Fireworks uses TSB43CB43(IceLynx-Micro) as its IEC 61883-1/6 interface.
This chip includes ARM7 core, and loads and runs program. The firmware
is stored in on-board memory and loaded every powering-on from it.

Echo Audio ships several versions of firmwares for each model. These
firmwares have each quirk and the quirk changes a sequence of packets.

As long as I investigated, AudioFire2/AudioFire4/AudioFirePre8 have a
quirk to transfer a first packet with 0x02 in its dbc field. This causes
ALSA Fireworks driver to detect discontinuity. In this case, firmware
version 5.7.0, 5.7.3 and 5.8.0 are used.

Payload  CIP      CIP
quadlets header1  header2
02       00050002 90ffffff <-
42       0005000a 90013000
42       00050012 90014400
42       0005001a 90015800
02       0005001a 90ffffff
42       00050022 90019000
42       0005002a 9001a400
42       00050032 9001b800
02       00050032 90ffffff
42       0005003a 9001d000
42       00050042 9001e400
42       0005004a 9001f800
02       0005004a 90ffffff
(AudioFire2 with firmware version 5.7.)

$ dmesg
snd-fireworks fw1.0: Detect discontinuity of CIP: 00 02

These models, AudioFire8 (since Jul 2009 ) and Gibson Robot Interface
Pack series uses the same ARM binary as their firmware. Thus, this
quirk may be observed among them.

This commit adds a new member for AMDTP structure. This member represents
the value of dbc field in a first AMDTP packet. Drivers can set it with
a preferred value according to model's quirk.

Tested-by: Johannes Oertei <johannes.oertel@uni-due.de>
Signed-off-by: Takashi Sakamoto <o-takashi@sakamocchi.jp>
Cc: <stable@vger.kernel.org>
Signed-off-by: Takashi Iwai <tiwai@suse.de>