diff --git a/drivers/net/can/flexcan.c b/drivers/net/can/flexcan.c
index 0431f8d..677c417 100644
--- a/drivers/net/can/flexcan.c
+++ b/drivers/net/can/flexcan.c
@@ -135,13 +135,12 @@
 
 /* FLEXCAN interrupt flag register (IFLAG) bits */
 /* Errata ERR005829 step7: Reserve first valid MB */
-#define FLEXCAN_TX_MB_RESERVED_OFF_FIFO	8
-#define FLEXCAN_TX_MB_OFF_FIFO		9
+#define FLEXCAN_TX_MB_RESERVED_OFF_FIFO		8
 #define FLEXCAN_TX_MB_RESERVED_OFF_TIMESTAMP	0
-#define FLEXCAN_TX_MB_OFF_TIMESTAMP		1
-#define FLEXCAN_RX_MB_OFF_TIMESTAMP_FIRST	(FLEXCAN_TX_MB_OFF_TIMESTAMP + 1)
-#define FLEXCAN_RX_MB_OFF_TIMESTAMP_LAST	63
-#define FLEXCAN_IFLAG_MB(x)		BIT(x)
+#define FLEXCAN_TX_MB				63
+#define FLEXCAN_RX_MB_OFF_TIMESTAMP_FIRST	(FLEXCAN_TX_MB_RESERVED_OFF_TIMESTAMP + 1)
+#define FLEXCAN_RX_MB_OFF_TIMESTAMP_LAST	(FLEXCAN_TX_MB - 1)
+#define FLEXCAN_IFLAG_MB(x)		BIT(x & 0x1f)
 #define FLEXCAN_IFLAG_RX_FIFO_OVERFLOW	BIT(7)
 #define FLEXCAN_IFLAG_RX_FIFO_WARN	BIT(6)
 #define FLEXCAN_IFLAG_RX_FIFO_AVAILABLE	BIT(5)
@@ -737,9 +736,9 @@ static inline u64 flexcan_read_reg_iflag_rx(struct flexcan_priv *priv)
 	struct flexcan_regs __iomem *regs = priv->regs;
 	u32 iflag1, iflag2;
 
-	iflag2 = priv->read(&regs->iflag2) & priv->reg_imask2_default;
-	iflag1 = priv->read(&regs->iflag1) & priv->reg_imask1_default &
+	iflag2 = priv->read(&regs->iflag2) & priv->reg_imask2_default &
 		~FLEXCAN_IFLAG_MB(priv->tx_mb_idx);
+	iflag1 = priv->read(&regs->iflag1) & priv->reg_imask1_default;
 
 	return (u64)iflag2 << 32 | iflag1;
 }
@@ -751,11 +750,9 @@ static irqreturn_t flexcan_irq(int irq, void *dev_id)
 	struct flexcan_priv *priv = netdev_priv(dev);
 	struct flexcan_regs __iomem *regs = priv->regs;
 	irqreturn_t handled = IRQ_NONE;
-	u32 reg_iflag1, reg_esr;
+	u32 reg_iflag2, reg_esr;
 	enum can_state last_state = priv->can.state;
 
-	reg_iflag1 = priv->read(&regs->iflag1);
-
 	/* reception interrupt */
 	if (priv->devtype_data->quirks & FLEXCAN_QUIRK_USE_OFF_TIMESTAMP) {
 		u64 reg_iflag;
@@ -769,6 +766,9 @@ static irqreturn_t flexcan_irq(int irq, void *dev_id)
 				break;
 		}
 	} else {
+		u32 reg_iflag1;
+
+		reg_iflag1 = priv->read(&regs->iflag1);
 		if (reg_iflag1 & FLEXCAN_IFLAG_RX_FIFO_AVAILABLE) {
 			handled = IRQ_HANDLED;
 			can_rx_offload_irq_offload_fifo(&priv->offload);
@@ -784,8 +784,10 @@ static irqreturn_t flexcan_irq(int irq, void *dev_id)
 		}
 	}
 
+	reg_iflag2 = priv->read(&regs->iflag2);
+
 	/* transmission complete interrupt */
-	if (reg_iflag1 & FLEXCAN_IFLAG_MB(priv->tx_mb_idx)) {
+	if (reg_iflag2 & FLEXCAN_IFLAG_MB(priv->tx_mb_idx)) {
 		handled = IRQ_HANDLED;
 		stats->tx_bytes += can_get_echo_skb(dev, 0);
 		stats->tx_packets++;
@@ -794,7 +796,7 @@ static irqreturn_t flexcan_irq(int irq, void *dev_id)
 		/* after sending a RTR frame MB is in RX mode */
 		priv->write(FLEXCAN_MB_CODE_TX_INACTIVE,
 			    &priv->tx_mb->can_ctrl);
-		priv->write(FLEXCAN_IFLAG_MB(priv->tx_mb_idx), &regs->iflag1);
+		priv->write(FLEXCAN_IFLAG_MB(priv->tx_mb_idx), &regs->iflag2);
 		netif_wake_queue(dev);
 	}
 
@@ -936,15 +938,13 @@ static int flexcan_chip_start(struct net_device *dev)
 	reg_mcr &= ~FLEXCAN_MCR_MAXMB(0xff);
 	reg_mcr |= FLEXCAN_MCR_FRZ | FLEXCAN_MCR_HALT | FLEXCAN_MCR_SUPV |
 		FLEXCAN_MCR_WRN_EN | FLEXCAN_MCR_SRX_DIS | FLEXCAN_MCR_IRMQ |
-		FLEXCAN_MCR_IDAM_C;
+		FLEXCAN_MCR_IDAM_C | FLEXCAN_MCR_MAXMB(priv->tx_mb_idx);
 
-	if (priv->devtype_data->quirks & FLEXCAN_QUIRK_USE_OFF_TIMESTAMP) {
+	if (priv->devtype_data->quirks & FLEXCAN_QUIRK_USE_OFF_TIMESTAMP)
 		reg_mcr &= ~FLEXCAN_MCR_FEN;
-		reg_mcr |= FLEXCAN_MCR_MAXMB(priv->offload.mb_last);
-	} else {
-		reg_mcr |= FLEXCAN_MCR_FEN |
-			FLEXCAN_MCR_MAXMB(priv->tx_mb_idx);
-	}
+	else
+		reg_mcr |= FLEXCAN_MCR_FEN;
+
 	netdev_dbg(dev, "%s: writing mcr=0x%08x", __func__, reg_mcr);
 	priv->write(reg_mcr, &regs->mcr);
 
@@ -987,16 +987,17 @@ static int flexcan_chip_start(struct net_device *dev)
 		priv->write(reg_ctrl2, &regs->ctrl2);
 	}
 
-	/* clear and invalidate all mailboxes first */
-	for (i = priv->tx_mb_idx; i < ARRAY_SIZE(regs->mb); i++) {
-		priv->write(FLEXCAN_MB_CODE_RX_INACTIVE,
-			    &regs->mb[i].can_ctrl);
-	}
-
 	if (priv->devtype_data->quirks & FLEXCAN_QUIRK_USE_OFF_TIMESTAMP) {
-		for (i = priv->offload.mb_first; i <= priv->offload.mb_last; i++)
+		for (i = priv->offload.mb_first; i <= priv->offload.mb_last; i++) {
 			priv->write(FLEXCAN_MB_CODE_RX_EMPTY,
 				    &regs->mb[i].can_ctrl);
+		}
+	} else {
+		/* clear and invalidate unused mailboxes first */
+		for (i = FLEXCAN_TX_MB_RESERVED_OFF_FIFO; i <= ARRAY_SIZE(regs->mb); i++) {
+			priv->write(FLEXCAN_MB_CODE_RX_INACTIVE,
+				    &regs->mb[i].can_ctrl);
+		}
 	}
 
 	/* Errata ERR005829: mark first TX mailbox as INACTIVE */
@@ -1360,17 +1361,15 @@ static int flexcan_probe(struct platform_device *pdev)
 	priv->devtype_data = devtype_data;
 	priv->reg_xceiver = reg_xceiver;
 
-	if (priv->devtype_data->quirks & FLEXCAN_QUIRK_USE_OFF_TIMESTAMP) {
-		priv->tx_mb_idx = FLEXCAN_TX_MB_OFF_TIMESTAMP;
+	if (priv->devtype_data->quirks & FLEXCAN_QUIRK_USE_OFF_TIMESTAMP)
 		priv->tx_mb_reserved = &regs->mb[FLEXCAN_TX_MB_RESERVED_OFF_TIMESTAMP];
-	} else {
-		priv->tx_mb_idx = FLEXCAN_TX_MB_OFF_FIFO;
+	else
 		priv->tx_mb_reserved = &regs->mb[FLEXCAN_TX_MB_RESERVED_OFF_FIFO];
-	}
+	priv->tx_mb_idx = FLEXCAN_TX_MB;
 	priv->tx_mb = &regs->mb[priv->tx_mb_idx];
 
-	priv->reg_imask1_default = FLEXCAN_IFLAG_MB(priv->tx_mb_idx);
-	priv->reg_imask2_default = 0;
+	priv->reg_imask1_default = 0;
+	priv->reg_imask2_default = FLEXCAN_IFLAG_MB(priv->tx_mb_idx);
 
 	priv->offload.mailbox_read = flexcan_mailbox_read;