/*
   * Audio and Music Data Transmission Protocol (IEC 61883-6) streams
   * with Common Isochronous Packet (IEC 61883-1) headers
   *
   * Copyright (c) Clemens Ladisch <clemens@ladisch.de>
   * Licensed under the terms of the GNU General Public License, version 2.
   */
  
  #include <linux/device.h>
  #include <linux/err.h>
  #include <linux/firewire.h>
  #include <linux/module.h>
  #include <linux/slab.h>
  #include <sound/pcm.h>
  #include "amdtp.h"
  
  #define TICKS_PER_CYCLE		3072
  #define CYCLES_PER_SECOND	8000
  #define TICKS_PER_SECOND	(TICKS_PER_CYCLE * CYCLES_PER_SECOND)
  
  #define TRANSFER_DELAY_TICKS	0x2e00 /* 479.17 µs */
  
  #define TAG_CIP			1
  
  #define CIP_EOH			(1u << 31)
  #define CIP_FMT_AM		(0x10 << 24)
  #define AMDTP_FDF_AM824		(0 << 19)
  #define AMDTP_FDF_SFC_SHIFT	16
  
  /* TODO: make these configurable */
  #define INTERRUPT_INTERVAL	16
  #define QUEUE_LENGTH		48
  
  static void pcm_period_tasklet(unsigned long data);
  
  /**
   * amdtp_out_stream_init - initialize an AMDTP output stream structure
   * @s: the AMDTP output stream to initialize
   * @unit: the target of the stream
   * @flags: the packet transmission method to use
   */
  int amdtp_out_stream_init(struct amdtp_out_stream *s, struct fw_unit *unit,
  			  enum cip_out_flags flags)
  {
  	s->unit = fw_unit_get(unit);
  	s->flags = flags;
  	s->context = ERR_PTR(-1);
  	mutex_init(&s->mutex);
  	tasklet_init(&s->period_tasklet, pcm_period_tasklet, (unsigned long)s);
  	s->packet_index = 0;
  
  	return 0;
  }
  EXPORT_SYMBOL(amdtp_out_stream_init);
  
  /**
   * amdtp_out_stream_destroy - free stream resources
   * @s: the AMDTP output stream to destroy
   */
  void amdtp_out_stream_destroy(struct amdtp_out_stream *s)
  {
  	WARN_ON(amdtp_out_stream_running(s));
  	mutex_destroy(&s->mutex);
  	fw_unit_put(s->unit);
  }
  EXPORT_SYMBOL(amdtp_out_stream_destroy);
  
  const unsigned int amdtp_syt_intervals[CIP_SFC_COUNT] = {
  	[CIP_SFC_32000]  =  8,
  	[CIP_SFC_44100]  =  8,
  	[CIP_SFC_48000]  =  8,
  	[CIP_SFC_88200]  = 16,
  	[CIP_SFC_96000]  = 16,
  	[CIP_SFC_176400] = 32,
  	[CIP_SFC_192000] = 32,
  };
  EXPORT_SYMBOL(amdtp_syt_intervals);
  
  /**
   * amdtp_out_stream_set_parameters - set stream parameters
   * @s: the AMDTP output stream to configure
   * @rate: the sample rate
   * @pcm_channels: the number of PCM samples in each data block, to be encoded
   *                as AM824 multi-bit linear audio
   * @midi_ports: the number of MIDI ports (i.e., MPX-MIDI Data Channels)
   *
   * The parameters must be set before the stream is started, and must not be
   * changed while the stream is running.
   */
  void amdtp_out_stream_set_parameters(struct amdtp_out_stream *s,
  				     unsigned int rate,
  				     unsigned int pcm_channels,
  				     unsigned int midi_ports)
  {
  	static const unsigned int rates[] = {
  		[CIP_SFC_32000]  =  32000,
  		[CIP_SFC_44100]  =  44100,
  		[CIP_SFC_48000]  =  48000,
  		[CIP_SFC_88200]  =  88200,
  		[CIP_SFC_96000]  =  96000,
  		[CIP_SFC_176400] = 176400,
  		[CIP_SFC_192000] = 192000,
  	};
  	unsigned int sfc;
  
  	if (WARN_ON(amdtp_out_stream_running(s)))
  		return;
  
  	for (sfc = 0; sfc < CIP_SFC_COUNT; ++sfc)
  		if (rates[sfc] == rate)
  			goto sfc_found;
  	WARN_ON(1);
  	return;
  
  sfc_found:
  	s->dual_wire = (s->flags & CIP_HI_DUALWIRE) && sfc > CIP_SFC_96000;
  	if (s->dual_wire) {
  		sfc -= 2;
  		rate /= 2;
  		pcm_channels *= 2;
  	}
  	s->sfc = sfc;
  	s->data_block_quadlets = pcm_channels + DIV_ROUND_UP(midi_ports, 8);
  	s->pcm_channels = pcm_channels;
  	s->midi_ports = midi_ports;
  
  	s->syt_interval = amdtp_syt_intervals[sfc];
  
  	/* default buffering in the device */
  	s->transfer_delay = TRANSFER_DELAY_TICKS - TICKS_PER_CYCLE;
  	if (s->flags & CIP_BLOCKING)
  		/* additional buffering needed to adjust for no-data packets */
  		s->transfer_delay += TICKS_PER_SECOND * s->syt_interval / rate;
  }
  EXPORT_SYMBOL(amdtp_out_stream_set_parameters);
  
  /**
   * amdtp_out_stream_get_max_payload - get the stream's packet size
   * @s: the AMDTP output stream
   *
   * This function must not be called before the stream has been configured
   * with amdtp_out_stream_set_parameters().
   */
  unsigned int amdtp_out_stream_get_max_payload(struct amdtp_out_stream *s)
  {
  	return 8 + s->syt_interval * s->data_block_quadlets * 4;
  }
  EXPORT_SYMBOL(amdtp_out_stream_get_max_payload);
  
  static void amdtp_write_s16(struct amdtp_out_stream *s,
  			    struct snd_pcm_substream *pcm,
  			    __be32 *buffer, unsigned int frames);
  static void amdtp_write_s32(struct amdtp_out_stream *s,
  			    struct snd_pcm_substream *pcm,
  			    __be32 *buffer, unsigned int frames);
  static void amdtp_write_s16_dualwire(struct amdtp_out_stream *s,
  				     struct snd_pcm_substream *pcm,
  				     __be32 *buffer, unsigned int frames);
  static void amdtp_write_s32_dualwire(struct amdtp_out_stream *s,
  				     struct snd_pcm_substream *pcm,
  				     __be32 *buffer, unsigned int frames);
  
  /**
   * amdtp_out_stream_set_pcm_format - set the PCM format
   * @s: the AMDTP output stream to configure
   * @format: the format of the ALSA PCM device
   *
   * The sample format must be set after the other paramters (rate/PCM channels/
   * MIDI) and before the stream is started, and must not be changed while the
   * stream is running.
   */
  void amdtp_out_stream_set_pcm_format(struct amdtp_out_stream *s,
  				     snd_pcm_format_t format)
  {
  	if (WARN_ON(amdtp_out_stream_running(s)))
  		return;
  
  	switch (format) {
  	default:
  		WARN_ON(1);
  		/* fall through */
  	case SNDRV_PCM_FORMAT_S16:
  		if (s->dual_wire)
  			s->transfer_samples = amdtp_write_s16_dualwire;
  		else
  			s->transfer_samples = amdtp_write_s16;
  		break;
  	case SNDRV_PCM_FORMAT_S32:
  		if (s->dual_wire)
  			s->transfer_samples = amdtp_write_s32_dualwire;
  		else
  			s->transfer_samples = amdtp_write_s32;
  		break;
  	}
  }
  EXPORT_SYMBOL(amdtp_out_stream_set_pcm_format);
  
  /**
   * amdtp_out_stream_pcm_prepare - prepare PCM device for running
   * @s: the AMDTP output stream
   *
   * This function should be called from the PCM device's .prepare callback.
   */
  void amdtp_out_stream_pcm_prepare(struct amdtp_out_stream *s)
  {
  	tasklet_kill(&s->period_tasklet);
  	s->pcm_buffer_pointer = 0;
  	s->pcm_period_pointer = 0;
  	s->pointer_flush = true;
  }
  EXPORT_SYMBOL(amdtp_out_stream_pcm_prepare);
  
  static unsigned int calculate_data_blocks(struct amdtp_out_stream *s)
  {
  	unsigned int phase, data_blocks;
  
  	if (!cip_sfc_is_base_44100(s->sfc)) {
  		/* Sample_rate / 8000 is an integer, and precomputed. */
  		data_blocks = s->data_block_state;
  	} else {
  		phase = s->data_block_state;
  
  		/*
  		 * This calculates the number of data blocks per packet so that
  		 * 1) the overall rate is correct and exactly synchronized to
  		 *    the bus clock, and
  		 * 2) packets with a rounded-up number of blocks occur as early
  		 *    as possible in the sequence (to prevent underruns of the
  		 *    device's buffer).
  		 */
  		if (s->sfc == CIP_SFC_44100)
  			/* 6 6 5 6 5 6 5 ... */
  			data_blocks = 5 + ((phase & 1) ^
  					   (phase == 0 || phase >= 40));
  		else
  			/* 12 11 11 11 11 ... or 23 22 22 22 22 ... */
  			data_blocks = 11 * (s->sfc >> 1) + (phase == 0);
  		if (++phase >= (80 >> (s->sfc >> 1)))
  			phase = 0;
  		s->data_block_state = phase;
  	}
  
  	return data_blocks;
  }
  
  static unsigned int calculate_syt(struct amdtp_out_stream *s,
  				  unsigned int cycle)
  {
  	unsigned int syt_offset, phase, index, syt;
  
  	if (s->last_syt_offset < TICKS_PER_CYCLE) {
  		if (!cip_sfc_is_base_44100(s->sfc))
  			syt_offset = s->last_syt_offset + s->syt_offset_state;
  		else {
  		/*
  		 * The time, in ticks, of the n'th SYT_INTERVAL sample is:
  		 *   n * SYT_INTERVAL * 24576000 / sample_rate
  		 * Modulo TICKS_PER_CYCLE, the difference between successive
  		 * elements is about 1386.23.  Rounding the results of this
  		 * formula to the SYT precision results in a sequence of
  		 * differences that begins with:
  		 *   1386 1386 1387 1386 1386 1386 1387 1386 1386 1386 1387 ...
  		 * This code generates _exactly_ the same sequence.
  		 */
  			phase = s->syt_offset_state;
  			index = phase % 13;
  			syt_offset = s->last_syt_offset;
  			syt_offset += 1386 + ((index && !(index & 3)) ||
  					      phase == 146);
  			if (++phase >= 147)
  				phase = 0;
  			s->syt_offset_state = phase;
  		}
  	} else
  		syt_offset = s->last_syt_offset - TICKS_PER_CYCLE;
  	s->last_syt_offset = syt_offset;
  
  	if (syt_offset < TICKS_PER_CYCLE) {
  		syt_offset += s->transfer_delay;
  		syt = (cycle + syt_offset / TICKS_PER_CYCLE) << 12;
  		syt += syt_offset % TICKS_PER_CYCLE;
  
  		return syt & 0xffff;
  	} else {
  		return 0xffff; /* no info */
  	}
  }
  
  static void amdtp_write_s32(struct amdtp_out_stream *s,
  			    struct snd_pcm_substream *pcm,
  			    __be32 *buffer, unsigned int frames)
  {
  	struct snd_pcm_runtime *runtime = pcm->runtime;
  	unsigned int channels, remaining_frames, frame_step, i, c;
  	const u32 *src;
  
  	channels = s->pcm_channels;
  	src = (void *)runtime->dma_area +
  			frames_to_bytes(runtime, s->pcm_buffer_pointer);
  	remaining_frames = runtime->buffer_size - s->pcm_buffer_pointer;
  	frame_step = s->data_block_quadlets - channels;
  
  	for (i = 0; i < frames; ++i) {
  		for (c = 0; c < channels; ++c) {
  			*buffer = cpu_to_be32((*src >> 8) | 0x40000000);
  			src++;
  			buffer++;
  		}
  		buffer += frame_step;
  		if (--remaining_frames == 0)
  			src = (void *)runtime->dma_area;
  	}
  }
  
  static void amdtp_write_s16(struct amdtp_out_stream *s,
  			    struct snd_pcm_substream *pcm,
  			    __be32 *buffer, unsigned int frames)
  {
  	struct snd_pcm_runtime *runtime = pcm->runtime;
  	unsigned int channels, remaining_frames, frame_step, i, c;
  	const u16 *src;
  
  	channels = s->pcm_channels;
  	src = (void *)runtime->dma_area +
  			frames_to_bytes(runtime, s->pcm_buffer_pointer);
  	remaining_frames = runtime->buffer_size - s->pcm_buffer_pointer;
  	frame_step = s->data_block_quadlets - channels;
  
  	for (i = 0; i < frames; ++i) {
  		for (c = 0; c < channels; ++c) {
  			*buffer = cpu_to_be32((*src << 8) | 0x40000000);
  			src++;
  			buffer++;
  		}
  		buffer += frame_step;
  		if (--remaining_frames == 0)
  			src = (void *)runtime->dma_area;
  	}
  }
  
  static void amdtp_write_s32_dualwire(struct amdtp_out_stream *s,
  				     struct snd_pcm_substream *pcm,
  				     __be32 *buffer, unsigned int frames)
  {
  	struct snd_pcm_runtime *runtime = pcm->runtime;
  	unsigned int channels, frame_adjust_1, frame_adjust_2, i, c;
  	const u32 *src;
  
  	channels = s->pcm_channels;
  	src = (void *)runtime->dma_area +
  			s->pcm_buffer_pointer * (runtime->frame_bits / 8);
  	frame_adjust_1 = channels - 1;
  	frame_adjust_2 = 1 - (s->data_block_quadlets - channels);
  
  	channels /= 2;
  	for (i = 0; i < frames; ++i) {
  		for (c = 0; c < channels; ++c) {
  			*buffer = cpu_to_be32((*src >> 8) | 0x40000000);
  			src++;
  			buffer += 2;
  		}
  		buffer -= frame_adjust_1;
  		for (c = 0; c < channels; ++c) {
  			*buffer = cpu_to_be32((*src >> 8) | 0x40000000);
  			src++;
  			buffer += 2;
  		}
  		buffer -= frame_adjust_2;
  	}
  }
  
  static void amdtp_write_s16_dualwire(struct amdtp_out_stream *s,
  				     struct snd_pcm_substream *pcm,
  				     __be32 *buffer, unsigned int frames)
  {
  	struct snd_pcm_runtime *runtime = pcm->runtime;
  	unsigned int channels, frame_adjust_1, frame_adjust_2, i, c;
  	const u16 *src;
  
  	channels = s->pcm_channels;
  	src = (void *)runtime->dma_area +
  			s->pcm_buffer_pointer * (runtime->frame_bits / 8);
  	frame_adjust_1 = channels - 1;
  	frame_adjust_2 = 1 - (s->data_block_quadlets - channels);
  
  	channels /= 2;
  	for (i = 0; i < frames; ++i) {
  		for (c = 0; c < channels; ++c) {
  			*buffer = cpu_to_be32((*src << 8) | 0x40000000);
  			src++;
  			buffer += 2;
  		}
  		buffer -= frame_adjust_1;
  		for (c = 0; c < channels; ++c) {
  			*buffer = cpu_to_be32((*src << 8) | 0x40000000);
  			src++;
  			buffer += 2;
  		}
  		buffer -= frame_adjust_2;
  	}
  }
  
  static void amdtp_fill_pcm_silence(struct amdtp_out_stream *s,
  				   __be32 *buffer, unsigned int frames)
  {
  	unsigned int i, c;
  
  	for (i = 0; i < frames; ++i) {
  		for (c = 0; c < s->pcm_channels; ++c)
  			buffer[c] = cpu_to_be32(0x40000000);
  		buffer += s->data_block_quadlets;
  	}
  }
  
  static void amdtp_fill_midi(struct amdtp_out_stream *s,
  			    __be32 *buffer, unsigned int frames)
  {
  	unsigned int i;
  
  	for (i = 0; i < frames; ++i)
  		buffer[s->pcm_channels + i * s->data_block_quadlets] =
  						cpu_to_be32(0x80000000);
  }
  
  static void queue_out_packet(struct amdtp_out_stream *s, unsigned int cycle)
  {
  	__be32 *buffer;
  	unsigned int index, data_blocks, syt, ptr;
  	struct snd_pcm_substream *pcm;
  	struct fw_iso_packet packet;
  	int err;
  
  	if (s->packet_index < 0)
  		return;
  	index = s->packet_index;
  
  	/* this module generate empty packet for 'no data' */
  	syt = calculate_syt(s, cycle);
  	if (!(s->flags & CIP_BLOCKING))
  		data_blocks = calculate_data_blocks(s);
  	else if (syt != 0xffff)
  		data_blocks = s->syt_interval;
  	else
  		data_blocks = 0;
  
  	buffer = s->buffer.packets[index].buffer;
  	buffer[0] = cpu_to_be32(ACCESS_ONCE(s->source_node_id_field) |
  				(s->data_block_quadlets << 16) |
  				s->data_block_counter);
  	buffer[1] = cpu_to_be32(CIP_EOH | CIP_FMT_AM | AMDTP_FDF_AM824 |
  				(s->sfc << AMDTP_FDF_SFC_SHIFT) | syt);
  	buffer += 2;
  
  	pcm = ACCESS_ONCE(s->pcm);
  	if (pcm)
  		s->transfer_samples(s, pcm, buffer, data_blocks);
  	else
  		amdtp_fill_pcm_silence(s, buffer, data_blocks);
  	if (s->midi_ports)
  		amdtp_fill_midi(s, buffer, data_blocks);
  
  	s->data_block_counter = (s->data_block_counter + data_blocks) & 0xff;
  
  	packet.payload_length = 8 + data_blocks * 4 * s->data_block_quadlets;
  	packet.interrupt = IS_ALIGNED(index + 1, INTERRUPT_INTERVAL);
  	packet.skip = 0;
  	packet.tag = TAG_CIP;
  	packet.sy = 0;
  	packet.header_length = 0;
  
  	err = fw_iso_context_queue(s->context, &packet, &s->buffer.iso_buffer,
  				   s->buffer.packets[index].offset);
  	if (err < 0) {
  		dev_err(&s->unit->device, "queueing error: %d
  ", err);
  		s->packet_index = -1;
  		amdtp_out_stream_pcm_abort(s);
  		return;
  	}
  
  	if (++index >= QUEUE_LENGTH)
  		index = 0;
  	s->packet_index = index;
  
  	if (pcm) {
  		if (s->dual_wire)
  			data_blocks *= 2;
  
  		ptr = s->pcm_buffer_pointer + data_blocks;
  		if (ptr >= pcm->runtime->buffer_size)
  			ptr -= pcm->runtime->buffer_size;
  		ACCESS_ONCE(s->pcm_buffer_pointer) = ptr;
  
  		s->pcm_period_pointer += data_blocks;
  		if (s->pcm_period_pointer >= pcm->runtime->period_size) {
  			s->pcm_period_pointer -= pcm->runtime->period_size;
  			s->pointer_flush = false;
  			tasklet_hi_schedule(&s->period_tasklet);
  		}
  	}
  }
  
  static void pcm_period_tasklet(unsigned long data)
  {
  	struct amdtp_out_stream *s = (void *)data;
  	struct snd_pcm_substream *pcm = ACCESS_ONCE(s->pcm);
  
  	if (pcm)
  		snd_pcm_period_elapsed(pcm);
  }
  
  static void out_packet_callback(struct fw_iso_context *context, u32 cycle,
  				size_t header_length, void *header, void *data)
  {
  	struct amdtp_out_stream *s = data;
  	unsigned int i, packets = header_length / 4;
  
  	/*
  	 * Compute the cycle of the last queued packet.
  	 * (We need only the four lowest bits for the SYT, so we can ignore
  	 * that bits 0-11 must wrap around at 3072.)
  	 */
  	cycle += QUEUE_LENGTH - packets;
  
  	for (i = 0; i < packets; ++i)
  		queue_out_packet(s, ++cycle);
  	fw_iso_context_queue_flush(s->context);
  }
  
  static int queue_initial_skip_packets(struct amdtp_out_stream *s)
  {
  	struct fw_iso_packet skip_packet = {
  		.skip = 1,
  	};
  	unsigned int i;
  	int err;
  
  	for (i = 0; i < QUEUE_LENGTH; ++i) {
  		skip_packet.interrupt = IS_ALIGNED(s->packet_index + 1,
  						   INTERRUPT_INTERVAL);
  		err = fw_iso_context_queue(s->context, &skip_packet, NULL, 0);
  		if (err < 0)
  			return err;
  		if (++s->packet_index >= QUEUE_LENGTH)
  			s->packet_index = 0;
  	}
  
  	return 0;
  }
  
  /**
   * amdtp_out_stream_start - start sending packets
   * @s: the AMDTP output stream to start
   * @channel: the isochronous channel on the bus
   * @speed: firewire speed code
   *
   * The stream cannot be started until it has been configured with
   * amdtp_out_stream_set_parameters() and amdtp_out_stream_set_pcm_format(),
   * and it must be started before any PCM or MIDI device can be started.
   */
  int amdtp_out_stream_start(struct amdtp_out_stream *s, int channel, int speed)
  {
  	static const struct {
  		unsigned int data_block;
  		unsigned int syt_offset;
  	} initial_state[] = {
  		[CIP_SFC_32000]  = {  4, 3072 },
  		[CIP_SFC_48000]  = {  6, 1024 },
  		[CIP_SFC_96000]  = { 12, 1024 },
  		[CIP_SFC_192000] = { 24, 1024 },
  		[CIP_SFC_44100]  = {  0,   67 },
  		[CIP_SFC_88200]  = {  0,   67 },
  		[CIP_SFC_176400] = {  0,   67 },
  	};
  	int err;
  
  	mutex_lock(&s->mutex);
  
  	if (WARN_ON(amdtp_out_stream_running(s) ||
  		    (!s->pcm_channels && !s->midi_ports))) {
  		err = -EBADFD;
  		goto err_unlock;
  	}
  
  	s->data_block_state = initial_state[s->sfc].data_block;
  	s->syt_offset_state = initial_state[s->sfc].syt_offset;
  	s->last_syt_offset = TICKS_PER_CYCLE;
  
  	err = iso_packets_buffer_init(&s->buffer, s->unit, QUEUE_LENGTH,
  				      amdtp_out_stream_get_max_payload(s),
  				      DMA_TO_DEVICE);
  	if (err < 0)
  		goto err_unlock;
  
  	s->context = fw_iso_context_create(fw_parent_device(s->unit)->card,
  					   FW_ISO_CONTEXT_TRANSMIT,
  					   channel, speed, 0,
  					   out_packet_callback, s);
  	if (IS_ERR(s->context)) {
  		err = PTR_ERR(s->context);
  		if (err == -EBUSY)
  			dev_err(&s->unit->device,
  				"no free output stream on this controller
  ");
  		goto err_buffer;
  	}
  
  	amdtp_out_stream_update(s);
  
  	s->packet_index = 0;
  	s->data_block_counter = 0;
  	err = queue_initial_skip_packets(s);
  	if (err < 0)
  		goto err_context;
  
  	err = fw_iso_context_start(s->context, -1, 0, 0);
  	if (err < 0)
  		goto err_context;
  
  	mutex_unlock(&s->mutex);
  
  	return 0;
  
  err_context:
  	fw_iso_context_destroy(s->context);
  	s->context = ERR_PTR(-1);
  err_buffer:
  	iso_packets_buffer_destroy(&s->buffer, s->unit);
  err_unlock:
  	mutex_unlock(&s->mutex);
  
  	return err;
  }
  EXPORT_SYMBOL(amdtp_out_stream_start);
  
  /**
   * amdtp_out_stream_pcm_pointer - get the PCM buffer position
   * @s: the AMDTP output stream that transports the PCM data
   *
   * Returns the current buffer position, in frames.
   */
  unsigned long amdtp_out_stream_pcm_pointer(struct amdtp_out_stream *s)
  {
  	/* this optimization is allowed to be racy */
  	if (s->pointer_flush)
  		fw_iso_context_flush_completions(s->context);
  	else
  		s->pointer_flush = true;
  
  	return ACCESS_ONCE(s->pcm_buffer_pointer);
  }
  EXPORT_SYMBOL(amdtp_out_stream_pcm_pointer);
  
  /**
   * amdtp_out_stream_update - update the stream after a bus reset
   * @s: the AMDTP output stream
   */
  void amdtp_out_stream_update(struct amdtp_out_stream *s)
  {
  	ACCESS_ONCE(s->source_node_id_field) =
  		(fw_parent_device(s->unit)->card->node_id & 0x3f) << 24;
  }
  EXPORT_SYMBOL(amdtp_out_stream_update);
  
  /**
   * amdtp_out_stream_stop - stop sending packets
   * @s: the AMDTP output stream to stop
   *
   * All PCM and MIDI devices of the stream must be stopped before the stream
   * itself can be stopped.
   */
  void amdtp_out_stream_stop(struct amdtp_out_stream *s)
  {
  	mutex_lock(&s->mutex);
  
  	if (!amdtp_out_stream_running(s)) {
  		mutex_unlock(&s->mutex);
  		return;
  	}
  
  	tasklet_kill(&s->period_tasklet);
  	fw_iso_context_stop(s->context);
  	fw_iso_context_destroy(s->context);
  	s->context = ERR_PTR(-1);
  	iso_packets_buffer_destroy(&s->buffer, s->unit);
  
  	mutex_unlock(&s->mutex);
  }
  EXPORT_SYMBOL(amdtp_out_stream_stop);
  
  /**
   * amdtp_out_stream_pcm_abort - abort the running PCM device
   * @s: the AMDTP stream about to be stopped
   *
   * If the isochronous stream needs to be stopped asynchronously, call this
   * function first to stop the PCM device.
   */
  void amdtp_out_stream_pcm_abort(struct amdtp_out_stream *s)
  {
  	struct snd_pcm_substream *pcm;
  
  	pcm = ACCESS_ONCE(s->pcm);
  	if (pcm) {
  		snd_pcm_stream_lock_irq(pcm);
  		if (snd_pcm_running(pcm))
  			snd_pcm_stop(pcm, SNDRV_PCM_STATE_XRUN);
  		snd_pcm_stream_unlock_irq(pcm);
  	}
  }
  EXPORT_SYMBOL(amdtp_out_stream_pcm_abort);