i2c: i801: Don't silently correct invalid transfer size

If an invalid block size is provided, reject it instead of silently
changing it to a supported value. Especially critical I see the case of
a write transfer with block length 0. In this case we have no guarantee
that the byte we would write is valid. When silently reducing a read to
32 bytes then we don't return an error and the caller may falsely
assume that we returned the full requested data.

If this change should break any (broken) caller, then I think we should
fix the caller.

Signed-off-by: Heiner Kallweit <hkallweit1@gmail.com>
Reviewed-by: Jean Delvare <jdelvare@suse.de>
Signed-off-by: Wolfram Sang <wsa@kernel.org>

diff --git a/drivers/i2c/busses/i2c-i801.c b/drivers/i2c/busses/i2c-i801.c
index 41446f9cc52da96db1084ad06a94c08a91d93374..c87ea470eba98724245b23561c3376adcfcccfb5 100644 (file)
--- a/drivers/i2c/busses/i2c-i801.c
+++ b/drivers/i2c/busses/i2c-i801.c
@@ -775,6 +775,11 @@ static int i801_block_transaction(struct i801_priv *priv, union i2c_smbus_data *
        int result = 0;
        unsigned char hostc;
 
+       if (read_write == I2C_SMBUS_READ && command == I2C_SMBUS_BLOCK_DATA)
+               data->block[0] = I2C_SMBUS_BLOCK_MAX;
+       else if (data->block[0] < 1 || data->block[0] > I2C_SMBUS_BLOCK_MAX)
+               return -EPROTO;
+
        if (command == I2C_SMBUS_I2C_BLOCK_DATA) {
                if (read_write == I2C_SMBUS_WRITE) {
                        /* set I2C_EN bit in configuration register */
@@ -788,16 +793,6 @@ static int i801_block_transaction(struct i801_priv *priv, union i2c_smbus_data *
                }
        }
 
-       if (read_write == I2C_SMBUS_WRITE
-        || command == I2C_SMBUS_I2C_BLOCK_DATA) {
-               if (data->block[0] < 1)
-                       data->block[0] = 1;
-               if (data->block[0] > I2C_SMBUS_BLOCK_MAX)
-                       data->block[0] = I2C_SMBUS_BLOCK_MAX;
-       } else {
-               data->block[0] = 32;    /* max for SMBus block reads */
-       }
-
        /* Experience has shown that the block buffer can only be used for
           SMBus (not I2C) block transactions, even though the datasheet
           doesn't mention this limitation. */