rpmsg: smd: Perform handshake during open

Validate the the remote side is opening the channel that we've found by
performing a handshake when opening the channel.

Tested-by: Will Newton <will.newton@gmail.com>
Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>

drivers/rpmsg/qcom_smd.c

@@ -200,6 +200,7 @@ struct qcom_smd_channel {
 	char *name;
 	enum smd_channel_state state;
 	enum smd_channel_state remote_state;
+	wait_queue_head_t state_change_event;
 
 	struct smd_channel_info_pair *info;
 	struct smd_channel_info_word_pair *info_word;
@@ -570,6 +571,8 @@ static bool qcom_smd_channel_intr(struct qcom_smd_channel *channel)
 	if (remote_state != channel->remote_state) {
 		channel->remote_state = remote_state;
 		need_state_scan = true;
+
+		wake_up_interruptible_all(&channel->state_change_event);
 	}
 	/* Indicate that we have seen any state change */
 	SET_RX_CHANNEL_FLAG(channel, fSTATE, 0);
@@ -786,7 +789,9 @@ out:
 static int qcom_smd_channel_open(struct qcom_smd_channel *channel,
 				 rpmsg_rx_cb_t cb)
 {
+	struct qcom_smd_edge *edge = channel->edge;
 	size_t bb_size;
+	int ret;
 
 	/*
 	 * Packets are maximum 4k, but reduce if the fifo is smaller
@@ -798,9 +803,33 @@ static int qcom_smd_channel_open(struct qcom_smd_channel *channel,
 
 	qcom_smd_channel_set_callback(channel, cb);
 	qcom_smd_channel_set_state(channel, SMD_CHANNEL_OPENING);
+
+	/* Wait for remote to enter opening or opened */
+	ret = wait_event_interruptible_timeout(channel->state_change_event,
+			channel->remote_state == SMD_CHANNEL_OPENING ||
+			channel->remote_state == SMD_CHANNEL_OPENED,
+			HZ);
+	if (!ret) {
+		dev_err(&edge->dev, "remote side did not enter opening state\n");
+		goto out_close_timeout;
+	}
+
 	qcom_smd_channel_set_state(channel, SMD_CHANNEL_OPENED);
 
+	/* Wait for remote to enter opened */
+	ret = wait_event_interruptible_timeout(channel->state_change_event,
+			channel->remote_state == SMD_CHANNEL_OPENED,
+			HZ);
+	if (!ret) {
+		dev_err(&edge->dev, "remote side did not enter open state\n");
+		goto out_close_timeout;
+	}
+
 	return 0;
+
+out_close_timeout:
+	qcom_smd_channel_set_state(channel, SMD_CHANNEL_CLOSED);
+	return -ETIMEDOUT;
 }
 
 /*
@@ -1055,6 +1084,7 @@ static struct qcom_smd_channel *qcom_smd_create_channel(struct qcom_smd_edge *ed
 	mutex_init(&channel->tx_lock);
 	spin_lock_init(&channel->recv_lock);
 	init_waitqueue_head(&channel->fblockread_event);
+	init_waitqueue_head(&channel->state_change_event);
 
 	info = qcom_smem_get(edge->remote_pid, smem_info_item, &info_size);
 	if (IS_ERR(info)) {