/*
 * 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 <sound/pcm_params.h>
#include "amdtp-stream.h"

#define TICKS_PER_CYCLE         3072
#define CYCLES_PER_SECOND       8000
#define TICKS_PER_SECOND        (TICKS_PER_CYCLE * CYCLES_PER_SECOND)

/* Always support Linux tracing subsystem. */
#define CREATE_TRACE_POINTS
#include "amdtp-stream-trace.h"

#define TRANSFER_DELAY_TICKS    0x2e00 /* 479.17 microseconds */

/* isochronous header parameters */
#define ISO_DATA_LENGTH_SHIFT   16
#define TAG_NO_CIP_HEADER       0
#define TAG_CIP                 1

/* common isochronous packet header parameters */
#define CIP_EOH_SHIFT           31
#define CIP_EOH                 (1u << CIP_EOH_SHIFT)
#define CIP_EOH_MASK            0x80000000
#define CIP_SID_SHIFT           24
#define CIP_SID_MASK            0x3f000000
#define CIP_DBS_MASK            0x00ff0000
#define CIP_DBS_SHIFT           16
#define CIP_SPH_MASK            0x00000400
#define CIP_SPH_SHIFT           10
#define CIP_DBC_MASK            0x000000ff
#define CIP_FMT_SHIFT           24
#define CIP_FMT_MASK            0x3f000000
#define CIP_FDF_MASK            0x00ff0000
#define CIP_FDF_SHIFT           16
#define CIP_SYT_MASK            0x0000ffff
#define CIP_SYT_NO_INFO         0xffff

/* Audio and Music transfer protocol specific parameters */
#define CIP_FMT_AM              0x10
#define AMDTP_FDF_NO_DATA       0xff

/* TODO: make these configurable */
#define INTERRUPT_INTERVAL      16
#define QUEUE_LENGTH            48

#define IN_PACKET_HEADER_SIZE   4
#define OUT_PACKET_HEADER_SIZE  0

static void pcm_period_tasklet(unsigned long data);

/**
 * amdtp_stream_init - initialize an AMDTP stream structure
 * @s: the AMDTP stream to initialize
 * @unit: the target of the stream
 * @dir: the direction of stream
 * @flags: the packet transmission method to use
 * @fmt: the value of fmt field in CIP header
 * @process_data_blocks: callback handler to process data blocks
 * @protocol_size: the size to allocate newly for protocol
 */
int amdtp_stream_init(struct amdtp_stream *s, struct fw_unit *unit,
                      enum amdtp_stream_direction dir, enum cip_flags flags,
                      unsigned int fmt,
                      amdtp_stream_process_data_blocks_t process_data_blocks,
                      unsigned int protocol_size)
{
        if (process_data_blocks == NULL)
                return -EINVAL;

        s->protocol = kzalloc(protocol_size, GFP_KERNEL);
        if (!s->protocol)
                return -ENOMEM;

        s->unit = unit;
        s->direction = dir;
        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;

        init_waitqueue_head(&s->callback_wait);
        s->callbacked = false;

        s->fmt = fmt;
        s->process_data_blocks = process_data_blocks;

        return 0;
}
EXPORT_SYMBOL(amdtp_stream_init);

/**
 * amdtp_stream_destroy - free stream resources
 * @s: the AMDTP stream to destroy
 */
void amdtp_stream_destroy(struct amdtp_stream *s)
{
        /* Not initialized. */
        if (s->protocol == NULL)
                return;

        WARN_ON(amdtp_stream_running(s));
        kfree(s->protocol);
        mutex_destroy(&s->mutex);
}
EXPORT_SYMBOL(amdtp_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);

const unsigned int amdtp_rate_table[CIP_SFC_COUNT] = {
        [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,
};
EXPORT_SYMBOL(amdtp_rate_table);

/**
 * amdtp_stream_add_pcm_hw_constraints - add hw constraints for PCM substream
 * @s:          the AMDTP stream, which must be initialized.
 * @runtime:    the PCM substream runtime
 */
int amdtp_stream_add_pcm_hw_constraints(struct amdtp_stream *s,
                                        struct snd_pcm_runtime *runtime)
{
        struct snd_pcm_hardware *hw = &runtime->hw;
        int err;

        hw->info = SNDRV_PCM_INFO_BATCH |
                   SNDRV_PCM_INFO_BLOCK_TRANSFER |
                   SNDRV_PCM_INFO_INTERLEAVED |
                   SNDRV_PCM_INFO_JOINT_DUPLEX |
                   SNDRV_PCM_INFO_MMAP |
                   SNDRV_PCM_INFO_MMAP_VALID;

        /* SNDRV_PCM_INFO_BATCH */
        hw->periods_min = 2;
        hw->periods_max = UINT_MAX;

        /* bytes for a frame */
        hw->period_bytes_min = 4 * hw->channels_max;

        /* Just to prevent from allocating much pages. */
        hw->period_bytes_max = hw->period_bytes_min * 2048;
        hw->buffer_bytes_max = hw->period_bytes_max * hw->periods_min;

        /*
         * Currently firewire-lib processes 16 packets in one software
         * interrupt callback. This equals to 2msec but actually the
         * interval of the interrupts has a jitter.
         * Additionally, even if adding a constraint to fit period size to
         * 2msec, actual calculated frames per period doesn't equal to 2msec,
         * depending on sampling rate.
         * Anyway, the interval to call snd_pcm_period_elapsed() cannot 2msec.
         * Here let us use 5msec for safe period interrupt.
         */
        err = snd_pcm_hw_constraint_minmax(runtime,
                                           SNDRV_PCM_HW_PARAM_PERIOD_TIME,
                                           5000, UINT_MAX);
        if (err < 0)
                goto end;

        /* Non-Blocking stream has no more constraints */
        if (!(s->flags & CIP_BLOCKING))
                goto end;

        /*
         * One AMDTP packet can include some frames. In blocking mode, the
         * number equals to SYT_INTERVAL. So the number is 8, 16 or 32,
         * depending on its sampling rate. For accurate period interrupt, it's
         * preferrable to align period/buffer sizes to current SYT_INTERVAL.
         *
         * TODO: These constraints can be improved with proper rules.
         * Currently apply LCM of SYT_INTERVALs.
         */
        err = snd_pcm_hw_constraint_step(runtime, 0,
                                         SNDRV_PCM_HW_PARAM_PERIOD_SIZE, 32);
        if (err < 0)
                goto end;
        err = snd_pcm_hw_constraint_step(runtime, 0,
                                         SNDRV_PCM_HW_PARAM_BUFFER_SIZE, 32);
end:
        return err;
}
EXPORT_SYMBOL(amdtp_stream_add_pcm_hw_constraints);

/**
 * amdtp_stream_set_parameters - set stream parameters
 * @s: the AMDTP stream to configure
 * @rate: the sample rate
 * @data_block_quadlets: the size of a data block in quadlet unit
 *
 * The parameters must be set before the stream is started, and must not be
 * changed while the stream is running.
 */
int amdtp_stream_set_parameters(struct amdtp_stream *s, unsigned int rate,
                                unsigned int data_block_quadlets)
{
        unsigned int sfc;

        for (sfc = 0; sfc < ARRAY_SIZE(amdtp_rate_table); ++sfc) {
                if (amdtp_rate_table[sfc] == rate)
                        break;
        }
        if (sfc == ARRAY_SIZE(amdtp_rate_table))
                return -EINVAL;

        s->sfc = sfc;
        s->data_block_quadlets = data_block_quadlets;
        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;

        return 0;
}
EXPORT_SYMBOL(amdtp_stream_set_parameters);

/**
 * amdtp_stream_get_max_payload - get the stream's packet size
 * @s: the AMDTP stream
 *
 * This function must not be called before the stream has been configured
 * with amdtp_stream_set_parameters().
 */
unsigned int amdtp_stream_get_max_payload(struct amdtp_stream *s)
{
        unsigned int multiplier = 1;
        unsigned int header_size = 0;

        if (s->flags & CIP_JUMBO_PAYLOAD)
                multiplier = 5;
        if (!(s->flags & CIP_NO_HEADER))
                header_size = 8;

        return header_size +
                s->syt_interval * s->data_block_quadlets * 4 * multiplier;
}
EXPORT_SYMBOL(amdtp_stream_get_max_payload);

/**
 * amdtp_stream_pcm_prepare - prepare PCM device for running
 * @s: the AMDTP stream
 *
 * This function should be called from the PCM device's .prepare callback.
 */
void amdtp_stream_pcm_prepare(struct amdtp_stream *s)
{
        tasklet_kill(&s->period_tasklet);
        s->pcm_buffer_pointer = 0;
        s->pcm_period_pointer = 0;
}
EXPORT_SYMBOL(amdtp_stream_pcm_prepare);

static unsigned int calculate_data_blocks(struct amdtp_stream *s,
                                          unsigned int syt)
{
        unsigned int phase, data_blocks;

        /* Blocking mode. */
        if (s->flags & CIP_BLOCKING) {
                /* This module generate empty packet for 'no data'. */
                if (syt == CIP_SYT_NO_INFO)
                        data_blocks = 0;
                else
                        data_blocks = s->syt_interval;
        /* Non-blocking mode. */
        } else {
                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_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 & CIP_SYT_MASK;
        } else {
                return CIP_SYT_NO_INFO;
        }
}

static void update_pcm_pointers(struct amdtp_stream *s,
                                struct snd_pcm_substream *pcm,
                                unsigned int frames)
{
        unsigned int ptr;

        ptr = s->pcm_buffer_pointer + frames;
        if (ptr >= pcm->runtime->buffer_size)
                ptr -= pcm->runtime->buffer_size;
        ACCESS_ONCE(s->pcm_buffer_pointer) = ptr;

        s->pcm_period_pointer += frames;
        if (s->pcm_period_pointer >= pcm->runtime->period_size) {
                s->pcm_period_pointer -= pcm->runtime->period_size;
                tasklet_hi_schedule(&s->period_tasklet);
        }
}

static void pcm_period_tasklet(unsigned long data)
{
        struct amdtp_stream *s = (void *)data;
        struct snd_pcm_substream *pcm = ACCESS_ONCE(s->pcm);

        if (pcm)
                snd_pcm_period_elapsed(pcm);
}

static int queue_packet(struct amdtp_stream *s, unsigned int header_length,
                        unsigned int payload_length)
{
        struct fw_iso_packet p = {0};
        int err = 0;

        if (IS_ERR(s->context))
                goto end;

        p.interrupt = IS_ALIGNED(s->packet_index + 1, INTERRUPT_INTERVAL);
        p.tag = s->tag;
        p.header_length = header_length;
        if (payload_length > 0)
                p.payload_length = payload_length;
        else
                p.skip = true;
        err = fw_iso_context_queue(s->context, &p, &s->buffer.iso_buffer,
                                   s->buffer.packets[s->packet_index].offset);
        if (err < 0) {
                dev_err(&s->unit->device, "queueing error: %d\n", err);
                goto end;
        }

        if (++s->packet_index >= QUEUE_LENGTH)
                s->packet_index = 0;
end:
        return err;
}

static inline int queue_out_packet(struct amdtp_stream *s,
                                   unsigned int payload_length)
{
        return queue_packet(s, OUT_PACKET_HEADER_SIZE, payload_length);
}

static inline int queue_in_packet(struct amdtp_stream *s)
{
        return queue_packet(s, IN_PACKET_HEADER_SIZE, s->max_payload_length);
}

static int handle_out_packet(struct amdtp_stream *s,
                             unsigned int payload_length, unsigned int cycle,
                             unsigned int index)
{
        __be32 *buffer;
        unsigned int syt;
        unsigned int data_blocks;
        unsigned int pcm_frames;
        struct snd_pcm_substream *pcm;

        buffer = s->buffer.packets[s->packet_index].buffer;
        syt = calculate_syt(s, cycle);
        data_blocks = calculate_data_blocks(s, syt);
        pcm_frames = s->process_data_blocks(s, buffer + 2, data_blocks, &syt);

        if (s->flags & CIP_DBC_IS_END_EVENT)
                s->data_block_counter =
                                (s->data_block_counter + data_blocks) & 0xff;

        buffer[0] = cpu_to_be32(ACCESS_ONCE(s->source_node_id_field) |
                                (s->data_block_quadlets << CIP_DBS_SHIFT) |
                                ((s->sph << CIP_SPH_SHIFT) & CIP_SPH_MASK) |
                                s->data_block_counter);
        buffer[1] = cpu_to_be32(CIP_EOH |
                                ((s->fmt << CIP_FMT_SHIFT) & CIP_FMT_MASK) |
                                ((s->fdf << CIP_FDF_SHIFT) & CIP_FDF_MASK) |
                                (syt & CIP_SYT_MASK));

        if (!(s->flags & CIP_DBC_IS_END_EVENT))
                s->data_block_counter =
                                (s->data_block_counter + data_blocks) & 0xff;
        payload_length = 8 + data_blocks * 4 * s->data_block_quadlets;

        trace_out_packet(s, cycle, buffer, payload_length, index);

        if (queue_out_packet(s, payload_length) < 0)
                return -EIO;

        pcm = ACCESS_ONCE(s->pcm);
        if (pcm && pcm_frames > 0)
                update_pcm_pointers(s, pcm, pcm_frames);

        /* No need to return the number of handled data blocks. */
        return 0;
}

static int handle_out_packet_without_header(struct amdtp_stream *s,
                        unsigned int payload_length, unsigned int cycle,
                        unsigned int index)
{
        __be32 *buffer;
        unsigned int syt;
        unsigned int data_blocks;
        unsigned int pcm_frames;
        struct snd_pcm_substream *pcm;

        buffer = s->buffer.packets[s->packet_index].buffer;
        syt = calculate_syt(s, cycle);
        data_blocks = calculate_data_blocks(s, syt);
        pcm_frames = s->process_data_blocks(s, buffer, data_blocks, &syt);
        s->data_block_counter = (s->data_block_counter + data_blocks) & 0xff;

        payload_length = data_blocks * 4 * s->data_block_quadlets;

        trace_out_packet_without_header(s, cycle, payload_length, data_blocks,
                                        index);

        if (queue_out_packet(s, payload_length) < 0)
                return -EIO;

        pcm = ACCESS_ONCE(s->pcm);
        if (pcm && pcm_frames > 0)
                update_pcm_pointers(s, pcm, pcm_frames);

        /* No need to return the number of handled data blocks. */
        return 0;
}

static int handle_in_packet(struct amdtp_stream *s,
                            unsigned int payload_length, unsigned int cycle,
                            unsigned int index)
{
        __be32 *buffer;
        u32 cip_header[2];
        unsigned int sph, fmt, fdf, syt;
        unsigned int data_block_quadlets, data_block_counter, dbc_interval;
        unsigned int data_blocks;
        struct snd_pcm_substream *pcm;
        unsigned int pcm_frames;
        bool lost;

        buffer = s->buffer.packets[s->packet_index].buffer;
        cip_header[0] = be32_to_cpu(buffer[0]);
        cip_header[1] = be32_to_cpu(buffer[1]);

        trace_in_packet(s, cycle, cip_header, payload_length, index);

        /*
         * This module supports 'Two-quadlet CIP header with SYT field'.
         * For convenience, also check FMT field is AM824 or not.
         */
        if ((((cip_header[0] & CIP_EOH_MASK) == CIP_EOH) ||
             ((cip_header[1] & CIP_EOH_MASK) != CIP_EOH)) &&
            (!(s->flags & CIP_HEADER_WITHOUT_EOH))) {
                dev_info_ratelimited(&s->unit->device,
                                "Invalid CIP header for AMDTP: %08X:%08X\n",
                                cip_header[0], cip_header[1]);
                data_blocks = 0;
                pcm_frames = 0;
                goto end;
        }

        /* Check valid protocol or not. */
        sph = (cip_header[0] & CIP_SPH_MASK) >> CIP_SPH_SHIFT;
        fmt = (cip_header[1] & CIP_FMT_MASK) >> CIP_FMT_SHIFT;
        if (sph != s->sph || fmt != s->fmt) {
                dev_info_ratelimited(&s->unit->device,
                                     "Detect unexpected protocol: %08x %08x\n",
                                     cip_header[0], cip_header[1]);
                data_blocks = 0;
                pcm_frames = 0;
                goto end;
        }

        /* Calculate data blocks */
        fdf = (cip_header[1] & CIP_FDF_MASK) >> CIP_FDF_SHIFT;
        if (payload_length < 12 ||
            (fmt == CIP_FMT_AM && fdf == AMDTP_FDF_NO_DATA)) {
                data_blocks = 0;
        } else {
                data_block_quadlets =
                        (cip_header[0] & CIP_DBS_MASK) >> CIP_DBS_SHIFT;
                /* avoid division by zero */
                if (data_block_quadlets == 0) {
                        dev_err(&s->unit->device,
                                "Detect invalid value in dbs field: %08X\n",
                                cip_header[0]);
                        return -EPROTO;
                }
                if (s->flags & CIP_WRONG_DBS)
                        data_block_quadlets = s->data_block_quadlets;

                data_blocks = (payload_length / 4 - 2) /
                                                        data_block_quadlets;
        }

        /* Check data block counter continuity */
        data_block_counter = cip_header[0] & CIP_DBC_MASK;
        if (data_blocks == 0 && (s->flags & CIP_EMPTY_HAS_WRONG_DBC) &&
            s->data_block_counter != UINT_MAX)
                data_block_counter = s->data_block_counter;

        if (((s->flags & CIP_SKIP_DBC_ZERO_CHECK) &&
             data_block_counter == s->tx_first_dbc) ||
            s->data_block_counter == UINT_MAX) {
                lost = false;
        } else if (!(s->flags & CIP_DBC_IS_END_EVENT)) {
                lost = data_block_counter != s->data_block_counter;
        } else {
                if (data_blocks > 0 && s->tx_dbc_interval > 0)
                        dbc_interval = s->tx_dbc_interval;
                else
                        dbc_interval = data_blocks;

                lost = data_block_counter !=
                       ((s->data_block_counter + dbc_interval) & 0xff);
        }

        if (lost) {
                dev_err(&s->unit->device,
                        "Detect discontinuity of CIP: %02X %02X\n",
                        s->data_block_counter, data_block_counter);
                return -EIO;
        }

        syt = be32_to_cpu(buffer[1]) & CIP_SYT_MASK;
        pcm_frames = s->process_data_blocks(s, buffer + 2, data_blocks, &syt);

        if (s->flags & CIP_DBC_IS_END_EVENT)
                s->data_block_counter = data_block_counter;
        else
                s->data_block_counter =
                                (data_block_counter + data_blocks) & 0xff;
end:
        if (queue_in_packet(s) < 0)
                return -EIO;

        pcm = ACCESS_ONCE(s->pcm);
        if (pcm && pcm_frames > 0)
                update_pcm_pointers(s, pcm, pcm_frames);

        return 0;
}

static int handle_in_packet_without_header(struct amdtp_stream *s,
                        unsigned int payload_quadlets, unsigned int cycle,
                        unsigned int index)
{
        __be32 *buffer;
        unsigned int data_blocks;
        struct snd_pcm_substream *pcm;
        unsigned int pcm_frames;

        buffer = s->buffer.packets[s->packet_index].buffer;
        data_blocks = payload_quadlets / s->data_block_quadlets;

        trace_in_packet_without_header(s, cycle, payload_quadlets, data_blocks,
                                       index);

        pcm_frames = s->process_data_blocks(s, buffer, data_blocks, NULL);
        s->data_block_counter = (s->data_block_counter + data_blocks) & 0xff;

        if (queue_in_packet(s) < 0)
                return -EIO;

        pcm = ACCESS_ONCE(s->pcm);
        if (pcm && pcm_frames > 0)
                update_pcm_pointers(s, pcm, pcm_frames);

        return 0;
}

/*
 * In CYCLE_TIMER register of IEEE 1394, 7 bits are used to represent second. On
 * the other hand, in DMA descriptors of 1394 OHCI, 3 bits are used to represent
 * it. Thus, via Linux firewire subsystem, we can get the 3 bits for second.
 */
static inline u32 compute_cycle_count(u32 tstamp)
{
        return (((tstamp >> 13) & 0x07) * 8000) + (tstamp & 0x1fff);
}

static inline u32 increment_cycle_count(u32 cycle, unsigned int addend)
{
        cycle += addend;
        if (cycle >= 8 * CYCLES_PER_SECOND)
                cycle -= 8 * CYCLES_PER_SECOND;
        return cycle;
}

static inline u32 decrement_cycle_count(u32 cycle, unsigned int subtrahend)
{
        if (cycle < subtrahend)
                cycle += 8 * CYCLES_PER_SECOND;
        return cycle - subtrahend;
}

static void out_stream_callback(struct fw_iso_context *context, u32 tstamp,
                                size_t header_length, void *header,
                                void *private_data)
{
        struct amdtp_stream *s = private_data;
        unsigned int i, packets = header_length / 4;
        u32 cycle;

        if (s->packet_index < 0)
                return;

        cycle = compute_cycle_count(tstamp);

        /* Align to actual cycle count for the last packet. */
        cycle = increment_cycle_count(cycle, QUEUE_LENGTH - packets);

        for (i = 0; i < packets; ++i) {
                cycle = increment_cycle_count(cycle, 1);
                if (s->handle_packet(s, 0, cycle, i) < 0) {
                        s->packet_index = -1;
                        if (in_interrupt())
                                amdtp_stream_pcm_abort(s);
                        WRITE_ONCE(s->pcm_buffer_pointer, SNDRV_PCM_POS_XRUN);
                        return;
                }
        }

        fw_iso_context_queue_flush(s->context);
}

static void in_stream_callback(struct fw_iso_context *context, u32 tstamp,
                               size_t header_length, void *header,
                               void *private_data)
{
        struct amdtp_stream *s = private_data;
        unsigned int i, packets;
        unsigned int payload_length, max_payload_length;
        __be32 *headers = header;
        u32 cycle;

        if (s->packet_index < 0)
                return;

        /* The number of packets in buffer */
        packets = header_length / IN_PACKET_HEADER_SIZE;

        cycle = compute_cycle_count(tstamp);

        /* Align to actual cycle count for the last packet. */
        cycle = decrement_cycle_count(cycle, packets);

        /* For buffer-over-run prevention. */
        max_payload_length = s->max_payload_length;

        for (i = 0; i < packets; i++) {
                cycle = increment_cycle_count(cycle, 1);

                /* The number of bytes in this packet */
                payload_length =
                        (be32_to_cpu(headers[i]) >> ISO_DATA_LENGTH_SHIFT);
                if (payload_length > max_payload_length) {
                        dev_err(&s->unit->device,
                                "Detect jumbo payload: %04x %04x\n",
                                payload_length, max_payload_length);
                        break;
                }

                if (s->handle_packet(s, payload_length, cycle, i) < 0)
                        break;
        }

        /* Queueing error or detecting invalid payload. */
        if (i < packets) {
                s->packet_index = -1;
                if (in_interrupt())
                        amdtp_stream_pcm_abort(s);
                WRITE_ONCE(s->pcm_buffer_pointer, SNDRV_PCM_POS_XRUN);
                return;
        }

        fw_iso_context_queue_flush(s->context);
}

/* this is executed one time */
static void amdtp_stream_first_callback(struct fw_iso_context *context,
                                        u32 tstamp, size_t header_length,
                                        void *header, void *private_data)
{
        struct amdtp_stream *s = private_data;
        u32 cycle;
        unsigned int packets;

        s->max_payload_length = amdtp_stream_get_max_payload(s);

        /*
         * For in-stream, first packet has come.
         * For out-stream, prepared to transmit first packet
         */
        s->callbacked = true;
        wake_up(&s->callback_wait);

        cycle = compute_cycle_count(tstamp);

        if (s->direction == AMDTP_IN_STREAM) {
                packets = header_length / IN_PACKET_HEADER_SIZE;
                cycle = decrement_cycle_count(cycle, packets);
                context->callback.sc = in_stream_callback;
                if (s->flags & CIP_NO_HEADER)
                        s->handle_packet = handle_in_packet_without_header;
                else
                        s->handle_packet = handle_in_packet;
        } else {
                packets = header_length / 4;
                cycle = increment_cycle_count(cycle, QUEUE_LENGTH - packets);
                context->callback.sc = out_stream_callback;
                if (s->flags & CIP_NO_HEADER)
                        s->handle_packet = handle_out_packet_without_header;
                else
                        s->handle_packet = handle_out_packet;
        }

        s->start_cycle = cycle;

        context->callback.sc(context, tstamp, header_length, header, s);
}

/**
 * amdtp_stream_start - start transferring packets
 * @s: the AMDTP 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_stream_set_parameters() and it must be started before any PCM or MIDI
 * device can be started.
 */
int amdtp_stream_start(struct amdtp_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 },
        };
        unsigned int header_size;
        enum dma_data_direction dir;
        int type, tag, err;

        mutex_lock(&s->mutex);

        if (WARN_ON(amdtp_stream_running(s) ||
                    (s->data_block_quadlets < 1))) {
                err = -EBADFD;
                goto err_unlock;
        }

        if (s->direction == AMDTP_IN_STREAM)
                s->data_block_counter = UINT_MAX;
        else
                s->data_block_counter = 0;
        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;

        /* initialize packet buffer */
        if (s->direction == AMDTP_IN_STREAM) {
                dir = DMA_FROM_DEVICE;
                type = FW_ISO_CONTEXT_RECEIVE;
                header_size = IN_PACKET_HEADER_SIZE;
        } else {
                dir = DMA_TO_DEVICE;
                type = FW_ISO_CONTEXT_TRANSMIT;
                header_size = OUT_PACKET_HEADER_SIZE;
        }
        err = iso_packets_buffer_init(&s->buffer, s->unit, QUEUE_LENGTH,
                                      amdtp_stream_get_max_payload(s), dir);
        if (err < 0)
                goto err_unlock;

        s->context = fw_iso_context_create(fw_parent_device(s->unit)->card,
                                           type, channel, speed, header_size,
                                           amdtp_stream_first_callback, s);
        if (IS_ERR(s->context)) {
                err = PTR_ERR(s->context);
                if (err == -EBUSY)
                        dev_err(&s->unit->device,
                                "no free stream on this controller\n");
                goto err_buffer;
        }

        amdtp_stream_update(s);

        if (s->flags & CIP_NO_HEADER)
                s->tag = TAG_NO_CIP_HEADER;
        else
                s->tag = TAG_CIP;

        s->packet_index = 0;
        do {
                if (s->direction == AMDTP_IN_STREAM)
                        err = queue_in_packet(s);
                else
                        err = queue_out_packet(s, 0);
                if (err < 0)
                        goto err_context;
        } while (s->packet_index > 0);

        /* NOTE: TAG1 matches CIP. This just affects in stream. */
        tag = FW_ISO_CONTEXT_MATCH_TAG1;
        if ((s->flags & CIP_EMPTY_WITH_TAG0) || (s->flags & CIP_NO_HEADER))
                tag |= FW_ISO_CONTEXT_MATCH_TAG0;

        s->callbacked = false;
        err = fw_iso_context_start(s->context, -1, 0, tag);
        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_stream_start);

/**
 * amdtp_stream_pcm_pointer - get the PCM buffer position
 * @s: the AMDTP stream that transports the PCM data
 *
 * Returns the current buffer position, in frames.
 */
unsigned long amdtp_stream_pcm_pointer(struct amdtp_stream *s)
{
        /*
         * This function is called in software IRQ context of period_tasklet or
         * process context.
         *
         * When the software IRQ context was scheduled by software IRQ context
         * of IR/IT contexts, queued packets were already handled. Therefore,
         * no need to flush the queue in buffer anymore.
         *
         * When the process context reach here, some packets will be already
         * queued in the buffer. These packets should be handled immediately
         * to keep better granularity of PCM pointer.
         *
         * Later, the process context will sometimes schedules software IRQ
         * context of the period_tasklet. Then, no need to flush the queue by
         * the same reason as described for IR/IT contexts.
         */
        if (!in_interrupt() && amdtp_stream_running(s))
                fw_iso_context_flush_completions(s->context);

        return ACCESS_ONCE(s->pcm_buffer_pointer);
}
EXPORT_SYMBOL(amdtp_stream_pcm_pointer);

/**
 * amdtp_stream_pcm_ack - acknowledge queued PCM frames
 * @s: the AMDTP stream that transfers the PCM frames
 *
 * Returns zero always.
 */
int amdtp_stream_pcm_ack(struct amdtp_stream *s)
{
        /*
         * Process isochronous packets for recent isochronous cycle to handle
         * queued PCM frames.
         */
        if (amdtp_stream_running(s))
                fw_iso_context_flush_completions(s->context);

        return 0;
}
EXPORT_SYMBOL(amdtp_stream_pcm_ack);

/**
 * amdtp_stream_update - update the stream after a bus reset
 * @s: the AMDTP stream
 */
void amdtp_stream_update(struct amdtp_stream *s)
{
        /* Precomputing. */
        ACCESS_ONCE(s->source_node_id_field) =
                (fw_parent_device(s->unit)->card->node_id << CIP_SID_SHIFT) &
                                                                CIP_SID_MASK;
}
EXPORT_SYMBOL(amdtp_stream_update);

/**
 * amdtp_stream_stop - stop sending packets
 * @s: the AMDTP stream to stop
 *
 * All PCM and MIDI devices of the stream must be stopped before the stream
 * itself can be stopped.
 */
void amdtp_stream_stop(struct amdtp_stream *s)
{
        mutex_lock(&s->mutex);

        if (!amdtp_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);

        s->callbacked = false;

        mutex_unlock(&s->mutex);
}
EXPORT_SYMBOL(amdtp_stream_stop);

/**
 * amdtp_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_stream_pcm_abort(struct amdtp_stream *s)
{
        struct snd_pcm_substream *pcm;

        pcm = ACCESS_ONCE(s->pcm);
        if (pcm)
                snd_pcm_stop_xrun(pcm);
}
EXPORT_SYMBOL(amdtp_stream_pcm_abort);