[RFC 03/12] ASoC: SOF: support IPC with immediate response

[Guennadi Liakhovetski <guennadi.liakhovetski@linux.intel.com>]

Usually when an IPC message is sent, we have to wait for a reply from
the DSP or from the host in the VirtIO case. However, sometimes in
the VirtIO case a response is available immediately. Skip sleeping in
such cases.

Signed-off-by: Guennadi Liakhovetski <guennadi.liakhovetski@linux.intel.com>
---
 sound/soc/sof/ipc.c | 11 +++++++----
 sound/soc/sof/ops.h | 10 +++++++++-
 2 files changed, 16 insertions(+), 5 deletions(-)

diff --git a/sound/soc/sof/ipc.c b/sound/soc/sof/ipc.c
index f7a0353..b3e1587 100644
--- a/sound/soc/sof/ipc.c
+++ b/sound/soc/sof/ipc.c
@@ -262,6 +262,12 @@ static int sof_ipc_tx_message_unlocked(struct snd_sof_ipc *ipc, u32 header,
 
 	sdev->msg = msg;
 
+	/*
+	 * If snd_sof_dsp_send_msg() returns a positive number it means, that a
+	 * response is already available, no need to sleep waiting for it. In
+	 * such a case msg->ipc_complete will stay true and tx_wait_done() will
+	 * return immediately.
+	 */
 	ret = snd_sof_dsp_send_msg(sdev, msg);
 	/* Next reply that we receive will be related to this message */
 	if (!ret)
@@ -279,10 +285,7 @@ static int sof_ipc_tx_message_unlocked(struct snd_sof_ipc *ipc, u32 header,
 	ipc_log_header(sdev->dev, "ipc tx", msg->header);
 
 	/* now wait for completion */
-	if (!ret)
-		ret = tx_wait_done(ipc, msg, reply_data);
-
-	return ret;
+	return tx_wait_done(ipc, msg, reply_data);
 }
 
 /* send IPC message from host to DSP */
diff --git a/sound/soc/sof/ops.h b/sound/soc/sof/ops.h
index b21632f..bf91467 100644
--- a/sound/soc/sof/ops.h
+++ b/sound/soc/sof/ops.h
@@ -274,7 +274,15 @@ static inline void snd_sof_dsp_block_write(struct snd_sof_dev *sdev, u32 bar,
 	sof_ops(sdev)->block_write(sdev, bar, offset, src, bytes);
 }
 
-/* ipc */
+/**
+ * snd_sof_dsp_send_msg - call sdev ops to send a message
+ * @sdev:	sdev context
+ * @msg:	message to send
+ *
+ * Returns	< 0 - an error code
+ *		  0 - the message has been sent, wait for a reply
+ *		> 0 - the message has been sent, a reply is already available
+ */
 static inline int snd_sof_dsp_send_msg(struct snd_sof_dev *sdev,
 				       struct snd_sof_ipc_msg *msg)
 {
-- 
1.9.3