sound/firewire/amdtp-am824.c - third_party/kernel - Git at Google

 // SPDX-License-Identifier: GPL-2.0-only
 /*
  * AM824 format in Audio and Music Data Transmission Protocol (IEC 61883-6)
  *
  * Copyright (c) Clemens Ladisch <clemens@ladisch.de>
  * Copyright (c) 2015 Takashi Sakamoto <o-takashi@sakamocchi.jp>
  */

 #include <linux/slab.h>

 #include "amdtp-am824.h"

 #define CIP_FMT_AM		0x10

 /* "Clock-based rate control mode" is just supported. */
 #define AMDTP_FDF_AM824		0x00

 /*
  * Nominally 3125 bytes/second, but the MIDI port's clock might be
  * 1% too slow, and the bus clock 100 ppm too fast.
  */
 #define MIDI_BYTES_PER_SECOND	3093

 /*
  * Several devices look only at the first eight data blocks.
  * In any case, this is more than enough for the MIDI data rate.
  */
 #define MAX_MIDI_RX_BLOCKS	8

 struct amdtp_am824 {
 	struct snd_rawmidi_substream *midi[AM824_MAX_CHANNELS_FOR_MIDI * 8];
 	int midi_fifo_limit;
 	int midi_fifo_used[AM824_MAX_CHANNELS_FOR_MIDI * 8];
 	unsigned int pcm_channels;
 	unsigned int midi_ports;

 	u8 pcm_positions[AM824_MAX_CHANNELS_FOR_PCM];
 	u8 midi_position;

 	unsigned int frame_multiplier;
 };

 /**
  * amdtp_am824_set_parameters - set stream parameters
  * @s: the AMDTP 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)
  * @double_pcm_frames: one data block transfers two PCM frames
  *
  * The parameters must be set before the stream is started, and must not be
  * changed while the stream is running.
  */
 int amdtp_am824_set_parameters(struct amdtp_stream *s, unsigned int rate,
 			       unsigned int pcm_channels,
 			       unsigned int midi_ports,
 			       bool double_pcm_frames)
 {
 	struct amdtp_am824 *p = s->protocol;
 	unsigned int midi_channels;
 	unsigned int i;
 	int err;

 	if (amdtp_stream_running(s))
 		return -EINVAL;

 	if (pcm_channels > AM824_MAX_CHANNELS_FOR_PCM)
 		return -EINVAL;

 	midi_channels = DIV_ROUND_UP(midi_ports, 8);
 	if (midi_channels > AM824_MAX_CHANNELS_FOR_MIDI)
 		return -EINVAL;

 	if (WARN_ON(amdtp_stream_running(s)) ||
 	    WARN_ON(pcm_channels > AM824_MAX_CHANNELS_FOR_PCM) ||
 	    WARN_ON(midi_channels > AM824_MAX_CHANNELS_FOR_MIDI))
 		return -EINVAL;

 	err = amdtp_stream_set_parameters(s, rate,
 					  pcm_channels + midi_channels);
 	if (err < 0)
 		return err;

 	if (s->direction == AMDTP_OUT_STREAM)
 		s->ctx_data.rx.fdf = AMDTP_FDF_AM824 | s->sfc;

 	p->pcm_channels = pcm_channels;
 	p->midi_ports = midi_ports;

 	/*
 	 * In IEC 61883-6, one data block represents one event. In ALSA, one
 	 * event equals to one PCM frame. But Dice has a quirk at higher
 	 * sampling rate to transfer two PCM frames in one data block.
 	 */
 	if (double_pcm_frames)
 		p->frame_multiplier = 2;
 	else
 		p->frame_multiplier = 1;

 	/* init the position map for PCM and MIDI channels */
 	for (i = 0; i < pcm_channels; i++)
 		p->pcm_positions[i] = i;
 	p->midi_position = p->pcm_channels;

 	/*
 	 * We do not know the actual MIDI FIFO size of most devices.  Just
 	 * assume two bytes, i.e., one byte can be received over the bus while
 	 * the previous one is transmitted over MIDI.
 	 * (The value here is adjusted for midi_ratelimit_per_packet().)
 	 */
 	p->midi_fifo_limit = rate - MIDI_BYTES_PER_SECOND * s->syt_interval + 1;

 	return 0;
 }
 EXPORT_SYMBOL_GPL(amdtp_am824_set_parameters);

 /**
  * amdtp_am824_set_pcm_position - set an index of data channel for a channel
  *				  of PCM frame
  * @s: the AMDTP stream
  * @index: the index of data channel in an data block
  * @position: the channel of PCM frame
  */
 void amdtp_am824_set_pcm_position(struct amdtp_stream *s, unsigned int index,
 				 unsigned int position)
 {
 	struct amdtp_am824 *p = s->protocol;

 	if (index < p->pcm_channels)
 		p->pcm_positions[index] = position;
 }
 EXPORT_SYMBOL_GPL(amdtp_am824_set_pcm_position);

 /**
  * amdtp_am824_set_midi_position - set a index of data channel for MIDI
  *				   conformant data channel
  * @s: the AMDTP stream
  * @position: the index of data channel in an data block
  */
 void amdtp_am824_set_midi_position(struct amdtp_stream *s,
 				   unsigned int position)
 {
 	struct amdtp_am824 *p = s->protocol;

 	p->midi_position = position;
 }
 EXPORT_SYMBOL_GPL(amdtp_am824_set_midi_position);

 static void write_pcm_s32(struct amdtp_stream *s, struct snd_pcm_substream *pcm,
 			  __be32 *buffer, unsigned int frames,
 			  unsigned int pcm_frames)
 {
 	struct amdtp_am824 *p = s->protocol;
 	unsigned int channels = p->pcm_channels;
 	struct snd_pcm_runtime *runtime = pcm->runtime;
 	unsigned int pcm_buffer_pointer;
 	int remaining_frames;
 	const u32 *src;
 	int i, c;

 	pcm_buffer_pointer = s->pcm_buffer_pointer + pcm_frames;
 	pcm_buffer_pointer %= runtime->buffer_size;

 	src = (void *)runtime->dma_area +
 				frames_to_bytes(runtime, pcm_buffer_pointer);
 	remaining_frames = runtime->buffer_size - pcm_buffer_pointer;

 	for (i = 0; i < frames; ++i) {
 		for (c = 0; c < channels; ++c) {
 			buffer[p->pcm_positions[c]] =
 					cpu_to_be32((*src >> 8) | 0x40000000);
 			src++;
 		}
 		buffer += s->data_block_quadlets;
 		if (--remaining_frames == 0)
 			src = (void *)runtime->dma_area;
 	}
 }

 static void read_pcm_s32(struct amdtp_stream *s, struct snd_pcm_substream *pcm,
 			 __be32 *buffer, unsigned int frames,
 			 unsigned int pcm_frames)
 {
 	struct amdtp_am824 *p = s->protocol;
 	unsigned int channels = p->pcm_channels;
 	struct snd_pcm_runtime *runtime = pcm->runtime;
 	unsigned int pcm_buffer_pointer;
 	int remaining_frames;
 	u32 *dst;
 	int i, c;

 	pcm_buffer_pointer = s->pcm_buffer_pointer + pcm_frames;
 	pcm_buffer_pointer %= runtime->buffer_size;

 	dst  = (void *)runtime->dma_area +
 				frames_to_bytes(runtime, pcm_buffer_pointer);
 	remaining_frames = runtime->buffer_size - pcm_buffer_pointer;

 	for (i = 0; i < frames; ++i) {
 		for (c = 0; c < channels; ++c) {
 			*dst = be32_to_cpu(buffer[p->pcm_positions[c]]) << 8;
 			dst++;
 		}
 		buffer += s->data_block_quadlets;
 		if (--remaining_frames == 0)
 			dst = (void *)runtime->dma_area;
 	}
 }

 static void write_pcm_silence(struct amdtp_stream *s,
 			      __be32 *buffer, unsigned int frames)
 {
 	struct amdtp_am824 *p = s->protocol;
 	unsigned int i, c, channels = p->pcm_channels;

 	for (i = 0; i < frames; ++i) {
 		for (c = 0; c < channels; ++c)
 			buffer[p->pcm_positions[c]] = cpu_to_be32(0x40000000);
 		buffer += s->data_block_quadlets;
 	}
 }

 /**
  * amdtp_am824_add_pcm_hw_constraints - add hw constraints for PCM substream
  * @s:		the AMDTP stream for AM824 data block, must be initialized.
  * @runtime:	the PCM substream runtime
  *
  */
 int amdtp_am824_add_pcm_hw_constraints(struct amdtp_stream *s,
 				       struct snd_pcm_runtime *runtime)
 {
 	int err;

 	err = amdtp_stream_add_pcm_hw_constraints(s, runtime);
 	if (err < 0)
 		return err;

 	/* AM824 in IEC 61883-6 can deliver 24bit data. */
 	return snd_pcm_hw_constraint_msbits(runtime, 0, 32, 24);
 }
 EXPORT_SYMBOL_GPL(amdtp_am824_add_pcm_hw_constraints);

 /**
  * amdtp_am824_midi_trigger - start/stop playback/capture with a MIDI device
  * @s: the AMDTP stream
  * @port: index of MIDI port
  * @midi: the MIDI device to be started, or %NULL to stop the current device
  *
  * Call this function on a running isochronous stream to enable the actual
  * transmission of MIDI data.  This function should be called from the MIDI
  * device's .trigger callback.
  */
 void amdtp_am824_midi_trigger(struct amdtp_stream *s, unsigned int port,
 			      struct snd_rawmidi_substream *midi)
 {
 	struct amdtp_am824 *p = s->protocol;

 	if (port < p->midi_ports)
 		WRITE_ONCE(p->midi[port], midi);
 }
 EXPORT_SYMBOL_GPL(amdtp_am824_midi_trigger);

 /*
  * To avoid sending MIDI bytes at too high a rate, assume that the receiving
  * device has a FIFO, and track how much it is filled.  This values increases
  * by one whenever we send one byte in a packet, but the FIFO empties at
  * a constant rate independent of our packet rate.  One packet has syt_interval
  * samples, so the number of bytes that empty out of the FIFO, per packet(!),
  * is MIDI_BYTES_PER_SECOND * syt_interval / sample_rate.  To avoid storing
  * fractional values, the values in midi_fifo_used[] are measured in bytes
  * multiplied by the sample rate.
  */
 static bool midi_ratelimit_per_packet(struct amdtp_stream *s, unsigned int port)
 {
 	struct amdtp_am824 *p = s->protocol;
 	int used;

 	used = p->midi_fifo_used[port];
 	if (used == 0) /* common shortcut */
 		return true;

 	used -= MIDI_BYTES_PER_SECOND * s->syt_interval;
 	used = max(used, 0);
 	p->midi_fifo_used[port] = used;

 	return used < p->midi_fifo_limit;
 }

 static void midi_rate_use_one_byte(struct amdtp_stream *s, unsigned int port)
 {
 	struct amdtp_am824 *p = s->protocol;

 	p->midi_fifo_used[port] += amdtp_rate_table[s->sfc];
 }

 static void write_midi_messages(struct amdtp_stream *s, __be32 *buffer,
 			unsigned int frames, unsigned int data_block_counter)
 {
 	struct amdtp_am824 *p = s->protocol;
 	unsigned int f, port;
 	u8 *b;

 	for (f = 0; f < frames; f++) {
 		b = (u8 *)&buffer[p->midi_position];

 		port = (data_block_counter + f) % 8;
 		if (f < MAX_MIDI_RX_BLOCKS &&
 		    midi_ratelimit_per_packet(s, port) &&
 		    p->midi[port] != NULL &&
 		    snd_rawmidi_transmit(p->midi[port], &b[1], 1) == 1) {
 			midi_rate_use_one_byte(s, port);
 			b[0] = 0x81;
 		} else {
 			b[0] = 0x80;
 			b[1] = 0;
 		}
 		b[2] = 0;
 		b[3] = 0;

 		buffer += s->data_block_quadlets;
 	}
 }

 static void read_midi_messages(struct amdtp_stream *s, __be32 *buffer,
 			unsigned int frames, unsigned int data_block_counter)
 {
 	struct amdtp_am824 *p = s->protocol;
 	int len;
 	u8 *b;
 	int f;

 	for (f = 0; f < frames; f++) {
 		unsigned int port = f;

 		if (!(s->flags & CIP_UNALIGHED_DBC))
 			port += data_block_counter;
 		port %= 8;
 		b = (u8 *)&buffer[p->midi_position];

 		len = b[0] - 0x80;
 		if ((1 <= len) &&  (len <= 3) && (p->midi[port]))
 			snd_rawmidi_receive(p->midi[port], b + 1, len);

 		buffer += s->data_block_quadlets;
 	}
 }

 static unsigned int process_it_ctx_payloads(struct amdtp_stream *s,
 					    const struct pkt_desc *descs,
 					    unsigned int packets,
 					    struct snd_pcm_substream *pcm)
 {
 	struct amdtp_am824 *p = s->protocol;
 	unsigned int pcm_frames = 0;
 	int i;

 	for (i = 0; i < packets; ++i) {
 		const struct pkt_desc *desc = descs + i;
 		__be32 *buf = desc->ctx_payload;
 		unsigned int data_blocks = desc->data_blocks;

 		if (pcm) {
 			write_pcm_s32(s, pcm, buf, data_blocks, pcm_frames);
 			pcm_frames += data_blocks * p->frame_multiplier;
 		} else {
 			write_pcm_silence(s, buf, data_blocks);
 		}

 		if (p->midi_ports) {
 			write_midi_messages(s, buf, data_blocks,
 					    desc->data_block_counter);
 		}
 	}

 	return pcm_frames;
 }

 static unsigned int process_ir_ctx_payloads(struct amdtp_stream *s,
 					    const struct pkt_desc *descs,
 					    unsigned int packets,
 					    struct snd_pcm_substream *pcm)
 {
 	struct amdtp_am824 *p = s->protocol;
 	unsigned int pcm_frames = 0;
 	int i;

 	for (i = 0; i < packets; ++i) {
 		const struct pkt_desc *desc = descs + i;
 		__be32 *buf = desc->ctx_payload;
 		unsigned int data_blocks = desc->data_blocks;

 		if (pcm) {
 			read_pcm_s32(s, pcm, buf, data_blocks, pcm_frames);
 			pcm_frames += data_blocks * p->frame_multiplier;
 		}

 		if (p->midi_ports) {
 			read_midi_messages(s, buf, data_blocks,
 					   desc->data_block_counter);
 		}
 	}

 	return pcm_frames;
 }

 /**
  * amdtp_am824_init - initialize an AMDTP stream structure to handle AM824
  *		      data block
  * @s: the AMDTP stream to initialize
  * @unit: the target of the stream
  * @dir: the direction of stream
  * @flags: the packet transmission method to use
  */
 int amdtp_am824_init(struct amdtp_stream *s, struct fw_unit *unit,
 		     enum amdtp_stream_direction dir, enum cip_flags flags)
 {
 	amdtp_stream_process_ctx_payloads_t process_ctx_payloads;

 	if (dir == AMDTP_IN_STREAM)
 		process_ctx_payloads = process_ir_ctx_payloads;
 	else
 		process_ctx_payloads = process_it_ctx_payloads;

 	return amdtp_stream_init(s, unit, dir, flags, CIP_FMT_AM,
 			process_ctx_payloads, sizeof(struct amdtp_am824));
 }
 EXPORT_SYMBOL_GPL(amdtp_am824_init);
	// SPDX-License-Identifier: GPL-2.0-only
	/*
	* AM824 format in Audio and Music Data Transmission Protocol (IEC 61883-6)
	*
	* Copyright (c) Clemens Ladisch <clemens@ladisch.de>
	* Copyright (c) 2015 Takashi Sakamoto <o-takashi@sakamocchi.jp>
	*/

	#include <linux/slab.h>

	#include "amdtp-am824.h"

	#define CIP_FMT_AM 0x10

	/* "Clock-based rate control mode" is just supported. */
	#define AMDTP_FDF_AM824 0x00

	/*
	* Nominally 3125 bytes/second, but the MIDI port's clock might be
	* 1% too slow, and the bus clock 100 ppm too fast.
	*/
	#define MIDI_BYTES_PER_SECOND 3093

	/*
	* Several devices look only at the first eight data blocks.
	* In any case, this is more than enough for the MIDI data rate.
	*/
	#define MAX_MIDI_RX_BLOCKS 8

	struct amdtp_am824 {
	struct snd_rawmidi_substream midi[AM824_MAX_CHANNELS_FOR_MIDI 8];
	int midi_fifo_limit;
	int midi_fifo_used[AM824_MAX_CHANNELS_FOR_MIDI * 8];
	unsigned int pcm_channels;
	unsigned int midi_ports;

	u8 pcm_positions[AM824_MAX_CHANNELS_FOR_PCM];
	u8 midi_position;

	unsigned int frame_multiplier;
	};

	/**
	* amdtp_am824_set_parameters - set stream parameters
	* @s: the AMDTP 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)
	* @double_pcm_frames: one data block transfers two PCM frames
	*
	* The parameters must be set before the stream is started, and must not be
	* changed while the stream is running.
	*/
	int amdtp_am824_set_parameters(struct amdtp_stream *s, unsigned int rate,
	unsigned int pcm_channels,
	unsigned int midi_ports,
	bool double_pcm_frames)
	{
	struct amdtp_am824 *p = s->protocol;
	unsigned int midi_channels;
	unsigned int i;
	int err;

	if (amdtp_stream_running(s))
	return -EINVAL;

	if (pcm_channels > AM824_MAX_CHANNELS_FOR_PCM)
	return -EINVAL;

	midi_channels = DIV_ROUND_UP(midi_ports, 8);
	if (midi_channels > AM824_MAX_CHANNELS_FOR_MIDI)
	return -EINVAL;

	if (WARN_ON(amdtp_stream_running(s)) \|\|
	WARN_ON(pcm_channels > AM824_MAX_CHANNELS_FOR_PCM) \|\|
	WARN_ON(midi_channels > AM824_MAX_CHANNELS_FOR_MIDI))
	return -EINVAL;

	err = amdtp_stream_set_parameters(s, rate,
	pcm_channels + midi_channels);
	if (err < 0)
	return err;

	if (s->direction == AMDTP_OUT_STREAM)
	s->ctx_data.rx.fdf = AMDTP_FDF_AM824 \| s->sfc;

	p->pcm_channels = pcm_channels;
	p->midi_ports = midi_ports;

	/*
	* In IEC 61883-6, one data block represents one event. In ALSA, one
	* event equals to one PCM frame. But Dice has a quirk at higher
	* sampling rate to transfer two PCM frames in one data block.
	*/
	if (double_pcm_frames)
	p->frame_multiplier = 2;
	else
	p->frame_multiplier = 1;

	/* init the position map for PCM and MIDI channels */
	for (i = 0; i < pcm_channels; i++)
	p->pcm_positions[i] = i;
	p->midi_position = p->pcm_channels;

	/*
	* We do not know the actual MIDI FIFO size of most devices. Just
	* assume two bytes, i.e., one byte can be received over the bus while
	* the previous one is transmitted over MIDI.
	* (The value here is adjusted for midi_ratelimit_per_packet().)
	*/
	p->midi_fifo_limit = rate - MIDI_BYTES_PER_SECOND * s->syt_interval + 1;

	return 0;
	}
	EXPORT_SYMBOL_GPL(amdtp_am824_set_parameters);

	/**
	* amdtp_am824_set_pcm_position - set an index of data channel for a channel
	* of PCM frame
	* @s: the AMDTP stream
	* @index: the index of data channel in an data block
	* @position: the channel of PCM frame
	*/
	void amdtp_am824_set_pcm_position(struct amdtp_stream *s, unsigned int index,
	unsigned int position)
	{
	struct amdtp_am824 *p = s->protocol;

	if (index < p->pcm_channels)
	p->pcm_positions[index] = position;
	}
	EXPORT_SYMBOL_GPL(amdtp_am824_set_pcm_position);

	/**
	* amdtp_am824_set_midi_position - set a index of data channel for MIDI
	* conformant data channel
	* @s: the AMDTP stream
	* @position: the index of data channel in an data block
	*/
	void amdtp_am824_set_midi_position(struct amdtp_stream *s,
	unsigned int position)
	{
	struct amdtp_am824 *p = s->protocol;

	p->midi_position = position;
	}
	EXPORT_SYMBOL_GPL(amdtp_am824_set_midi_position);

	static void write_pcm_s32(struct amdtp_stream s, struct snd_pcm_substream pcm,
	__be32 *buffer, unsigned int frames,
	unsigned int pcm_frames)
	{
	struct amdtp_am824 *p = s->protocol;
	unsigned int channels = p->pcm_channels;
	struct snd_pcm_runtime *runtime = pcm->runtime;
	unsigned int pcm_buffer_pointer;
	int remaining_frames;
	const u32 *src;
	int i, c;

	pcm_buffer_pointer = s->pcm_buffer_pointer + pcm_frames;
	pcm_buffer_pointer %= runtime->buffer_size;

	src = (void *)runtime->dma_area +
	frames_to_bytes(runtime, pcm_buffer_pointer);
	remaining_frames = runtime->buffer_size - pcm_buffer_pointer;

	for (i = 0; i < frames; ++i) {
	for (c = 0; c < channels; ++c) {
	buffer[p->pcm_positions[c]] =
	cpu_to_be32((*src >> 8) \| 0x40000000);
	src++;
	}
	buffer += s->data_block_quadlets;
	if (--remaining_frames == 0)
	src = (void *)runtime->dma_area;
	}
	}

	static void read_pcm_s32(struct amdtp_stream s, struct snd_pcm_substream pcm,
	__be32 *buffer, unsigned int frames,
	unsigned int pcm_frames)
	{
	struct amdtp_am824 *p = s->protocol;
	unsigned int channels = p->pcm_channels;
	struct snd_pcm_runtime *runtime = pcm->runtime;
	unsigned int pcm_buffer_pointer;
	int remaining_frames;
	u32 *dst;
	int i, c;

	pcm_buffer_pointer = s->pcm_buffer_pointer + pcm_frames;
	pcm_buffer_pointer %= runtime->buffer_size;

	dst = (void *)runtime->dma_area +
	frames_to_bytes(runtime, pcm_buffer_pointer);
	remaining_frames = runtime->buffer_size - pcm_buffer_pointer;

	for (i = 0; i < frames; ++i) {
	for (c = 0; c < channels; ++c) {
	*dst = be32_to_cpu(buffer[p->pcm_positions[c]]) << 8;
	dst++;
	}
	buffer += s->data_block_quadlets;
	if (--remaining_frames == 0)
	dst = (void *)runtime->dma_area;
	}
	}

	static void write_pcm_silence(struct amdtp_stream *s,
	__be32 *buffer, unsigned int frames)
	{
	struct amdtp_am824 *p = s->protocol;
	unsigned int i, c, channels = p->pcm_channels;

	for (i = 0; i < frames; ++i) {
	for (c = 0; c < channels; ++c)
	buffer[p->pcm_positions[c]] = cpu_to_be32(0x40000000);
	buffer += s->data_block_quadlets;
	}
	}

	/**
	* amdtp_am824_add_pcm_hw_constraints - add hw constraints for PCM substream
	* @s: the AMDTP stream for AM824 data block, must be initialized.
	* @runtime: the PCM substream runtime
	*
	*/
	int amdtp_am824_add_pcm_hw_constraints(struct amdtp_stream *s,
	struct snd_pcm_runtime *runtime)
	{
	int err;

	err = amdtp_stream_add_pcm_hw_constraints(s, runtime);
	if (err < 0)
	return err;

	/* AM824 in IEC 61883-6 can deliver 24bit data. */
	return snd_pcm_hw_constraint_msbits(runtime, 0, 32, 24);
	}
	EXPORT_SYMBOL_GPL(amdtp_am824_add_pcm_hw_constraints);

	/**
	* amdtp_am824_midi_trigger - start/stop playback/capture with a MIDI device
	* @s: the AMDTP stream
	* @port: index of MIDI port
	* @midi: the MIDI device to be started, or %NULL to stop the current device
	*
	* Call this function on a running isochronous stream to enable the actual
	* transmission of MIDI data. This function should be called from the MIDI
	* device's .trigger callback.
	*/
	void amdtp_am824_midi_trigger(struct amdtp_stream *s, unsigned int port,
	struct snd_rawmidi_substream *midi)
	{
	struct amdtp_am824 *p = s->protocol;

	if (port < p->midi_ports)
	WRITE_ONCE(p->midi[port], midi);
	}
	EXPORT_SYMBOL_GPL(amdtp_am824_midi_trigger);

	/*
	* To avoid sending MIDI bytes at too high a rate, assume that the receiving
	* device has a FIFO, and track how much it is filled. This values increases
	* by one whenever we send one byte in a packet, but the FIFO empties at
	* a constant rate independent of our packet rate. One packet has syt_interval
	* samples, so the number of bytes that empty out of the FIFO, per packet(!),
	* is MIDI_BYTES_PER_SECOND * syt_interval / sample_rate. To avoid storing
	* fractional values, the values in midi_fifo_used[] are measured in bytes
	* multiplied by the sample rate.
	*/
	static bool midi_ratelimit_per_packet(struct amdtp_stream *s, unsigned int port)
	{
	struct amdtp_am824 *p = s->protocol;
	int used;

	used = p->midi_fifo_used[port];
	if (used == 0) /* common shortcut */
	return true;

	used -= MIDI_BYTES_PER_SECOND * s->syt_interval;
	used = max(used, 0);
	p->midi_fifo_used[port] = used;

	return used < p->midi_fifo_limit;
	}

	static void midi_rate_use_one_byte(struct amdtp_stream *s, unsigned int port)
	{
	struct amdtp_am824 *p = s->protocol;

	p->midi_fifo_used[port] += amdtp_rate_table[s->sfc];
	}

	static void write_midi_messages(struct amdtp_stream s, __be32 buffer,
	unsigned int frames, unsigned int data_block_counter)
	{
	struct amdtp_am824 *p = s->protocol;
	unsigned int f, port;
	u8 *b;

	for (f = 0; f < frames; f++) {
	b = (u8 *)&buffer[p->midi_position];

	port = (data_block_counter + f) % 8;
	if (f < MAX_MIDI_RX_BLOCKS &&
	midi_ratelimit_per_packet(s, port) &&
	p->midi[port] != NULL &&
	snd_rawmidi_transmit(p->midi[port], &b[1], 1) == 1) {
	midi_rate_use_one_byte(s, port);
	b[0] = 0x81;
	} else {
	b[0] = 0x80;
	b[1] = 0;
	}
	b[2] = 0;
	b[3] = 0;

	buffer += s->data_block_quadlets;
	}
	}

	static void read_midi_messages(struct amdtp_stream s, __be32 buffer,
	unsigned int frames, unsigned int data_block_counter)
	{
	struct amdtp_am824 *p = s->protocol;
	int len;
	u8 *b;
	int f;

	for (f = 0; f < frames; f++) {
	unsigned int port = f;

	if (!(s->flags & CIP_UNALIGHED_DBC))
	port += data_block_counter;
	port %= 8;
	b = (u8 *)&buffer[p->midi_position];

	len = b[0] - 0x80;
	if ((1 <= len) && (len <= 3) && (p->midi[port]))
	snd_rawmidi_receive(p->midi[port], b + 1, len);

	buffer += s->data_block_quadlets;
	}
	}

	static unsigned int process_it_ctx_payloads(struct amdtp_stream *s,
	const struct pkt_desc *descs,
	unsigned int packets,
	struct snd_pcm_substream *pcm)
	{
	struct amdtp_am824 *p = s->protocol;
	unsigned int pcm_frames = 0;
	int i;

	for (i = 0; i < packets; ++i) {
	const struct pkt_desc *desc = descs + i;
	__be32 *buf = desc->ctx_payload;
	unsigned int data_blocks = desc->data_blocks;

	if (pcm) {
	write_pcm_s32(s, pcm, buf, data_blocks, pcm_frames);
	pcm_frames += data_blocks * p->frame_multiplier;
	} else {
	write_pcm_silence(s, buf, data_blocks);
	}

	if (p->midi_ports) {
	write_midi_messages(s, buf, data_blocks,
	desc->data_block_counter);
	}
	}

	return pcm_frames;
	}

	static unsigned int process_ir_ctx_payloads(struct amdtp_stream *s,
	const struct pkt_desc *descs,
	unsigned int packets,
	struct snd_pcm_substream *pcm)
	{
	struct amdtp_am824 *p = s->protocol;
	unsigned int pcm_frames = 0;
	int i;

	for (i = 0; i < packets; ++i) {
	const struct pkt_desc *desc = descs + i;
	__be32 *buf = desc->ctx_payload;
	unsigned int data_blocks = desc->data_blocks;

	if (pcm) {
	read_pcm_s32(s, pcm, buf, data_blocks, pcm_frames);
	pcm_frames += data_blocks * p->frame_multiplier;
	}

	if (p->midi_ports) {
	read_midi_messages(s, buf, data_blocks,
	desc->data_block_counter);
	}
	}

	return pcm_frames;
	}

	/**
	* amdtp_am824_init - initialize an AMDTP stream structure to handle AM824
	* data block
	* @s: the AMDTP stream to initialize
	* @unit: the target of the stream
	* @dir: the direction of stream
	* @flags: the packet transmission method to use
	*/
	int amdtp_am824_init(struct amdtp_stream s, struct fw_unit unit,
	enum amdtp_stream_direction dir, enum cip_flags flags)
	{
	amdtp_stream_process_ctx_payloads_t process_ctx_payloads;

	if (dir == AMDTP_IN_STREAM)
	process_ctx_payloads = process_ir_ctx_payloads;
	else
	process_ctx_payloads = process_it_ctx_payloads;

	return amdtp_stream_init(s, unit, dir, flags, CIP_FMT_AM,
	process_ctx_payloads, sizeof(struct amdtp_am824));
	}
	EXPORT_SYMBOL_GPL(amdtp_am824_init);