ALSA: firewire-lib: handle IT/IR contexts in each software interrupt context

In clause 6.3 of IEC 61883-6:2000, there's an explanation about processing
of presentation timestamp. In the clause, we can see "If a function block
receives a CIP, processes it and subsequently re-transmits it, then the
SYT of the outgoing CIP shall be the sum of the incoming SYT and the
processing delay." ALSA firewire stack has an implementation to partly
satisfy this specification. Developers assumed the stack to perform as an
Audio function block[1].

Following to the assumption, current implementation of ALSA firewire stack
use one software interrupt context to handle both of in/out packets. In
most case, this is processed in 1394 OHCI IR context independently of the
opposite context. Thus, this implementation uses longer CPU time in the
software interrupt context. This is not better for whole system.

Against the assumption, I confirmed that each ASIC for IEC 61883-1/6
doesn't necessarily expect it to the stack. Thus, current implementation
of ALSA firewire stack includes over-engineering.

This commit purges the implementation. As a result, packets of one
direction are handled in one software interrupt context and spends
minimum CPU time.

[1] [alsa-devel] [PATCH 0/8] [RFC] new driver for Echo Audio's Fireworks based devices
http://mailman.alsa-project.org/pipermail/alsa-devel/2013-June/062660.html

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

1 files changed, 7 insertions, 28 deletions

diff --git a/sound/firewire/amdtp-stream.h b/sound/firewire/amdtp-stream.h
index 8775704a3665..da028b0afb48 100644
--- a/sound/firewire/amdtp-stream.h
+++ b/sound/firewire/amdtp-stream.h
@@ -17,8 +17,6 @@
  * @CIP_BLOCKING: In blocking mode, each packet contains either zero or
  *	SYT_INTERVAL samples, with these two types alternating so that
  *	the overall sample rate comes out right.
- * @CIP_SYNC_TO_DEVICE: In sync to device mode, time stamp in out packets is
- *	generated by in packets. Defaultly this driver generates timestamp.
  * @CIP_EMPTY_WITH_TAG0: Only for in-stream. Empty in-packets have TAG0.
  * @CIP_DBC_IS_END_EVENT: Only for in-stream. The value of dbc in an in-packet
  *	corresponds to the end of event in the packet. Out of IEC 61883.
@@ -37,14 +35,13 @@
 enum cip_flags {
 	CIP_NONBLOCKING		= 0x00,
 	CIP_BLOCKING		= 0x01,
-	CIP_SYNC_TO_DEVICE	= 0x02,
-	CIP_EMPTY_WITH_TAG0	= 0x04,
-	CIP_DBC_IS_END_EVENT	= 0x08,
-	CIP_WRONG_DBS		= 0x10,
-	CIP_SKIP_DBC_ZERO_CHECK	= 0x20,
-	CIP_SKIP_INIT_DBC_CHECK	= 0x40,
-	CIP_EMPTY_HAS_WRONG_DBC	= 0x80,
-	CIP_JUMBO_PAYLOAD	= 0x100,
+	CIP_EMPTY_WITH_TAG0	= 0x02,
+	CIP_DBC_IS_END_EVENT	= 0x04,
+	CIP_WRONG_DBS		= 0x08,
+	CIP_SKIP_DBC_ZERO_CHECK	= 0x10,
+	CIP_SKIP_INIT_DBC_CHECK	= 0x20,
+	CIP_EMPTY_HAS_WRONG_DBC	= 0x40,
+	CIP_JUMBO_PAYLOAD	= 0x80,
 };
 
 /**
@@ -137,7 +134,6 @@ struct amdtp_stream {
 	/* To wait for first packet. */
 	bool callbacked;
 	wait_queue_head_t callback_wait;
-	struct amdtp_stream *sync_slave;
 
 	/* For backends to process data blocks. */
 	void *protocol;
@@ -223,23 +219,6 @@ static inline bool cip_sfc_is_base_44100(enum cip_sfc sfc)
 	return sfc & 1;
 }
 
-static inline void amdtp_stream_set_sync(enum cip_flags sync_mode,
-					 struct amdtp_stream *master,
-					 struct amdtp_stream *slave)
-{
-	if (sync_mode == CIP_SYNC_TO_DEVICE) {
-		master->flags |= CIP_SYNC_TO_DEVICE;
-		slave->flags |= CIP_SYNC_TO_DEVICE;
-		master->sync_slave = slave;
-	} else {
-		master->flags &= ~CIP_SYNC_TO_DEVICE;
-		slave->flags &= ~CIP_SYNC_TO_DEVICE;
-		master->sync_slave = NULL;
-	}
-
-	slave->sync_slave = NULL;
-}
-
 /**
  * amdtp_stream_wait_callback - sleep till callbacked or timeout
  * @s: the AMDTP stream