diff --git a/drivers/i2c/busses/i2c-mxs.c b/drivers/i2c/busses/i2c-mxs.c
index 2cb0317..f986ff8 100644
--- a/drivers/i2c/busses/i2c-mxs.c
+++ b/drivers/i2c/busses/i2c-mxs.c
@@ -1,6 +1,7 @@
 /*
  * Freescale MXS I2C bus driver
  *
+ * Copyright (C) 2012-2013 Marek Vasut <marex@denx.de>
  * Copyright (C) 2011-2012 Wolfram Sang, Pengutronix e.K.
  *
  * based on a (non-working) driver which was:
@@ -64,6 +65,7 @@
 #define MXS_I2C_CTRL1_SLAVE_IRQ			0x01
 
 #define MXS_I2C_STAT		(0x50)
+#define MXS_I2C_STAT_GOT_A_NAK			0x10000000
 #define MXS_I2C_STAT_BUS_BUSY			0x00000800
 #define MXS_I2C_STAT_CLK_GEN_BUSY		0x00000400
 
@@ -299,48 +301,11 @@ write_init_pio_fail:
 	return -EINVAL;
 }
 
-static int mxs_i2c_pio_wait_dmareq(struct mxs_i2c_dev *i2c)
+static int mxs_i2c_pio_wait_xfer_end(struct mxs_i2c_dev *i2c)
 {
 	unsigned long timeout = jiffies + msecs_to_jiffies(1000);
 
-	while (!(readl(i2c->regs + MXS_I2C_DEBUG0) &
-		MXS_I2C_DEBUG0_DMAREQ)) {
-		if (time_after(jiffies, timeout))
-			return -ETIMEDOUT;
-		cond_resched();
-	}
-
-	return 0;
-}
-
-static int mxs_i2c_pio_wait_cplt(struct mxs_i2c_dev *i2c, int last)
-{
-	unsigned long timeout = jiffies + msecs_to_jiffies(1000);
-
-	/*
-	 * We do not use interrupts in the PIO mode. Due to the
-	 * maximum transfer length being 8 bytes in PIO mode, the
-	 * overhead of interrupt would be too large and this would
-	 * neglect the gain from using the PIO mode.
-	 */
-
-	while (!(readl(i2c->regs + MXS_I2C_CTRL1) &
-		MXS_I2C_CTRL1_DATA_ENGINE_CMPLT_IRQ)) {
-		if (time_after(jiffies, timeout))
-			return -ETIMEDOUT;
-		cond_resched();
-	}
-
-	writel(MXS_I2C_CTRL1_DATA_ENGINE_CMPLT_IRQ,
-		i2c->regs + MXS_I2C_CTRL1_CLR);
-
-	/*
-	 * When ending a transfer with a stop, we have to wait for the bus to
-	 * go idle before we report the transfer as completed. Otherwise the
-	 * start of the next transfer may race with the end of the current one.
-	 */
-	while (last && (readl(i2c->regs + MXS_I2C_STAT) &
-			(MXS_I2C_STAT_BUS_BUSY | MXS_I2C_STAT_CLK_GEN_BUSY))) {
+	while (readl(i2c->regs + MXS_I2C_CTRL0) & MXS_I2C_CTRL0_RUN) {
 		if (time_after(jiffies, timeout))
 			return -ETIMEDOUT;
 		cond_resched();
@@ -378,106 +343,207 @@ static void mxs_i2c_pio_trigger_cmd(struct mxs_i2c_dev *i2c, u32 cmd)
 	writel(reg, i2c->regs + MXS_I2C_CTRL0);
 }
 
+/*
+ * Start WRITE transaction on the I2C bus. By studying i.MX23 datasheet,
+ * CTRL0::PIO_MODE bit description clarifies the order in which the registers
+ * must be written during PIO mode operation. First, the CTRL0 register has
+ * to be programmed with all the necessary bits but the RUN bit. Then the
+ * payload has to be written into the DATA register. Finally, the transmission
+ * is executed by setting the RUN bit in CTRL0.
+ */
+static void mxs_i2c_pio_trigger_write_cmd(struct mxs_i2c_dev *i2c, u32 cmd,
+					  u32 data)
+{
+	writel(cmd, i2c->regs + MXS_I2C_CTRL0);
+	writel(data, i2c->regs + MXS_I2C_DATA);
+	writel(MXS_I2C_CTRL0_RUN, i2c->regs + MXS_I2C_CTRL0_SET);
+}
+
 static int mxs_i2c_pio_setup_xfer(struct i2c_adapter *adap,
 			struct i2c_msg *msg, uint32_t flags)
 {
 	struct mxs_i2c_dev *i2c = i2c_get_adapdata(adap);
 	uint32_t addr_data = msg->addr << 1;
 	uint32_t data = 0;
-	int i, shifts_left, ret;
+	int i, ret, xlen = 0, xmit = 0;
+	uint32_t start;
 
 	/* Mute IRQs coming from this block. */
 	writel(MXS_I2C_IRQ_MASK << 8, i2c->regs + MXS_I2C_CTRL1_CLR);
 
+	/*
+	 * MX23 idea:
+	 * - Enable CTRL0::PIO_MODE (1 << 24)
+	 * - Enable CTRL1::ACK_MODE (1 << 27)
+	 *
+	 * WARNING! The MX23 is broken in some way, even if it claims
+	 * to support PIO, when we try to transfer any amount of data
+	 * that is not aligned to 4 bytes, the DMA engine will have
+	 * bits in DEBUG1::DMA_BYTES_ENABLES still set even after the
+	 * transfer. This in turn will mess up the next transfer as
+	 * the block it emit one byte write onto the bus terminated
+	 * with a NAK+STOP. A possible workaround is to reset the IP
+	 * block after every PIO transmission, which might just work.
+	 *
+	 * NOTE: The CTRL0::PIO_MODE description is important, since
+	 * it outlines how the PIO mode is really supposed to work.
+	 */
+
 	if (msg->flags & I2C_M_RD) {
+		/*
+		 * PIO READ transfer:
+		 *
+		 * This transfer MUST be limited to 4 bytes maximum. It is not
+		 * possible to transfer more than four bytes via PIO, since we
+		 * can not in any way make sure we can read the data from the
+		 * DATA register fast enough. Besides, the RX FIFO is only four
+		 * bytes deep, thus we can only really read up to four bytes at
+		 * time. Finally, there is no bit indicating us that new data
+		 * arrived at the FIFO and can thus be fetched from the DATA
+		 * register.
+		 */
+		BUG_ON(msg->len > 4);
+
 		addr_data |= I2C_SMBUS_READ;
 
 		/* SELECT command. */
-		mxs_i2c_pio_trigger_cmd(i2c, MXS_CMD_I2C_SELECT);
+		mxs_i2c_pio_trigger_write_cmd(i2c, MXS_CMD_I2C_SELECT, addr_data);
 
-		ret = mxs_i2c_pio_wait_dmareq(i2c);
-		if (ret)
-			return ret;
-
-		writel(addr_data, i2c->regs + MXS_I2C_DATA);
-		writel(MXS_I2C_DEBUG0_DMAREQ, i2c->regs + MXS_I2C_DEBUG0_CLR);
-
-		ret = mxs_i2c_pio_wait_cplt(i2c, 0);
-		if (ret)
-			return ret;
-
-		if (mxs_i2c_pio_check_error_state(i2c))
+		ret = mxs_i2c_pio_wait_xfer_end(i2c);
+		if (ret) {
+			dev_err(i2c->dev,
+				"PIO: Failed to send SELECT command!\n");
 			goto cleanup;
+		}
 
 		/* READ command. */
 		mxs_i2c_pio_trigger_cmd(i2c,
 					MXS_CMD_I2C_READ | flags |
 					MXS_I2C_CTRL0_XFER_COUNT(msg->len));
 
+		ret = mxs_i2c_pio_wait_xfer_end(i2c);
+		if (ret) {
+			dev_err(i2c->dev,
+				"PIO: Failed to send SELECT command!\n");
+			goto cleanup;
+		}
+
+		data = readl(i2c->regs + MXS_I2C_DATA);
 		for (i = 0; i < msg->len; i++) {
-			if ((i & 3) == 0) {
-				ret = mxs_i2c_pio_wait_dmareq(i2c);
-				if (ret)
-					return ret;
-				data = readl(i2c->regs + MXS_I2C_DATA);
-				writel(MXS_I2C_DEBUG0_DMAREQ,
-				       i2c->regs + MXS_I2C_DEBUG0_CLR);
-			}
 			msg->buf[i] = data & 0xff;
 			data >>= 8;
 		}
 	} else {
+		/*
+		 * PIO WRITE transfer:
+		 *
+		 * The code below implements clock stretching to circumvent
+		 * the possibility of kernel not being able to supply data
+		 * fast enough. It is possible to transfer arbitrary amount
+		 * of data using PIO write.
+		 */
 		addr_data |= I2C_SMBUS_WRITE;
 
-		/* WRITE command. */
-		mxs_i2c_pio_trigger_cmd(i2c,
-					MXS_CMD_I2C_WRITE | flags |
-					MXS_I2C_CTRL0_XFER_COUNT(msg->len + 1));
-
 		/*
 		 * The LSB of data buffer is the first byte blasted across
 		 * the bus. Higher order bytes follow. Thus the following
 		 * filling schematic.
 		 */
+
 		data = addr_data << 24;
+
+		/* Start the transfer with START condition. */
+		start = MXS_I2C_CTRL0_PRE_SEND_START;
+
+		/* If the transfer is long, use clock stretching. */
+		if (msg->len > 3)
+			start |= MXS_I2C_CTRL0_RETAIN_CLOCK;
+
 		for (i = 0; i < msg->len; i++) {
 			data >>= 8;
 			data |= (msg->buf[i] << 24);
-			if ((i & 3) == 2) {
-				ret = mxs_i2c_pio_wait_dmareq(i2c);
-				if (ret)
-					return ret;
-				writel(data, i2c->regs + MXS_I2C_DATA);
-				writel(MXS_I2C_DEBUG0_DMAREQ,
-				       i2c->regs + MXS_I2C_DEBUG0_CLR);
+
+			xmit = 0;
+
+			/* This is the last transfer of the message. */
+			if (i + 1 == msg->len) {
+				/* Add optional STOP flag. */
+				start |= flags;
+				/* Remove RETAIN_CLOCK bit. */
+				start &= ~MXS_I2C_CTRL0_RETAIN_CLOCK;
+				xmit = 1;
 			}
-		}
 
-		shifts_left = 24 - (i & 3) * 8;
-		if (shifts_left) {
-			data >>= shifts_left;
-			ret = mxs_i2c_pio_wait_dmareq(i2c);
-			if (ret)
-				return ret;
-			writel(data, i2c->regs + MXS_I2C_DATA);
+			/* Four bytes are ready in the "data" variable. */
+			if ((i & 3) == 2)
+				xmit = 1;
+
+			/* Nothing interesting happened, continue stuffing. */
+			if (!xmit)
+				continue;
+
+			/*
+			 * Compute the size of the transfer and shift the
+			 * data accordingly.
+			 *
+			 * i = (4k + 0) .... xlen = 2
+			 * i = (4k + 1) .... xlen = 3
+			 * i = (4k + 2) .... xlen = 4
+			 * i = (4k + 3) .... xlen = 1
+			 */
+
+			if ((i % 4) == 3)
+				xlen = 1;
+			else
+				xlen = (i % 4) + 2;
+
+			data >>= (4 - xlen) * 8;
+
+			dev_dbg(i2c->dev,
+				"PIO: len=%i pos=%i total=%i [W%s%s%s]\n",
+				xlen, i, msg->len,
+				start & MXS_I2C_CTRL0_PRE_SEND_START ? "S": "",
+				start & MXS_I2C_CTRL0_POST_SEND_STOP ? "E": "",
+				start & MXS_I2C_CTRL0_RETAIN_CLOCK ? "C": "");
+
 			writel(MXS_I2C_DEBUG0_DMAREQ,
 			       i2c->regs + MXS_I2C_DEBUG0_CLR);
+
+			mxs_i2c_pio_trigger_write_cmd(i2c,
+				start | MXS_I2C_CTRL0_MASTER_MODE |
+				MXS_I2C_CTRL0_DIRECTION |
+				MXS_I2C_CTRL0_XFER_COUNT(xlen), data);
+
+			/* The START condition is sent only once. */
+			start &= ~MXS_I2C_CTRL0_PRE_SEND_START;
+
+			/* Wait for the end of the transfer. */
+			ret = mxs_i2c_pio_wait_xfer_end(i2c);
+			if (ret) {
+				dev_err(i2c->dev,
+					"PIO: Failed to finish WRITE cmd!\n");
+				break;
+			}
+
+			/* Check NAK here. */
+			ret = readl(i2c->regs + MXS_I2C_STAT) &
+				    MXS_I2C_STAT_GOT_A_NAK;
+			if (ret) {
+				ret = -ENXIO;
+				goto cleanup;
+			}
 		}
 	}
 
-	ret = mxs_i2c_pio_wait_cplt(i2c, flags & MXS_I2C_CTRL0_POST_SEND_STOP);
-	if (ret)
-		return ret;
-
 	/* make sure we capture any occurred error into cmd_err */
-	mxs_i2c_pio_check_error_state(i2c);
+	ret = mxs_i2c_pio_check_error_state(i2c);
 
 cleanup:
 	/* Clear any dangling IRQs and re-enable interrupts. */
 	writel(MXS_I2C_IRQ_MASK, i2c->regs + MXS_I2C_CTRL1_CLR);
 	writel(MXS_I2C_IRQ_MASK << 8, i2c->regs + MXS_I2C_CTRL1_SET);
 
-	return 0;
+	return ret;
 }
 
 /*
@@ -489,6 +555,7 @@ static int mxs_i2c_xfer_msg(struct i2c_adapter *adap, struct i2c_msg *msg,
 	struct mxs_i2c_dev *i2c = i2c_get_adapdata(adap);
 	int ret, err;
 	int flags;
+	int use_pio = 0;
 
 	flags = stop ? MXS_I2C_CTRL0_POST_SEND_STOP : 0;
 
@@ -499,20 +566,25 @@ static int mxs_i2c_xfer_msg(struct i2c_adapter *adap, struct i2c_msg *msg,
 		return -EINVAL;
 
 	/*
-	 * The current boundary to select between PIO/DMA transfer method
-	 * is set to 8 bytes, transfers shorter than 8 bytes are transfered
-	 * using PIO mode while longer transfers use DMA. The 8 byte border is
-	 * based on this empirical measurement and a lot of previous frobbing.
-	 * Note: this special feature only works on i.MX28 SoC
+	 * The MX28 I2C IP block can only do PIO READ for transfer of to up
+	 * 4 bytes of length. The write transfer is not limited as it can use
+	 * clock stretching to avoid FIFO underruns.
 	 */
+	if ((msg->flags & I2C_M_RD) && (msg->len <= 4))
+		use_pio = 1;
+	if (!(msg->flags & I2C_M_RD) && (msg->len < 7))
+		use_pio = 1;
+
+	/* Disable PIO on MX23. */
+	if (i2c->dev_type == MXS_I2C_V1)
+		use_pio = 0;
+
 	i2c->cmd_err = 0;
-	if (0) {	/* disable PIO mode until a proper fix is made */
+	if (use_pio) {
 		ret = mxs_i2c_pio_setup_xfer(adap, msg, flags);
-		if (ret) {
-			err = mxs_i2c_reset(i2c);
-			if (err)
-				return err;
-		}
+		/* No need to reset the block if NAK was received. */
+		if (ret && (ret != -ENXIO))
+			mxs_i2c_reset(i2c);
 	} else {
 		INIT_COMPLETION(i2c->cmd_complete);
 		ret = mxs_i2c_dma_setup_xfer(adap, msg, flags);
@@ -523,9 +595,11 @@ static int mxs_i2c_xfer_msg(struct i2c_adapter *adap, struct i2c_msg *msg,
 						msecs_to_jiffies(1000));
 		if (ret == 0)
 			goto timeout;
+
+		ret = i2c->cmd_err;
 	}
 
-	if (i2c->cmd_err == -ENXIO) {
+	if (ret == -ENXIO) {
 		/*
 		 * If the transfer fails with a NAK from the slave the
 		 * controller halts until it gets told to return to idle state.
@@ -534,8 +608,6 @@ static int mxs_i2c_xfer_msg(struct i2c_adapter *adap, struct i2c_msg *msg,
 		       i2c->regs + MXS_I2C_CTRL1_SET);
 	}
 
-	ret = i2c->cmd_err;
-
 	dev_dbg(i2c->dev, "Done with err=%d\n", ret);
 
 	return ret;
@@ -823,6 +895,7 @@ static void __exit mxs_i2c_exit(void)
 }
 module_exit(mxs_i2c_exit);
 
+MODULE_AUTHOR("Marek Vasut <marex@denx.de>");
 MODULE_AUTHOR("Wolfram Sang <w.sang@pengutronix.de>");
 MODULE_DESCRIPTION("MXS I2C Bus Driver");
 MODULE_LICENSE("GPL");
