[alsa-devel] [PATCH 46/49] bebob/firewire-lib: Add a quirk of wrong dbc in empty packet for M-Audio special Firewire series

[Takashi Sakamoto]

M-Audio Firewire 1814 has a quirk, ProjectMix I/O also has. They transmit
empty packet with wrong value of dbc incremented by 8 at high sampling rate.
According to IEC 61883-1, this value should be the same as the one in
previous packet.

This commit adds a flag named as CIP_EMPTY_HAS_WRONG_DBC. With flag, the value
of dbc in empty packet is overwittern by an expected value.

This is an example of this quirk:
CIP Header 0	CIP Header 1	Payload size
010D0000	9004F759	210
010D0010	90040B59	210
010D0020	90042359	210
01020028	9004FFFF	2  <-
010D0030	90043759	210
010D0040	90044B59	210
010D0050	90046359	210
01020058	9004FFFF	2  <-
010D0060	90047759	210
010D0070	90048B59	210
010D0080	9004A359	210
01020088	9004FFFF	2  <-
010D0090	9004B759	210
010D00A0	9004CB59	210
010D00B0	9004E359	210
010200B8	9004FFFF	2  <-
010D00C0	9004F759	210
010D00D0	90040B59	210
010D00E0	90042359	210

Signed-off-by: Takashi Sakamoto <o-takashi at sakamocchi.jp>
---
 sound/firewire/amdtp.c              | 4 ++++
 sound/firewire/amdtp.h              | 3 +++
 sound/firewire/bebob/bebob_stream.c | 7 +++++++
 3 files changed, 14 insertions(+)

diff --git a/sound/firewire/amdtp.c b/sound/firewire/amdtp.c
index 690c608..e573f25 100644
--- a/sound/firewire/amdtp.c
+++ b/sound/firewire/amdtp.c
@@ -665,6 +665,10 @@ static void handle_in_packet(struct amdtp_stream *s,
 
 	/* Check data block counter continuity */
 	data_block_counter = cip_header[0] & AMDTP_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 == 0) ||
 	    (s->data_block_counter == UINT_MAX)) {
 		lost = false;
diff --git a/sound/firewire/amdtp.h b/sound/firewire/amdtp.h
index c79f058..d8ee7b0 100644
--- a/sound/firewire/amdtp.h
+++ b/sound/firewire/amdtp.h
@@ -27,6 +27,8 @@
  *	skipped for detecting discontinuity.
  * @CIP_SKIP_INIT_DBC_CHECK: Only for in-stream. The value of dbc in first
  *	packet is not continuous from an initial value.
+ * @CIP_EMPTY_HAS_WRONG_DBC: Only for in-stream. The value of dbc in empty
+ *	packet is wrong but the others are correct.
  */
 enum cip_flags {
 	CIP_NONBLOCKING		= 0x00,
@@ -37,6 +39,7 @@ enum cip_flags {
 	CIP_WRONG_DBS		= 0x10,
 	CIP_SKIP_DBC_ZERO_CHECK	= 0x20,
 	CIP_SKIP_INIT_DBC_CHECK	= 0x40,
+	CIP_EMPTY_HAS_WRONG_DBC	= 0x80,
 };
 
 /**
diff --git a/sound/firewire/bebob/bebob_stream.c b/sound/firewire/bebob/bebob_stream.c
index 2695b78..3e74d9b 100644
--- a/sound/firewire/bebob/bebob_stream.c
+++ b/sound/firewire/bebob/bebob_stream.c
@@ -457,6 +457,13 @@ int snd_bebob_stream_init_duplex(struct snd_bebob *bebob)
 	/* See comments in next function */
 	init_completion(&bebob->bus_reset);
 	bebob->tx_stream.flags |= CIP_SKIP_INIT_DBC_CHECK;
+	/*
+	 * At high sampling rate, M-Audio special firmware transmits empty
+	 * packet with the value of dbc incremented by 8 but the others are
+	 * valid to IEC 61883-1.
+	 */
+	if (bebob->maudio_special_quirk)
+		bebob->tx_stream.flags |= CIP_EMPTY_HAS_WRONG_DBC;
 
 	err = amdtp_stream_init(&bebob->rx_stream, bebob->unit,
 				AMDTP_OUT_STREAM, CIP_BLOCKING);
-- 
1.8.3.2