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, 4 insertions, 36 deletions

diff --git a/sound/firewire/amdtp-stream.c b/sound/firewire/amdtp-stream.c
index a22e5594d2ed..3468419259a0 100644
--- a/sound/firewire/amdtp-stream.c
+++ b/sound/firewire/amdtp-stream.c
@@ -91,7 +91,6 @@ int amdtp_stream_init(struct amdtp_stream *s, struct fw_unit *unit,
 
 	init_waitqueue_head(&s->callback_wait);
 	s->callbacked = false;
-	s->sync_slave = NULL;
 
 	s->fmt = fmt;
 	s->process_data_blocks = process_data_blocks;
@@ -650,54 +649,25 @@ static void in_stream_callback(struct fw_iso_context *context, u32 tstamp,
 			dev_err(&s->unit->device,
 				"Detect jumbo payload: %02x %02x\n",
 				payload_quadlets, max_payload_quadlets);
-			s->packet_index = -1;
 			break;
 		}
 
 		syt = be32_to_cpu(buffer[1]) & CIP_SYT_MASK;
 		if (handle_in_packet(s, payload_quadlets, buffer,
-						&data_blocks, cycle, syt) < 0) {
-			s->packet_index = -1;
+						&data_blocks, cycle, syt) < 0)
 			break;
-		}
-
-		/* Process sync slave stream */
-		if (s->sync_slave && s->sync_slave->callbacked) {
-			if (handle_out_packet(s->sync_slave,
-					      data_blocks, cycle, syt) < 0) {
-				s->packet_index = -1;
-				break;
-			}
-		}
 	}
 
-	/* Queueing error or detecting discontinuity */
-	if (s->packet_index < 0) {
+	/* Queueing error or detecting invalid payload. */
+	if (p < packets) {
+		s->packet_index = -1;
 		amdtp_stream_pcm_abort(s);
-
-		/* Abort sync slave. */
-		if (s->sync_slave) {
-			s->sync_slave->packet_index = -1;
-			amdtp_stream_pcm_abort(s->sync_slave);
-		}
 		return;
 	}
 
-	/* when sync to device, flush the packets for slave stream */
-	if (s->sync_slave && s->sync_slave->callbacked)
-		fw_iso_context_queue_flush(s->sync_slave->context);
-
 	fw_iso_context_queue_flush(s->context);
 }
 
-/* processing is done by master callback */
-static void slave_stream_callback(struct fw_iso_context *context, u32 tstamp,
-				  size_t header_length, void *header,
-				  void *private_data)
-{
-	return;
-}
-
 /* this is executed one time */
 static void amdtp_stream_first_callback(struct fw_iso_context *context,
 					u32 tstamp, size_t header_length,
@@ -714,8 +684,6 @@ static void amdtp_stream_first_callback(struct fw_iso_context *context,
 
 	if (s->direction == AMDTP_IN_STREAM)
 		context->callback.sc = in_stream_callback;
-	else if (s->flags & CIP_SYNC_TO_DEVICE)
-		context->callback.sc = slave_stream_callback;
 	else
 		context->callback.sc = out_stream_callback;