diff --git a/drivers/mailbox/Kconfig b/drivers/mailbox/Kconfig
index c5731e5e3c6c..ba2f1525f4ee 100644
--- a/drivers/mailbox/Kconfig
+++ b/drivers/mailbox/Kconfig
@@ -163,9 +163,10 @@ config BCM_PDC_MBOX
 config BCM_FLEXRM_MBOX
 	tristate "Broadcom FlexRM Mailbox"
 	depends on ARM64
+	depends on ARCH_BCM_IPROC || COMPILE_TEST
 	depends on HAS_DMA
 	select GENERIC_MSI_IRQ_DOMAIN
-	default ARCH_BCM_IPROC
+	default m if ARCH_BCM_IPROC
 	help
 	  Mailbox implementation of the Broadcom FlexRM ring manager,
 	  which provides access to various offload engines on Broadcom
diff --git a/drivers/mailbox/bcm-flexrm-mailbox.c b/drivers/mailbox/bcm-flexrm-mailbox.c
index ae6146311934..a8cf4333a68f 100644
--- a/drivers/mailbox/bcm-flexrm-mailbox.c
+++ b/drivers/mailbox/bcm-flexrm-mailbox.c
@@ -1,10 +1,18 @@
-/* Broadcom FlexRM Mailbox Driver
- *
+/*
  * Copyright (C) 2017 Broadcom
  *
- * This program is free software; you can redistribute it and/or modify
- * it under the terms of the GNU General Public License version 2 as
- * published by the Free Software Foundation.
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License as
+ * published by the Free Software Foundation version 2.
+ *
+ * This program is distributed "as is" WITHOUT ANY WARRANTY of any
+ * kind, whether express or implied; without even the implied warranty
+ * of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ */
+
+/*
+ * Broadcom FlexRM Mailbox Driver
  *
  * Each Broadcom FlexSparx4 offload engine is implemented as an
  * extension to Broadcom FlexRM ring manager. The FlexRM ring
@@ -1116,8 +1124,8 @@ static int flexrm_process_completions(struct flexrm_ring *ring)
 		err = flexrm_cmpl_desc_to_error(desc);
 		if (err < 0) {
 			dev_warn(ring->mbox->dev,
-				 "got completion desc=0x%lx with error %d",
-				 (unsigned long)desc, err);
+			"ring%d got completion desc=0x%lx with error %d\n",
+			ring->num, (unsigned long)desc, err);
 		}
 
 		/* Determine request id from completion descriptor */
@@ -1127,8 +1135,8 @@ static int flexrm_process_completions(struct flexrm_ring *ring)
 		msg = ring->requests[reqid];
 		if (!msg) {
 			dev_warn(ring->mbox->dev,
-				 "null msg pointer for completion desc=0x%lx",
-				 (unsigned long)desc);
+			"ring%d null msg pointer for completion desc=0x%lx\n",
+			ring->num, (unsigned long)desc);
 			continue;
 		}
 
@@ -1238,7 +1246,9 @@ static int flexrm_startup(struct mbox_chan *chan)
 	ring->bd_base = dma_pool_alloc(ring->mbox->bd_pool,
 				       GFP_KERNEL, &ring->bd_dma_base);
 	if (!ring->bd_base) {
-		dev_err(ring->mbox->dev, "can't allocate BD memory\n");
+		dev_err(ring->mbox->dev,
+			"can't allocate BD memory for ring%d\n",
+			ring->num);
 		ret = -ENOMEM;
 		goto fail;
 	}
@@ -1261,7 +1271,9 @@ static int flexrm_startup(struct mbox_chan *chan)
 	ring->cmpl_base = dma_pool_alloc(ring->mbox->cmpl_pool,
 					 GFP_KERNEL, &ring->cmpl_dma_base);
 	if (!ring->cmpl_base) {
-		dev_err(ring->mbox->dev, "can't allocate completion memory\n");
+		dev_err(ring->mbox->dev,
+			"can't allocate completion memory for ring%d\n",
+			ring->num);
 		ret = -ENOMEM;
 		goto fail_free_bd_memory;
 	}
@@ -1269,7 +1281,8 @@ static int flexrm_startup(struct mbox_chan *chan)
 
 	/* Request IRQ */
 	if (ring->irq == UINT_MAX) {
-		dev_err(ring->mbox->dev, "ring IRQ not available\n");
+		dev_err(ring->mbox->dev,
+			"ring%d IRQ not available\n", ring->num);
 		ret = -ENODEV;
 		goto fail_free_cmpl_memory;
 	}
@@ -1278,7 +1291,8 @@ static int flexrm_startup(struct mbox_chan *chan)
 				   flexrm_irq_thread,
 				   0, dev_name(ring->mbox->dev), ring);
 	if (ret) {
-		dev_err(ring->mbox->dev, "failed to request ring IRQ\n");
+		dev_err(ring->mbox->dev,
+			"failed to request ring%d IRQ\n", ring->num);
 		goto fail_free_cmpl_memory;
 	}
 	ring->irq_requested = true;
@@ -1291,7 +1305,9 @@ static int flexrm_startup(struct mbox_chan *chan)
 			&ring->irq_aff_hint);
 	ret = irq_set_affinity_hint(ring->irq, &ring->irq_aff_hint);
 	if (ret) {
-		dev_err(ring->mbox->dev, "failed to set IRQ affinity hint\n");
+		dev_err(ring->mbox->dev,
+			"failed to set IRQ affinity hint for ring%d\n",
+			ring->num);
 		goto fail_free_irq;
 	}
 
@@ -1365,8 +1381,8 @@ static void flexrm_shutdown(struct mbox_chan *chan)
 	/* Disable/inactivate ring */
 	writel_relaxed(0x0, ring->regs + RING_CONTROL);
 
-	/* Flush ring with timeout of 1s */
-	timeout = 1000;
+	/* Set ring flush state */
+	timeout = 1000; /* timeout of 1s */
 	writel_relaxed(BIT(CONTROL_FLUSH_SHIFT),
 			ring->regs + RING_CONTROL);
 	do {
@@ -1374,7 +1390,23 @@ static void flexrm_shutdown(struct mbox_chan *chan)
 		    FLUSH_DONE_MASK)
 			break;
 		mdelay(1);
-	} while (timeout--);
+	} while (--timeout);
+	if (!timeout)
+		dev_err(ring->mbox->dev,
+			"setting ring%d flush state timedout\n", ring->num);
+
+	/* Clear ring flush state */
+	timeout = 1000; /* timeout of 1s */
+	writel_relaxed(0x0, ring + RING_CONTROL);
+	do {
+		if (!(readl_relaxed(ring + RING_FLUSH_DONE) &
+		      FLUSH_DONE_MASK))
+			break;
+		mdelay(1);
+	} while (--timeout);
+	if (!timeout)
+		dev_err(ring->mbox->dev,
+			"clearing ring%d flush state timedout\n", ring->num);
 
 	/* Abort all in-flight requests */
 	for (reqid = 0; reqid < RING_MAX_REQ_COUNT; reqid++) {
diff --git a/drivers/mailbox/mailbox-test.c b/drivers/mailbox/mailbox-test.c
index 97fb956bb6e0..93f3d4d61fa7 100644
--- a/drivers/mailbox/mailbox-test.c
+++ b/drivers/mailbox/mailbox-test.c
@@ -30,6 +30,7 @@
 #define MBOX_HEXDUMP_MAX_LEN	(MBOX_HEXDUMP_LINE_LEN *		\
 				 (MBOX_MAX_MSG_LEN / MBOX_BYTES_PER_LINE))
 
+static bool mbox_data_ready;
 static struct dentry *root_debugfs_dir;
 
 struct mbox_test_device {
@@ -152,16 +153,14 @@ out:
 
 static bool mbox_test_message_data_ready(struct mbox_test_device *tdev)
 {
-	unsigned char data;
+	bool data_ready;
 	unsigned long flags;
 
 	spin_lock_irqsave(&tdev->lock, flags);
-	data = tdev->rx_buffer[0];
+	data_ready = mbox_data_ready;
 	spin_unlock_irqrestore(&tdev->lock, flags);
 
-	if (data != '\0')
-		return true;
-	return false;
+	return data_ready;
 }
 
 static ssize_t mbox_test_message_read(struct file *filp, char __user *userbuf,
@@ -223,6 +222,7 @@ static ssize_t mbox_test_message_read(struct file *filp, char __user *userbuf,
 	*(touser + l) = '\0';
 
 	memset(tdev->rx_buffer, 0, MBOX_MAX_MSG_LEN);
+	mbox_data_ready = false;
 
 	spin_unlock_irqrestore(&tdev->lock, flags);
 
@@ -292,6 +292,7 @@ static void mbox_test_receive_message(struct mbox_client *client, void *message)
 				     message, MBOX_MAX_MSG_LEN);
 		memcpy(tdev->rx_buffer, message, MBOX_MAX_MSG_LEN);
 	}
+	mbox_data_ready = true;
 	spin_unlock_irqrestore(&tdev->lock, flags);
 
 	wake_up_interruptible(&tdev->waitq);
diff --git a/drivers/mailbox/mailbox.c b/drivers/mailbox/mailbox.c
index 537f4f6d009b..674b35f402f5 100644
--- a/drivers/mailbox/mailbox.c
+++ b/drivers/mailbox/mailbox.c
@@ -351,7 +351,7 @@ struct mbox_chan *mbox_request_channel(struct mbox_client *cl, int index)
 	init_completion(&chan->tx_complete);
 
 	if (chan->txdone_method	== TXDONE_BY_POLL && cl->knows_txdone)
-		chan->txdone_method |= TXDONE_BY_ACK;
+		chan->txdone_method = TXDONE_BY_ACK;
 
 	spin_unlock_irqrestore(&chan->lock, flags);
 
@@ -418,7 +418,7 @@ void mbox_free_channel(struct mbox_chan *chan)
 	spin_lock_irqsave(&chan->lock, flags);
 	chan->cl = NULL;
 	chan->active_req = NULL;
-	if (chan->txdone_method == (TXDONE_BY_POLL | TXDONE_BY_ACK))
+	if (chan->txdone_method == TXDONE_BY_ACK)
 		chan->txdone_method = TXDONE_BY_POLL;
 
 	module_put(chan->mbox->dev->driver->owner);
diff --git a/drivers/mailbox/omap-mailbox.c b/drivers/mailbox/omap-mailbox.c
index c5e8b9cb170d..2517038a8452 100644
--- a/drivers/mailbox/omap-mailbox.c
+++ b/drivers/mailbox/omap-mailbox.c
@@ -906,7 +906,11 @@ static int __init omap_mbox_init(void)
 	mbox_kfifo_size = max_t(unsigned int, mbox_kfifo_size,
 							sizeof(mbox_msg_t));
 
-	return platform_driver_register(&omap_mbox_driver);
+	err = platform_driver_register(&omap_mbox_driver);
+	if (err)
+		class_unregister(&omap_mbox_class);
+
+	return err;
 }
 subsys_initcall(omap_mbox_init);
 
diff --git a/drivers/mailbox/pcc.c b/drivers/mailbox/pcc.c
index e5a69679cfa2..3ef7f036ceea 100644
--- a/drivers/mailbox/pcc.c
+++ b/drivers/mailbox/pcc.c
@@ -265,7 +265,7 @@ struct mbox_chan *pcc_mbox_request_channel(struct mbox_client *cl,
 	init_completion(&chan->tx_complete);
 
 	if (chan->txdone_method == TXDONE_BY_POLL && cl->knows_txdone)
-		chan->txdone_method |= TXDONE_BY_ACK;
+		chan->txdone_method = TXDONE_BY_ACK;
 
 	spin_unlock_irqrestore(&chan->lock, flags);
 
@@ -311,7 +311,7 @@ void pcc_mbox_free_channel(struct mbox_chan *chan)
 	spin_lock_irqsave(&chan->lock, flags);
 	chan->cl = NULL;
 	chan->active_req = NULL;
-	if (chan->txdone_method == (TXDONE_BY_POLL | TXDONE_BY_ACK))
+	if (chan->txdone_method == TXDONE_BY_ACK)
 		chan->txdone_method = TXDONE_BY_POLL;
 
 	spin_unlock_irqrestore(&chan->lock, flags);