When audio and music units have some quirks in their sequence of packet,
it's really hard for non-owners to identify the quirks. Although developers
need dumps for sequence of packets, it's difficult for users who have no
knowledges and no equipments for this purpose.

This commit adds tracepoints for this situation. When users encounter
the issue, they can dump a part of packet data via Linux tracing framework
as long as using drivers in ALSA firewire stack.

Additionally, tracepoints for outgoing packets will be our help to check
and debug packet processing of ALSA firewire stack.

This commit newly adds 'snd_firewire_lib' subsystem with 'in_packet' and
'out_packet' events. In the events, some attributes of packets and the
index of packet managed by this module are recorded per packet.

This is an usage:

$ trace-cmd record -e snd_firewire_lib:out_packet \
                   -e snd_firewire_lib:in_packet
/sys/kernel/tracing/events/snd_firewire_lib/out_packet/filter
/sys/kernel/tracing/events/snd_firewire_lib/in_packet/filter
Hit Ctrl^C to stop recording
^C
$ trace-cmd report trace.dat
...
23647.033934: in_packet:  01 4073 ffc0 ffc1 00 000f0040 9001b2d1 122 44
23647.033936: in_packet:  01 4074 ffc0 ffc1 00 000f0048 9001c83b 122 45
23647.033937: in_packet:  01 4075 ffc0 ffc1 00 000f0050 9001ffff 002 46
23647.033938: in_packet:  01 4076 ffc0 ffc1 00 000f0050 9001e1a6 122 47
23647.035426: out_packet: 01 4123 ffc1 ffc0 01 010f00d0 9001fb40 122 17
23647.035428: out_packet: 01 4124 ffc1 ffc0 01 010f00d8 9001ffff 002 18
23647.035429: out_packet: 01 4125 ffc1 ffc0 01 010f00d8 900114aa 122 19
23647.035430: out_packet: 01 4126 ffc1 ffc0 01 010f00e0 90012a15 122 20
(Here, some common fields are omitted so that a line to be within 80
characters.)
...

One line represent one packet. The legend for the last nine fields is:
 - The second of cycle scheduled for the packet
 - The count of cycle scheduled for the packet
 - The ID of node as source (hex)
  - Some devices transfer packets with invalid source node ID in their CIP
    header.
 - The ID of node as destination (hex)
  - The value is not in CIP header of packets.
 - The value of isochronous channel
 - The first quadlet of CIP header (hex)
 - The second quadlet of CIP header (hex)
 - The number of included quadlets
 - The index of packet in a buffer maintained by this module

This is an example to parse these lines from text file by Python3 script:

\#!/usr/bin/env python3
import sys

def parse_ts(second, cycle, syt):
    offset = syt & 0xfff
    syt >>= 12
    if cycle & 0x0f > syt:
        cycle += 0x10
    cycle &= 0x1ff0
    cycle |= syt
    second += cycle // 8000
    cycle %= 8000
    # In CYCLE_TIMER of 1394 OHCI, second is represented in 8 bit.
    second %= 128
    return (second, cycle, offset)

def calc_ts(second, cycle, offset):
    ts = offset
    ts += cycle * 3072
    # In DMA descriptor of 1394 OHCI, second is represented in 3 bit.
    ts += (second % 8) * 8000 * 3072
    return ts

def subtract_ts(minuend, subtrahend):
    # In DMA descriptor of 1394 OHCI, second is represented in 3 bit.
    if minuend < subtrahend:
        minuend += 8 * 8000 * 3072
    return minuend - subtrahend

if len(sys.argv) != 2:
    print('At least, one argument is required for packet dump.')
    sys.exit()

filename = sys.argv[1]

data = []

prev = 0
with open(filename, 'r') as f:
    for line in f:
        pos = line.find('packet:')
        if pos < 0:
            continue

        pos += len('packet:')
        line = line[pos:].strip()
        fields = line.split(' ')

        datum = []

        datum.append(fields[8])

        syt = int(fields[6][4:], 16)

        # Empty packet in IEC 61883-1, or NODATA in IEC 61883-6
        if syt == 0xffff:
            data_blocks = 0
        else:
            payload_size = int(fields[7], 10)
            data_block_size = int(fields[5][2:4], 16)
            data_blocks = (payload_size - 2) / data_block_size
        datum.append(data_blocks)

        second = int(fields[0], 10)
        cycle = int(fields[1], 10)
        start = (second << 25) | (cycle << 12)
        datum.append('0x{0:08x}'.format(start))
        start = calc_ts(second, cycle, 0)

        datum.append("0x" + fields[5])
        datum.append("0x" + fields[6])

        if syt == 0xffff:
            second = 0
            cycle = 0
            tick = 0
        else:
            second, cycle, tick = parse_ts(second, cycle, syt)
        ts = calc_ts(second, cycle, tick)
        datum.append(start)
        datum.append(ts)
        if ts == 0:
            datum.append(0)
            datum.append(0)
        else:
            # Usual case, or a case over 8 seconds.
            if ts > start or start > 7 * 8000 * 3072:
                datum.append(subtract_ts(ts, start))
                if ts > prev or start > 7 * 8000 * 3072:
                    gap = subtract_ts(ts, prev)
                    datum.append(gap)
                else:
                    datum.append('backward')
            else:
                datum.append('invalid')
            prev = ts

        data.append(datum)

sys.exit()

The data variable includes array with these elements:
- The index of the packet
- The number of data blocks in the packet
- The value of cycle count (hex)
- The value of CIP header 1 (hex)
- The value of CIP header 2 (hex)
- The value of cycle count (tick)
- The value of calculated presentation timestamp (tick)
- The offset between the cycle count and presentation timestamp
- The elapsed ticks from the previous presentation timestamp

Signed-off-by: Takashi Sakamoto <o-takashi@sakamocchi.jp>
Signed-off-by: Takashi Iwai <tiwai@suse.de>