i2c: xlp9xx: Handle transactions with I2C_M_RECV_LEN properly

In case of transaction with I2C_M_RECV_LEN set, make sure the driver reads
the first byte and then updates the RX fifo with the expected length. Set
threshold to 1 byte so that driver gets an interrupt on receiving the first byte.
After which the transfer length is updated depending on the received length.
Also report SMBus block read functionality.

Signed-off-by: George Cherian <george.cherian@cavium.com>
Tested-by: dann frazier <dann.frazier@canonical.com>
Signed-off-by: Wolfram Sang <wsa@the-dreams.de>

drivers/i2c/busses/i2c-xlp9xx.c

@@ -125,7 +125,16 @@ static void xlp9xx_i2c_update_rx_fifo_thres(struct xlp9xx_i2c_dev *priv)
 {
 	u32 thres;
 
-	thres = min(priv->msg_buf_remaining, XLP9XX_I2C_FIFO_SIZE);
+	if (priv->len_recv)
+		/* interrupt after the first read to examine
+		 * the length byte before proceeding further
+		 */
+		thres = 1;
+	else if (priv->msg_buf_remaining > XLP9XX_I2C_FIFO_SIZE)
+		thres = XLP9XX_I2C_FIFO_SIZE;
+	else
+		thres = priv->msg_buf_remaining;
+
 	xlp9xx_write_i2c_reg(priv, XLP9XX_I2C_MFIFOCTRL,
 			     thres << XLP9XX_I2C_MFIFOCTRL_HITH_SHIFT);
 }
@@ -144,7 +153,7 @@ static void xlp9xx_i2c_fill_tx_fifo(struct xlp9xx_i2c_dev *priv)
 
 static void xlp9xx_i2c_drain_rx_fifo(struct xlp9xx_i2c_dev *priv)
 {
-	u32 len, i;
+	u32 len, i, val;
 	u8 rlen, *buf = priv->msg_buf;
 
 	len = xlp9xx_read_i2c_reg(priv, XLP9XX_I2C_FIFOWCNT) &
@@ -156,19 +165,27 @@ static void xlp9xx_i2c_drain_rx_fifo(struct xlp9xx_i2c_dev *priv)
 		rlen = xlp9xx_read_i2c_reg(priv, XLP9XX_I2C_MRXFIFO);
 		*buf++ = rlen;
 		len--;
+
 		if (priv->client_pec)
 			++rlen;
 		/* update remaining bytes and message length */
 		priv->msg_buf_remaining = rlen;
 		priv->msg_len = rlen + 1;
 		priv->len_recv = false;
-	}
 
-	len = min(priv->msg_buf_remaining, len);
-	for (i = 0; i < len; i++, buf++)
-		*buf = xlp9xx_read_i2c_reg(priv, XLP9XX_I2C_MRXFIFO);
+		/* Update transfer length to read only actual data */
+		val = xlp9xx_read_i2c_reg(priv, XLP9XX_I2C_CTRL);
+		val = (val & ~XLP9XX_I2C_CTRL_MCTLEN_MASK) |
+			((rlen + 1) << XLP9XX_I2C_CTRL_MCTLEN_SHIFT);
+		xlp9xx_write_i2c_reg(priv, XLP9XX_I2C_CTRL, val);
+	} else {
+		len = min(priv->msg_buf_remaining, len);
+		for (i = 0; i < len; i++, buf++)
+			*buf = xlp9xx_read_i2c_reg(priv, XLP9XX_I2C_MRXFIFO);
+
+		priv->msg_buf_remaining -= len;
+	}
 
-	priv->msg_buf_remaining -= len;
 	priv->msg_buf = buf;
 
 	if (priv->msg_buf_remaining)
@@ -357,8 +374,8 @@ static int xlp9xx_i2c_xfer(struct i2c_adapter *adap, struct i2c_msg *msgs,
 
 static u32 xlp9xx_i2c_functionality(struct i2c_adapter *adapter)
 {
-	return I2C_FUNC_SMBUS_EMUL | I2C_FUNC_I2C |
-		I2C_FUNC_10BIT_ADDR;
+	return I2C_FUNC_SMBUS_EMUL | I2C_FUNC_SMBUS_READ_BLOCK_DATA |
+			I2C_FUNC_I2C | I2C_FUNC_10BIT_ADDR;
 }
 
 static const struct i2c_algorithm xlp9xx_i2c_algo = {