[PATCH v4 1/2] Revert "ALSA: firewire-lib: obsolete workqueue for period update"

[Edmund Raile]

prepare resolution of AB/BA deadlock competition for substream lock:
restore workqueue previously used for process context:

revert commit b5b519965c4c ("ALSA: firewire-lib: obsolete workqueue
for period update")

Cc: stable@xxxxxxxxxxxxxxx
Link: https://lore.kernel.org/r/kwryofzdmjvzkuw6j3clftsxmoolynljztxqwg76hzeo4simnl@jn3eo7pe642q/
Signed-off-by: Edmund Raile <edmund.raile@xxxxxxxxxxxxxx>
---
 sound/firewire/amdtp-stream.c | 15 +++++++++++++++
 sound/firewire/amdtp-stream.h |  1 +
 2 files changed, 16 insertions(+)

diff --git a/sound/firewire/amdtp-stream.c b/sound/firewire/amdtp-stream.c
index d35d0a420ee0..31201d506a21 100644
--- a/sound/firewire/amdtp-stream.c
+++ b/sound/firewire/amdtp-stream.c
@@ -77,6 +77,8 @@
 // overrun. Actual device can skip more, then this module stops the packet streaming.
 #define IR_JUMBO_PAYLOAD_MAX_SKIP_CYCLES	5
 
+static void pcm_period_work(struct work_struct *work);
+
 /**
  * amdtp_stream_init - initialize an AMDTP stream structure
  * @s: the AMDTP stream to initialize
@@ -105,6 +107,7 @@ int amdtp_stream_init(struct amdtp_stream *s, struct fw_unit *unit,
 	s->flags = flags;
 	s->context = ERR_PTR(-1);
 	mutex_init(&s->mutex);
+	INIT_WORK(&s->period_work, pcm_period_work);
 	s->packet_index = 0;
 
 	init_waitqueue_head(&s->ready_wait);
@@ -347,6 +350,7 @@ EXPORT_SYMBOL(amdtp_stream_get_max_payload);
  */
 void amdtp_stream_pcm_prepare(struct amdtp_stream *s)
 {
+	cancel_work_sync(&s->period_work);
 	s->pcm_buffer_pointer = 0;
 	s->pcm_period_pointer = 0;
 }
@@ -624,6 +628,16 @@ static void update_pcm_pointers(struct amdtp_stream *s,
 	}
 }
 
+static void pcm_period_work(struct work_struct *work)
+{
+	struct amdtp_stream *s = container_of(work, struct amdtp_stream,
+					      period_work);
+	struct snd_pcm_substream *pcm = READ_ONCE(s->pcm);
+
+	if (pcm)
+		snd_pcm_period_elapsed(pcm);
+}
+
 static int queue_packet(struct amdtp_stream *s, struct fw_iso_packet *params,
 			bool sched_irq)
 {
@@ -1910,6 +1924,7 @@ static void amdtp_stream_stop(struct amdtp_stream *s)
 		return;
 	}
 
+	cancel_work_sync(&s->period_work);
 	fw_iso_context_stop(s->context);
 	fw_iso_context_destroy(s->context);
 	s->context = ERR_PTR(-1);
diff --git a/sound/firewire/amdtp-stream.h b/sound/firewire/amdtp-stream.h
index a1ed2e80f91a..775db3fc4959 100644
--- a/sound/firewire/amdtp-stream.h
+++ b/sound/firewire/amdtp-stream.h
@@ -191,5 +191,6 @@ struct amdtp_stream {
 
 	/* For a PCM substream processing. */
 	struct snd_pcm_substream *pcm;
+	struct work_struct period_work;
 	snd_pcm_uframes_t pcm_buffer_pointer;
 	unsigned int pcm_period_pointer;
-- 
2.45.2