ALSA: firewire-lib: optimize packet flushing

Trying to flush completed packets is pointless when the pointer
callback was called from the packet completion callback; avoid it.

Signed-off-by: Clemens Ladisch <clemens@ladisch.de>
Signed-off-by: Takashi Iwai <tiwai@suse.de>

2 files changed, 8 insertions, 1 deletions

diff --git a/sound/firewire/amdtp.c b/sound/firewire/amdtp.c
index c2685fbd7366..ea995af6d049 100644
--- a/sound/firewire/amdtp.c
+++ b/sound/firewire/amdtp.c
@@ -178,6 +178,7 @@ void amdtp_out_stream_pcm_prepare(struct amdtp_out_stream *s)
         tasklet_kill(&s->period_tasklet);
         s->pcm_buffer_pointer = 0;
         s->pcm_period_pointer = 0;
+        s->pointer_flush = true;
 }
 EXPORT_SYMBOL(amdtp_out_stream_pcm_prepare);
 
@@ -393,6 +394,7 @@ static void queue_out_packet(struct amdtp_out_stream *s, unsigned int cycle)
                 s->pcm_period_pointer += data_blocks;
                 if (s->pcm_period_pointer >= pcm->runtime->period_size) {
                         s->pcm_period_pointer -= pcm->runtime->period_size;
+                        s->pointer_flush = false;
                         tasklet_hi_schedule(&s->period_tasklet);
                 }
         }
@@ -539,7 +541,11 @@ EXPORT_SYMBOL(amdtp_out_stream_start);
  */
 unsigned long amdtp_out_stream_pcm_pointer(struct amdtp_out_stream *s)
 {
-        fw_iso_context_flush_completions(s->context);
+        /* this optimization is allowed to be racy */
+        if (s->pointer_flush)
+                fw_iso_context_flush_completions(s->context);
+        else
+                s->pointer_flush = true;
 
         return ACCESS_ONCE(s->pcm_buffer_pointer);
 }
diff --git a/sound/firewire/amdtp.h b/sound/firewire/amdtp.h
index 3f13ff63c5d2..b680c5ef01d6 100644
--- a/sound/firewire/amdtp.h
+++ b/sound/firewire/amdtp.h
@@ -68,6 +68,7 @@ struct amdtp_out_stream {
 
         unsigned int pcm_buffer_pointer;
         unsigned int pcm_period_pointer;
+        bool pointer_flush;
 };
 
 int amdtp_out_stream_init(struct amdtp_out_stream *s, struct fw_unit *unit,