ALSA: firewire-lib: cache maximum length of payload to reduce function calls

During packet streaming, maximum length of payload for isochronous packet
is invariable, therefore no need to recalculate. Current ALSA IEC 61883-1/6
engine calls a function to calculate it 8,000 or more times per second
for incoming packet processing.

This commit adds a member to have maximum length of payload into 'struct
amdtp_stream', to reduces the function calls. At first callback from
isochronous context, the length is calculated and stored for later
processing.

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

2 files changed, 6 insertions, 4 deletions

diff --git a/sound/firewire/amdtp-stream.c b/sound/firewire/amdtp-stream.c
index f6af8e64c2cd..9e6f54f8c45d 100644
--- a/sound/firewire/amdtp-stream.c
+++ b/sound/firewire/amdtp-stream.c
@@ -412,8 +412,7 @@ static inline int queue_out_packet(struct amdtp_stream *s,
 
 static inline int queue_in_packet(struct amdtp_stream *s)
 {
-        return queue_packet(s, IN_PACKET_HEADER_SIZE,
-                            amdtp_stream_get_max_payload(s));
+        return queue_packet(s, IN_PACKET_HEADER_SIZE, s->max_payload_length);
 }
 
 static int handle_out_packet(struct amdtp_stream *s,
@@ -713,12 +712,12 @@ static void in_stream_callback(struct fw_iso_context *context, u32 tstamp,
         cycle = decrement_cycle_count(cycle, packets);
 
         /* For buffer-over-run prevention. */
-        max_payload_length = amdtp_stream_get_max_payload(s);
+        max_payload_length = s->max_payload_length;
 
         for (i = 0; i < packets; i++) {
                 cycle = increment_cycle_count(cycle, 1);
 
-                /* The number of quadlets in this packet */
+                /* The number of bytes in this packet */
                 payload_length =
                         (be32_to_cpu(headers[i]) >> ISO_DATA_LENGTH_SHIFT);
                 if (payload_length > max_payload_length) {
@@ -751,6 +750,8 @@ static void amdtp_stream_first_callback(struct fw_iso_context *context,
         u32 cycle;
         unsigned int packets;
 
+        s->max_payload_length = amdtp_stream_get_max_payload(s);
+
         /*
          * For in-stream, first packet has come.
          * For out-stream, prepared to transmit first packet
diff --git a/sound/firewire/amdtp-stream.h b/sound/firewire/amdtp-stream.h
index 2bd4de4c7bb7..7e8831722821 100644
--- a/sound/firewire/amdtp-stream.h
+++ b/sound/firewire/amdtp-stream.h
@@ -110,6 +110,7 @@ struct amdtp_stream {
         int (*handle_packet)(struct amdtp_stream *s,
                         unsigned int payload_quadlets, unsigned int cycle,
                         unsigned int index);
+        unsigned int max_payload_length;
 
         /* For CIP headers. */
         unsigned int source_node_id_field;