[PATCH 2/4] i2c: xlp9xx: Handle transactions with I2C_M_RECV_LEN properly

[George Cherian]

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.

Signed-off-by: George Cherian <george.cher...@cavium.com>
---
 drivers/i2c/busses/i2c-xlp9xx.c | 31 ++++++++++++++++++++++++-------
 1 file changed, 24 insertions(+), 7 deletions(-)

diff --git a/drivers/i2c/busses/i2c-xlp9xx.c b/drivers/i2c/busses/i2c-xlp9xx.c
index 6d78cdc..b5b224e 100644
--- a/drivers/i2c/busses/i2c-xlp9xx.c
+++ b/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)
-- 
2.1.4