i2c: Fix the i2c_smbus_read_i2c_block_data() prototype

Let the drivers specify how many bytes they want to read with
i2c_smbus_read_i2c_block_data(). So far, the block count was
hard-coded to I2C_SMBUS_BLOCK_MAX (32), which did not make much sense.
Many driver authors complained about this before, and I believe it's
about time to fix it. Right now, authors have to do technically stupid
things, such as individual byte reads or full-fledged I2C messaging,
to work around the problem. We do not want to encourage that.

I even found that some bus drivers (e.g. i2c-amd8111) already
implemented I2C block read the "right" way, that is, they didn't
follow the old, broken standard. The fact that it was never noticed
before just shows how little i2c_smbus_read_i2c_block_data() was used,
which isn't that surprising given how broken its prototype was so far.

There are some obvious compatiblity considerations:
* This changes the i2c_smbus_read_i2c_block_data() prototype. Users
  outside the kernel tree will notice at compilation time, and will
  have to update their code.
* User-space has access to i2c_smbus_xfer() directly using i2c-dev, so
  the changed expectations would affect tools such as i2cdump. In order
  to preserve binary compatibility, we give I2C_SMBUS_I2C_BLOCK_DATA
  a new numeric value, and define I2C_SMBUS_I2C_BLOCK_BROKEN with the
  old numeric value. When i2c-dev receives a transaction with the
  old value, it can convert it to the new format on the fly.

Signed-off-by: Jean Delvare <khali@linux-fr.org>

1 files changed, 3 insertions, 2 deletions

diff --git a/include/linux/i2c.h b/include/linux/i2c.h
index 44f2ecf47d9f..2eaba21b9b1a 100644
--- a/include/linux/i2c.h
+++ b/include/linux/i2c.h
@@ -90,7 +90,7 @@ extern s32 i2c_smbus_write_block_data(struct i2c_client * client,
                                       const u8 *values);
 /* Returns the number of read bytes */
 extern s32 i2c_smbus_read_i2c_block_data(struct i2c_client * client,
-                                         u8 command, u8 *values);
+                                         u8 command, u8 length, u8 *values);
 extern s32 i2c_smbus_write_i2c_block_data(struct i2c_client * client,
                                           u8 command, u8 length,
                                           const u8 *values);
@@ -524,8 +524,9 @@ union i2c_smbus_data {
 #define I2C_SMBUS_WORD_DATA         3
 #define I2C_SMBUS_PROC_CALL         4
 #define I2C_SMBUS_BLOCK_DATA        5
-#define I2C_SMBUS_I2C_BLOCK_DATA    6
+#define I2C_SMBUS_I2C_BLOCK_BROKEN  6
 #define I2C_SMBUS_BLOCK_PROC_CALL   7           /* SMBus 2.0 */
+#define I2C_SMBUS_I2C_BLOCK_DATA    8
 
 
 /* ----- commands for the ioctl like i2c_command call: