd_card *card;
+	struct list_head list;
+	int id;
+	unsigned int period_pos;
+	unsigned int buffer_pos;
+	bool is_stream_running;
+
+	struct task_struct *playback_task;
+	wait_queue_head_t playback_waitq;
+
+	void (*copy_fn)(void *alsa, void *most, unsigned int bytes);
+};
+
+#define MOST_PCM_INFO (SNDRV_PCM_INFO_MMAP | \
+		       SNDRV_PCM_INFO_MMAP_VALID | \
+		       SNDRV_PCM_INFO_BATCH | \
+		       SNDRV_PCM_INFO_INTERLEAVED | \
+		       SNDRV_PCM_INFO_BLOCK_TRANSFER)
+
+#define swap16(val) ( \
+	(((u16)(val) << 8) & (u16)0xFF00) | \
+	(((u16)(val) >> 8) & (u16)0x00FF))
+
+#define swap32(val) ( \
+	(((u32)(val) << 24) & (u32)0xFF000000) | \
+	(((u32)(val) <<  8) & (u32)0x00FF0000) | \
+	(((u32)(val) >>  8) & (u32)0x0000FF00) | \
+	(((u32)(val) >> 24) & (u32)0x000000FF))
+
+static void swap_copy16(u16 *dest, const u16 *source, unsigned int bytes)
+{
+	unsigned int i = 0;
+
+	while (i < (bytes / 2)) {
+		dest[i] = swap16(source[i]);
+		i++;
+	}
+}
+
+static void swap_copy24(u8 *dest, const u8 *source, unsigned int bytes)
+{
+	unsigned int i = 0;
+
+	while (i < bytes - 2) {
+		dest[i] = source[i + 2];
+		dest[i + 1] = source[i + 1];
+		dest[i + 2] = source[i];
+		i += 3;
+	}
+}
+
+static void swap_copy32(u32 *dest, const u32 *source, unsigned int bytes)
+{
+	unsigned int i = 0;
+
+	while (i < bytes / 4) {
+		dest[i] = swap32(source[i]);
+		i++;
+	}
+}
+
+static void alsa_to_most_memcpy(void *alsa, void *most, unsigned int bytes)
+{
+	memcpy(most, alsa, bytes);
+}
+
+static void alsa_to_most_copy16(void *alsa, void *most, unsigned int bytes)
+{
+	swap_copy16(most, alsa, bytes);
+}
+
+static void alsa_to_most_copy24(void *alsa, void *most, unsigned int bytes)
+{
+	swap_copy24(most, alsa, bytes);
+}
+
+static void alsa_to_most_copy32(void *alsa, void *most, unsigned int bytes)
+{
+	swap_copy32(most, alsa, bytes);
+}
+
+static void most_to_alsa_memcpy(void *alsa, void *most, unsigned int bytes)
+{
+	memcpy(alsa, most, bytes);
+}
+
+static void most_to_alsa_copy16(void *alsa, void *most, unsigned int bytes)
+{
+	swap_copy16(alsa, most, bytes);
+}
+
+static void most_to_alsa_copy24(void *alsa, void *most, unsigned int bytes)
+{
+	swap_copy24(alsa, most, bytes);
+}
+
+static void most_to_alsa_copy32(void *alsa, void *most, unsigned int bytes)
+{
+	swap_copy32(alsa, most, bytes);
+}
+
+/**
+ * get_channel - get pointer to channel
+ * @iface: interface structure
+ * @channel_id: channel ID
+ *
+ * This traverses the channel list and returns the channel matching the
+ * ID and interface.
+ *
+ * Returns pointer to channel on success or NULL otherwise.
+ */
+static struct channel *get_channel(struct most_interface *iface,
+				   int channel_id)
+{
+	struct channel *channel, *tmp;
+
+	list_for_each_entry_safe(channel, tmp, &dev_list, list) {
+		if ((channel->iface == iface) && (channel->id == channel_id))
+			return channel;
+	}
+
+	return NULL;
+}
+
+/**
+ * copy_data - implements data copying function
+ * @channel: channel
+ * @mbo: MBO from core
+ *
+ * Copy data from/to ring buffer to/from MBO and update the buffer position
+ */
+static bool copy_data(struct channel *channel, struct mbo *mbo)
+{
+	struct snd_pcm_runtime *const runtime = channel->substream->runtime;
+	unsigned int const frame_bytes = channel->cfg->subbuffer_size;
+	unsigned int const buffer_size = runtime->buffer_size;
+	unsigned int frames;
+	unsigned int fr0;
+
+	if (channel->cfg->direction & MOST_CH_RX)
+		frames = mbo->processed_length / frame_bytes;
+	else
+		frames = mbo->buffer_length / frame_bytes;
+	fr0 = min(buffer_size - channel->buffer_pos, frames);
+
+	channel->copy_fn(runtime->dma_area + channel->buffer_pos * frame_bytes,
+			 mbo->virt_address,
+			 fr0 * frame_bytes);
+
+	if (frames > fr0) {
+		/* wrap around at end of ring buffer */
+		channel->copy_fn(runtime->dma_area,
+				 mbo->virt_address + fr0 * frame_bytes,
+				 (frames - fr0) * frame_bytes);
+	}
+
+	channel->buffer_pos += frames;
+	if (channel->buffer_pos >= buffer_size)
+		channel->buffer_pos -= buffer_size;
+	channel->period_pos += frames;
+	if (channel->period_pos >= runtime->period_size) {
+		channel->period_pos -= runtime->period_size;
+		return true;
+	}
+
+	return false;
+}
+
+/**
+ * playback_thread - function implements the playback thread
+ * @data: private data
+ *
+ * Thread which does the playback functionality in a loop. It waits for a free
+ * MBO from mostcore for a particular channel and copy the data from ring buffer
+ * to MBO. Submit the MBO back to mostcore, after copying the data.
+ *
+ * Returns 0 on success or error code otherwise.
+ */
+static int playback_thread(void *data)
+{
+	struct channel *const channel = data;
+
+	while (!kthread_should_stop()) {
+		struct mbo *mbo = NULL;
+		bool period_elapsed = false;
+		int ret;
+
+		wait_event_interruptible(
+			channel->playback_waitq,
+			kthread_should_stop() ||
+			(channel->is_stream_running &&
+			 (mbo = most_get_mbo(channel->iface, channel->id,
+					     &audio_aim))));
+		if (!mbo)
+			continue;
+
+		if (channel->is_stream_running)
+			period_elapsed = copy_data(channel, mbo);
+		else
+			memset(mbo->virt_address, 0, mbo->buffer_length);
+
+		ret = most_submit_mbo(mbo);
+		if (ret)
+			channel->is_stream_running = false;
+
+		if (period_elapsed)
+			snd_pcm_period_elapsed(channel->substream);
+	}
+
+	return 0;
+}
+
+/**
+ * pcm_open - implements open callback function for PCM middle layer
+ * @substream: pointer to ALSA PCM substream
+ *
+ * This is called when a PCM substream is opened. At least, the function should
+ * initialize the runtime->hw record.
+ *
+ * Returns 0 on success or error code otherwise.
+ */
+static int pcm_open(struct snd_pcm_substream *substream)
+{
+	struct channel *channel = substream->private_data;
+	struct snd_pcm_runtime *runtime = substream->runtime;
+	struct most_channel_config *cfg = channel->cfg;
+
+	channel->substream = substream;
+
+	if (cfg->direction == MOST_CH_TX) {
+		channel->playback_task = kthread_run(playback_thread, channel,
+						     "most_audio_playback");
+		if (IS_ERR(channel->playback_task)) {
+			pr_err("Couldn't start thread\n");
+			return PTR_ERR(channel->playback_task);
+		}
+	}
+
+	if (most_start_channel(channel->iface, channel->id, &audio_aim)) {
+		pr_err("most_start_channel() failed!\n");
+		if (cfg->direction == MOST_CH_TX)
+			kthread_stop(channel->playback_task);
+		return -EBUSY;
+	}
+
+	runtime->hw = channel->pcm_hardware;
+	return 0;
+}
+
+/**
+ * pcm_close - implements close callback function for PCM middle layer
+ * @substream: sub-stream pointer
+ *
+ * Obviously, this is called when a PCM substream is closed. Any private
+ * instance for a PCM substream allocated in the open callback will be
+ * released here.
+ *
+ * Returns 0 on success or error code otherwise.
+ */
+static int pcm_close(struct snd_pcm_substream *substream)
+{
+	struct channel *channel = substream->private_data;
+
+	if (channel->cfg->direction == MOST_CH_TX)
+		kthread_stop(channel->playback_task);
+	most_stop_channel(channel->iface, channel->id, &audio_aim);
+
+	return 0;
+}
+
+/**
+ * pcm_hw_params - implements hw_params callback function for PCM middle layer
+ * @substream: sub-stream pointer
+ * @hw_params: contains the hardware parameters set by the application
+ *
+ * This is called when the hardware parameters is set by the application, that
+ * is, once when the buffer size, the period size, the format, etc. are defined
+ * for the PCM substream. Many hardware setups should be done is this callback,
+ * including the allocation of buffers.
+ *
+ * Returns 0 on success or error code otherwise.
+ */
+static int pcm_hw_params(struct snd_pcm_substream *substream,
+			 struct snd_pcm_hw_params *hw_params)
+{
+	struct channel *channel = substream->private_data;
+
+	if ((params_channels(hw_params) > channel->pcm_hardware.channels_max) ||
+	    (params_channels(hw_params) < channel->pcm_hardware.channels_min)) {
+		pr_err("Requested number of channels not supported.\n");
+		return -EINVAL;
+	}
+	return snd_pcm_lib_alloc_vmalloc_buffer(substream,
+						params_buffer_bytes(hw_params));
+}
+
+/**
+ * pcm_hw_free - implements hw_free callback function for PCM middle layer
+ * @substream: substream pointer
+ *
+ * This is called to release the resources allocated via hw_params.
+ * This function will be always called before the close callback is called.
+ *
+ * Returns 0 on success or error code otherwise.
+ */
+static int pcm_hw_free(struct snd_pcm_substream *substream)
+{
+	return snd_pcm_lib_free_vmalloc_buffer(substream);
+}
+
+/**
+ * pcm_prepare - implements prepare callback function for PCM middle layer
+ * @substream: substream pointer
+ *
+ * This callback is called when the PCM is "prepared". Format rate, sample rate,
+ * etc., can be set here. This callback can be called many times at each setup.
+ *
+ * Returns 0 on success or error code otherwise.
+ */
+static int pcm_prepare(struct snd_pcm_substream *substream)
+{
+	struct channel *channel = substream->private_data;
+	struct snd_pcm_runtime *runtime = substream->runtime;
+	struct most_channel_config *cfg = channel->cfg;
+	int width = snd_pcm_format_physical_width(runtime->format);
+
+	channel->copy_fn = NULL;
+
+	if (cfg->direction == MOST_CH_TX) {
+		if (snd_pcm_format_big_endian(runtime->format) || width == 8)
+			channel->copy_fn = alsa_to_most_memcpy;
+		else if (width == 16)
+			channel->copy_fn = alsa_to_most_copy16;
+		else if (width == 24)
+			channel->copy_fn = alsa_to_most_copy24;
+		else if (width == 32)
+			channel->copy_fn = alsa_to_most_copy32;
+	} else {
+		if (snd_pcm_format_big_endian(runtime->format) || width == 8)
+			channel->copy_fn = most_to_alsa_memcpy;
+		else if (width == 16)
+			channel->copy_fn = most_to_alsa_copy16;
+		else if (width == 24)
+			channel->copy_fn = most_to_alsa_copy24;
+		else if (width == 32)
+			channel->copy_fn = most_to_alsa_copy32;
+	}
+
+	if (!channel->copy_fn) {
+		pr_err("unsupported format\n");
+		return -EINVAL;
+	}
+
+	channel->period_pos = 0;
+	channel->buffer_pos = 0;
+
+	return 0;
+}
+
+/**
+ * pcm_trigger - implements trigger callback function for PCM middle layer
+ * @substream: substream pointer
+ * @cmd: action to perform
+ *
+ * This is called when the PCM is started, stopped or paused. The action will be
+ * specified in the second argument, SNDRV_PCM_TRIGGER_XXX
+ *
+ * Returns 0 on success or error code otherwise.
+ */
+static int pcm_trigger(struct snd_pcm_substream *substream, int cmd)
+{
+	struct channel *channel = substream->private_data;
+
+	switch (cmd) {
+	case SNDRV_PCM_TRIGGER_START:
+		channel->is_stream_running = true;
+		wake_up_interruptible(&channel->playback_waitq);
+		return 0;
+
+	case SNDRV_PCM_TRIGGER_STOP:
+		channel->is_stream_running = false;
+		return 0;
+
+	default:
+		pr_info("pcm_trigger(), invalid\n");
+		return -EINVAL;
+	}
+	return 0;
+}
+
+/**
+ * pcm_pointer - implements pointer callback function for PCM middle layer
+ * @substream: substream pointer
+ *
+ * This callback is called when the PCM middle layer inquires the current
+ * hardware position on the buffer. The position must be returned in frames,
+ * ranging from 0 to buffer_size-1.
+ */
+static snd_pcm_uframes_t pcm_pointer(struct snd_pcm_substream *substream)
+{
+	struct channel *channel = substream->private_data;
+
+	return channel->buffer_pos;
+}
+
+/**
+ * Initialization of struct snd_pcm_ops
+ */
+static struct snd_pcm_ops pcm_ops = {
+	.open       = pcm_open,
+	.close      = pcm_close,
+	.ioctl      = snd_pcm_lib_ioctl,
+	.hw_params  = pcm_hw_params,
+	.hw_free    = pcm_hw_free,
+	.prepare    = pcm_prepare,
+	.trigger    = pcm_trigger,
+	.pointer    = pcm_pointer,
+	.page       = snd_pcm_lib_get_vmalloc_page,
+	.mmap       = snd_pcm_lib_mmap_vmalloc,
+};
+
+static int split_arg_list(char *buf, char **card_name, char **pcm_format)
+{
+	*card_name = strsep(&buf, ".");
+	if (!*card_name)
+		return -EIO;
+	*pcm_format = strsep(&buf, ".\n");
+	if (!*pcm_format)
+		return -EIO;
+	return 0;
+}
+
+static int audio_set_hw_params(struct snd_pcm_hardware *pcm_hw,
+			       char *pcm_format,
+			       struct most_channel_config *cfg)
+{
+	pcm_hw->info = MOST_PCM_INFO;
+	pcm_hw->rates = SNDRV_PCM_RATE_48000;
+	pcm_hw->rate_min = 48000;
+	pcm_hw->rate_max = 48000;
+	pcm_hw->buffer_bytes_max = cfg->num_buffers * cfg->buffer_size;
+	pcm_hw->period_bytes_min = cfg->buffer_size;
+	pcm_hw->period_bytes_max = cfg->buffer_size;
+	pcm_hw->periods_min = 1;
+	pcm_hw->periods_max = cfg->num_buffers;
+
+	if (!strcmp(pcm_format, "1x8")) {
+		if (cfg->subbuffer_size != 1)
+			goto error;
+		pr_info("PCM format is 8-bit mono\n");
+		pcm_hw->channels_min = 1;
+		pcm_hw->channels_max = 1;
+		pcm_hw->formats = SNDRV_PCM_FMTBIT_S8;
+	} else if (!strcmp(pcm_format, "2x16")) {
+		if (cfg->subbuffer_size != 4)
+			goto error;
+		pr_info("PCM format is 16-bit stereo\n");
+		pcm_hw->channels_min = 2;
+		pcm_hw->channels_max = 2;
+		pcm_hw->formats = SNDRV_PCM_FMTBIT_S16_LE |
+				  SNDRV_PCM_FMTBIT_S16_BE;
+	} else if (!strcmp(pcm_format, "2x24")) {
+		if (cfg->subbuffer_size != 6)
+			goto error;
+		pr_info("PCM format is 24-bit stereo\n");
+		pcm_hw->channels_min = 2;
+		pcm_hw->channels_max = 2;
+		pcm_hw->formats = SNDRV_PCM_FMTBIT_S24_3LE |
+				  SNDRV_PCM_FMTBIT_S24_3BE;
+	} else if (!strcmp(pcm_format, "2x32")) {
+		if (cfg->subbuffer_size != 8)
+			goto error;
+		pr_info("PCM format is 32-bit stereo\n");
+		pcm_hw->channels_min = 2;
+		pcm_hw->channels_max = 2;
+		pcm_hw->formats = SNDRV_PCM_FMTBIT_S32_LE |
+				  SNDRV_PCM_FMTBIT_S32_BE;
+	} else if (!strcmp(pcm_format, "6x16")) {
+		if (cfg->subbuffer_size != 12)
+			goto error;
+		pr_info("PCM format is 16-bit 5.1 multi channel\n");
+		pcm_hw->channels_min = 6;
+		pcm_hw->channels_max = 6;
+		pcm_hw->formats = SNDRV_PCM_FMTBIT_S16_LE |
+				  SNDRV_PCM_FMTBIT_S16_BE;
+	} else {
+		pr_err("PCM format %s not supported\n", pcm_format);
+		return -EIO;
+	}
+	return 0;
+error:
+	pr_err("Audio resolution doesn't fit subbuffer size\n");
+	return -EINVAL;
+}
+
+/**
+ * audio_probe_channel - probe function of the driver module
+ * @iface: pointer to interface instance
+ * @channel_id: channel index/ID
+ * @cfg: pointer to actual channel configuration
+ * @parent: pointer to kobject (needed for sysfs hook-up)
+ * @arg_list: string that provides the name of the device to be created in /dev
+ *	      plus the desired audio resolution
+ *
+ * Creates sound card, pcm device, sets pcm ops and registers sound card.
+ *
+ * Returns 0 on success or error code otherwise.
+ */
+static int audio_probe_channel(struct most_interface *iface, int channel_id,
+			       struct most_channel_config *cfg,
+			       struct kobject *parent, char *arg_list)
+{
+	struct channel *channel;
+	struct snd_card *card;
+	struct snd_pcm *pcm;
+	int playback_count = 0;
+	int capture_count = 0;
+	int ret;
+	int direction;
+	char *card_name;
+	char *pcm_format;
+
+	if (!iface)
+		return -EINVAL;
+
+	if (cfg->data_type != MOST_CH_SYNC) {
+		pr_err("Incompatible channel type\n");
+		return -EINVAL;
+	}
+
+	if (get_channel(iface, channel_id)) {
+		pr_err("channel (%s:%d) is already linked\n",
+		       iface->description, channel_id);
+		return -EINVAL;
+	}
+
+	if (cfg->direction == MOST_CH_TX) {
+		playback_count = 1;
+		direction = SNDRV_PCM_STREAM_PLAYBACK;
+	} else {
+		capture_count = 1;
+		direction = SNDRV_PCM_STREAM_CAPTURE;
+	}
+
+	ret = split_arg_list(arg_list, &card_name, &pcm_format);
+	if (ret < 0) {
+		pr_info("PCM format missing\n");
+		return ret;
+	}
+
+	ret = snd_card_create(-1, card_name, THIS_MODULE,
+-			      sizeof(*channel), &card);
+	if (ret < 0)
+		return ret;
+
+	channel = card->private_data;
+	channel->card = card;
+	channel->cfg = cfg;
+	channel->iface = iface;
+	channel->id = channel_id;
+	init_waitqueue_head(&channel->playback_waitq);
+
+	if (audio_set_hw_params(&channel->pcm_hardware, pcm_format, cfg))
+		goto err_free_card;
+
+	snprintf(card->driver, sizeof(card->driver), "%s", DRIVER_NAME);
+	snprintf(card->shortname, sizeof(card->shortname), "Microchip MOST:%d",
+		 card->number);
+	snprintf(card->longname, sizeof(card->longname), "%s at %s, ch %d",
+		 card->shortname, iface->description, channel_id);
+
+	ret = snd_pcm_new(card, card_name, 0, playback_count,
+			  capture_count, &pcm);
+	if (ret < 0)
+		goto err_free_card;
+
+	pcm->private_data = channel;
+
+	snd_pcm_set_ops(pcm, direction, &pcm_ops);
+
+	ret = snd_card_register(card);
+	if (ret < 0)
+		goto err_free_card;
+
+	list_add_tail(&channel->list, &dev_list);
+
+	return 0;
+
+err_free_card:
+	snd_card_free(card);
+	return ret;
+}
+
+/**
+ * audio_disconnect_channel - function to disconnect a channel
+ * @iface: pointer to interface instance
+ * @channel_id: channel index
+ *
+ * This frees allocated memory and removes the sound card from ALSA
+ *
+ * Returns 0 on success or error code otherwise.
+ */
+static int audio_disconnect_channel(struct most_interface *iface,
+				    int channel_id)
+{
+	struct channel *channel;
+
+	channel = get_channel(iface, channel_id);
+	if (!channel) {
+		pr_err("sound_disconnect_channel(), invalid channel %d\n",
+		       channel_id);
+		return -EINVAL;
+	}
+
+	list_del(&channel->list);
+	snd_card_free(channel->card);
+
+	return 0;
+}
+
+/**
+ * audio_rx_completion - completion handler for rx channels
+ * @mbo: pointer to buffer object that has completed
+ *
+ * This searches for the channel this MBO belongs to and copy the data from MBO
+ * to ring buffer
+ *
+ * Returns 0 on success or error code otherwise.
+ */
+static int audio_rx_completion(struct mbo *mbo)
+{
+	struct channel *channel = get_channel(mbo->ifp, mbo->hdm_channel_id);
+	bool period_elapsed = false;
+
+	if (!channel) {
+		pr_err("sound_rx_completion(), invalid channel %d\n",
+		       mbo->hdm_channel_id);
+		return -EINVAL;
+	}
+
+	if (channel->is_stream_running)
+		period_elapsed = copy_data(channel, mbo);
+
+	most_put_mbo(mbo);
+
+	if (period_elapsed)
+		snd_pcm_period_elapsed(channel->substream);
+
+	return 0;
+}
+
+/**
+ * audio_tx_completion - completion handler for tx channels
+ * @iface: pointer to interface instance
+ * @channel_id: channel index/ID
+ *
+ * This searches the channel that belongs to this combination of interface
+ * pointer and channel ID and wakes a process sitting in the wait queue of
+ * this channel.
+ *
+ * Returns 0 on success or error code otherwise.
+ */
+static int audio_tx_completion(struct most_interface *iface, int channel_id)
+{
+	struct channel *channel = get_channel(iface, channel_id);
+
+	if (!channel) {
+		pr_err("sound_tx_completion(), invalid channel %d\n",
+		       channel_id);
+		return -EINVAL;
+	}
+
+	wake_up_interruptible(&channel->playback_waitq);
+
+	return 0;
+}
+
+/**
+ * Initialization of the struct most_aim
+ */
+static struct most_aim audio_aim = {
+	.name = DRIVER_NAME,
+	.probe_channel = audio_probe_channel,
+	.disconnect_channel = audio_disconnect_channel,
+	.rx_completion = audio_rx_completion,
+	.tx_completion = audio_tx_completion,
+};
+
+static int __init audio_init(void)
+{
+	pr_info("init()\n");
+
+	INIT_LIST_HEAD(&dev_list);
+
+	return most_register_aim(&audio_aim);
+}
+
+static void __exit audio_exit(void)
+{
+	struct channel *channel, *tmp;
+
+	pr_info("exit()\n");
+
+	list_for_each_entry_safe(channel, tmp, &dev_list, list) {
+		list_del(&channel->list);
+		snd_card_free(channel->card);
+	}
+
+	most_deregister_aim(&audio_aim);
+}
+
+module_init(audio_init);
+module_exit(audio_exit);
+
+MODULE_LICENSE("GPL");
+MODULE_AUTHOR("Christian Gromm <christian.gromm@microchip.com>");
+MODULE_DESCRIPTION("Audio Application Interface Module for MostCore");