Linux Audio

Check our new training course

Embedded Linux Audio

Check our new training course
with Creative Commons CC-BY-SA
lecture materials

Bootlin logo

Elixir Cross Referencer

Loading...
  1
  2
  3
  4
  5
  6
  7
  8
  9
 10
 11
 12
 13
 14
 15
 16
 17
 18
 19
 20
 21
 22
 23
 24
 25
 26
 27
 28
 29
 30
 31
 32
 33
 34
 35
 36
 37
 38
 39
 40
 41
 42
 43
 44
 45
 46
 47
 48
 49
 50
 51
 52
 53
 54
 55
 56
 57
 58
 59
 60
 61
 62
 63
 64
 65
 66
 67
 68
 69
 70
 71
 72
 73
 74
 75
 76
 77
 78
 79
 80
 81
 82
 83
 84
 85
 86
 87
 88
 89
 90
 91
 92
 93
 94
 95
 96
 97
 98
 99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
/*
 * 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\n", 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\n");
		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);