diff --git a/drivers/spi/atmel-quadspi.c b/drivers/spi/atmel-quadspi.c
index 5fd929e..1e63fd4 100644
--- a/drivers/spi/atmel-quadspi.c
+++ b/drivers/spi/atmel-quadspi.c
@@ -173,6 +173,81 @@
 	{ 4, 4, 4, QSPI_IFR_WIDTH_QUAD_CMD },
 };
 
+#ifdef VERBOSE_DEBUG
+static const char *atmel_qspi_reg_name(u32 offset, char *tmp, size_t sz)
+{
+	switch (offset) {
+	case QSPI_CR:
+		return "CR";
+	case QSPI_MR:
+		return "MR";
+	case QSPI_RD:
+		return "MR";
+	case QSPI_TD:
+		return "TD";
+	case QSPI_SR:
+		return "SR";
+	case QSPI_IER:
+		return "IER";
+	case QSPI_IDR:
+		return "IDR";
+	case QSPI_IMR:
+		return "IMR";
+	case QSPI_SCR:
+		return "SCR";
+	case QSPI_IAR:
+		return "IAR";
+	case QSPI_ICR:
+		return "ICR/WICR";
+	case QSPI_IFR:
+		return "IFR";
+	case QSPI_RICR:
+		return "RICR";
+	case QSPI_SMR:
+		return "SMR";
+	case QSPI_SKR:
+		return "SKR";
+	case QSPI_WPMR:
+		return "WPMR";
+	case QSPI_WPSR:
+		return "WPSR";
+	case QSPI_VERSION:
+		return "VERSION";
+	default:
+		snprintf(tmp, sz, "0x%02x", offset);
+		break;
+	}
+
+	return tmp;
+}
+#endif /* VERBOSE_DEBUG */
+
+static u32 atmel_qspi_read(struct atmel_qspi *aq, u32 offset)
+{
+	u32 value = readl_relaxed(aq->regs + offset);
+
+#ifdef VERBOSE_DEBUG
+	char tmp[8];
+
+	dev_vdbg(&aq->pdev->dev, "read 0x%08x from %s\n", value,
+		 atmel_qspi_reg_name(offset, tmp, sizeof(tmp)));
+#endif /* VERBOSE_DEBUG */
+
+	return value;
+}
+
+static void atmel_qspi_write(u32 value, struct atmel_qspi *aq, u32 offset)
+{
+#ifdef VERBOSE_DEBUG
+	char tmp[8];
+
+	dev_vdbg(&aq->pdev->dev, "write 0x%08x into %s\n", value,
+		 atmel_qspi_reg_name(offset, tmp, sizeof(tmp)));
+#endif /* VERBOSE_DEBUG */
+
+	writel_relaxed(value, aq->regs + offset);
+}
+
 static inline bool atmel_qspi_is_compatible(const struct spi_mem_op *op,
 					    const struct atmel_qspi_mode *mode)
 {
@@ -210,6 +285,12 @@
 		op->dummy.nbytes == 0)
 		return false;
 
+	/* DTR ops not supported. */
+	if (op->cmd.dtr || op->addr.dtr || op->dummy.dtr || op->data.dtr)
+		return false;
+	if (op->cmd.nbytes != 1)
+		return false;
+
 	return true;
 }
 
@@ -297,32 +378,32 @@
 	 * Serial Memory Mode (SMM).
 	 */
 	if (aq->mr != QSPI_MR_SMM) {
-		writel_relaxed(QSPI_MR_SMM, aq->regs + QSPI_MR);
+		atmel_qspi_write(QSPI_MR_SMM, aq, QSPI_MR);
 		aq->mr = QSPI_MR_SMM;
 	}
 
 	/* Clear pending interrupts */
-	(void)readl_relaxed(aq->regs + QSPI_SR);
+	(void)atmel_qspi_read(aq, QSPI_SR);
 
 	if (aq->caps->has_ricr) {
 		if (!op->addr.nbytes && op->data.dir == SPI_MEM_DATA_IN)
 			ifr |= QSPI_IFR_APBTFRTYP_READ;
 
 		/* Set QSPI Instruction Frame registers */
-		writel_relaxed(iar, aq->regs + QSPI_IAR);
+		atmel_qspi_write(iar, aq, QSPI_IAR);
 		if (op->data.dir == SPI_MEM_DATA_IN)
-			writel_relaxed(icr, aq->regs + QSPI_RICR);
+			atmel_qspi_write(icr, aq, QSPI_RICR);
 		else
-			writel_relaxed(icr, aq->regs + QSPI_WICR);
-		writel_relaxed(ifr, aq->regs + QSPI_IFR);
+			atmel_qspi_write(icr, aq, QSPI_WICR);
+		atmel_qspi_write(ifr, aq, QSPI_IFR);
 	} else {
 		if (op->data.nbytes && op->data.dir == SPI_MEM_DATA_OUT)
 			ifr |= QSPI_IFR_SAMA5D2_WRITE_TRSFR;
 
 		/* Set QSPI Instruction Frame registers */
-		writel_relaxed(iar, aq->regs + QSPI_IAR);
-		writel_relaxed(icr, aq->regs + QSPI_ICR);
-		writel_relaxed(ifr, aq->regs + QSPI_IFR);
+		atmel_qspi_write(iar, aq, QSPI_IAR);
+		atmel_qspi_write(icr, aq, QSPI_ICR);
+		atmel_qspi_write(ifr, aq, QSPI_IFR);
 	}
 
 	return 0;
@@ -349,33 +430,33 @@
 	/* Skip to the final steps if there is no data */
 	if (op->data.nbytes) {
 		/* Dummy read of QSPI_IFR to synchronize APB and AHB accesses */
-		(void)readl_relaxed(aq->regs + QSPI_IFR);
+		(void)atmel_qspi_read(aq, QSPI_IFR);
 
 		/* Send/Receive data */
 		if (op->data.dir == SPI_MEM_DATA_IN)
-			_memcpy_fromio(op->data.buf.in, aq->mem + offset,
-				       op->data.nbytes);
+			memcpy_fromio(op->data.buf.in, aq->mem + offset,
+				      op->data.nbytes);
 		else
-			_memcpy_toio(aq->mem + offset, op->data.buf.out,
-				     op->data.nbytes);
+			memcpy_toio(aq->mem + offset, op->data.buf.out,
+				    op->data.nbytes);
 
 		/* Release the chip-select */
-		writel_relaxed(QSPI_CR_LASTXFER, aq->regs + QSPI_CR);
+		atmel_qspi_write(QSPI_CR_LASTXFER, aq, QSPI_CR);
 	}
 
 	/* Poll INSTRuction End status */
-	sr = readl_relaxed(aq->regs + QSPI_SR);
+	sr = atmel_qspi_read(aq, QSPI_SR);
 	if ((sr & QSPI_SR_CMD_COMPLETED) == QSPI_SR_CMD_COMPLETED)
 		return err;
 
 	/* Wait for INSTRuction End interrupt */
 	reinit_completion(&aq->cmd_completion);
 	aq->pending = sr & QSPI_SR_CMD_COMPLETED;
-	writel_relaxed(QSPI_SR_CMD_COMPLETED, aq->regs + QSPI_IER);
+	atmel_qspi_write(QSPI_SR_CMD_COMPLETED, aq, QSPI_IER);
 	if (!wait_for_completion_timeout(&aq->cmd_completion,
 					 msecs_to_jiffies(1000)))
 		err = -ETIMEDOUT;
-	writel_relaxed(QSPI_SR_CMD_COMPLETED, aq->regs + QSPI_IDR);
+	atmel_qspi_write(QSPI_SR_CMD_COMPLETED, aq, QSPI_IDR);
 
 	return err;
 }
@@ -414,7 +495,7 @@
 		scbr--;
 
 	aq->scr = QSPI_SCR_SCBR(scbr);
-	writel_relaxed(aq->scr, aq->regs + QSPI_SCR);
+	atmel_qspi_write(aq->scr, aq, QSPI_SCR);
 
 	return 0;
 }
@@ -422,14 +503,14 @@
 static void atmel_qspi_init(struct atmel_qspi *aq)
 {
 	/* Reset the QSPI controller */
-	writel_relaxed(QSPI_CR_SWRST, aq->regs + QSPI_CR);
+	atmel_qspi_write(QSPI_CR_SWRST, aq, QSPI_CR);
 
 	/* Set the QSPI controller by default in Serial Memory Mode */
-	writel_relaxed(QSPI_MR_SMM, aq->regs + QSPI_MR);
+	atmel_qspi_write(QSPI_MR_SMM, aq, QSPI_MR);
 	aq->mr = QSPI_MR_SMM;
 
 	/* Enable the QSPI controller */
-	writel_relaxed(QSPI_CR_QSPIEN, aq->regs + QSPI_CR);
+	atmel_qspi_write(QSPI_CR_QSPIEN, aq, QSPI_CR);
 }
 
 static irqreturn_t atmel_qspi_interrupt(int irq, void *dev_id)
@@ -437,8 +518,8 @@
 	struct atmel_qspi *aq = dev_id;
 	u32 status, mask, pending;
 
-	status = readl_relaxed(aq->regs + QSPI_SR);
-	mask = readl_relaxed(aq->regs + QSPI_IMR);
+	status = atmel_qspi_read(aq, QSPI_SR);
+	mask = atmel_qspi_read(aq, QSPI_IMR);
 	pending = status & mask;
 
 	if (!pending)
@@ -568,7 +649,7 @@
 	struct atmel_qspi *aq = spi_controller_get_devdata(ctrl);
 
 	spi_unregister_controller(ctrl);
-	writel_relaxed(QSPI_CR_QSPIDIS, aq->regs + QSPI_CR);
+	atmel_qspi_write(QSPI_CR_QSPIDIS, aq, QSPI_CR);
 	clk_disable_unprepare(aq->qspick);
 	clk_disable_unprepare(aq->pclk);
 	return 0;
@@ -595,7 +676,7 @@
 
 	atmel_qspi_init(aq);
 
-	writel_relaxed(aq->scr, aq->regs + QSPI_SCR);
+	atmel_qspi_write(aq->scr, aq, QSPI_SCR);
 
 	return 0;
 }