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ALSA: firewire-lib/fireworks: fix miss detection of received MIDI mes…
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…sages

In IEC 61883-6, 8 MIDI data streams are multiplexed into single
MIDI conformant data channel. The index of stream is calculated by
modulo 8 of the value of data block counter.

In fireworks, the value of data block counter in CIP header has a quirk
with firmware version v5.0.0, v5.7.3 and v5.8.0. This brings ALSA
IEC 61883-1/6 packet streaming engine to miss detection of MIDI
messages.

This commit fixes the miss detection to modify the value of data block
counter for the modulo calculation.

For maintainers, this bug exists since a commit 18f5ed3 ("ALSA:
fireworks/firewire-lib: add support for recent firmware quirk") in Linux
kernel v4.2. There're many changes since the commit.  This fix can be
backported to Linux kernel v4.4 or later. I tagged a base commit to the
backport for your convenience.

Besides, my work for Linux kernel v5.3 brings heavy code refactoring and
some structure members are renamed in 'sound/firewire/amdtp-stream.h'.
The content of this patch brings conflict when merging -rc tree with
this patch and the latest tree. I request maintainers to solve the
conflict to replace 'tx_first_dbc' with 'ctx_data.tx.first_dbc'.

Fixes: df075fe ("ALSA: firewire-lib: complete AM824 data block processing layer")
Cc: <[email protected]> # v4.4+
Signed-off-by: Takashi Sakamoto <[email protected]>
Signed-off-by: Takashi Iwai <[email protected]>
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takaswie authored and tiwai committed Jul 1, 2019
1 parent c3ea60c commit 7fbd175
Showing 1 changed file with 1 addition and 1 deletion.
2 changes: 1 addition & 1 deletion sound/firewire/amdtp-am824.c
Original file line number Diff line number Diff line change
Expand Up @@ -321,7 +321,7 @@ static void read_midi_messages(struct amdtp_stream *s,
u8 *b;

for (f = 0; f < frames; f++) {
port = (s->data_block_counter + f) % 8;
port = (8 - s->tx_first_dbc + s->data_block_counter + f) % 8;
b = (u8 *)&buffer[p->midi_position];

len = b[0] - 0x80;
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