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, 9 insertions, 0 deletions

diff --git a/drivers/i2c/i2c-dev.c b/drivers/i2c/i2c-dev.c
index e7a709710592..64eee9551b22 100644
--- a/drivers/i2c/i2c-dev.c
+++ b/drivers/i2c/i2c-dev.c
@@ -283,6 +283,7 @@ static int i2cdev_ioctl(struct inode *inode, struct file *file,
                     (data_arg.size != I2C_SMBUS_WORD_DATA) &&
                     (data_arg.size != I2C_SMBUS_PROC_CALL) &&
                     (data_arg.size != I2C_SMBUS_BLOCK_DATA) &&
+                    (data_arg.size != I2C_SMBUS_I2C_BLOCK_BROKEN) &&
                     (data_arg.size != I2C_SMBUS_I2C_BLOCK_DATA) &&
                     (data_arg.size != I2C_SMBUS_BLOCK_PROC_CALL)) {
                         dev_dbg(&client->adapter->dev,
@@ -329,10 +330,18 @@ static int i2cdev_ioctl(struct inode *inode, struct file *file,
 
                 if ((data_arg.size == I2C_SMBUS_PROC_CALL) ||
                     (data_arg.size == I2C_SMBUS_BLOCK_PROC_CALL) ||
+                    (data_arg.size == I2C_SMBUS_I2C_BLOCK_DATA) ||
                     (data_arg.read_write == I2C_SMBUS_WRITE)) {
                         if (copy_from_user(&temp, data_arg.data, datasize))
                                 return -EFAULT;
                 }
+                if (data_arg.size == I2C_SMBUS_I2C_BLOCK_BROKEN) {
+                        /* Convert old I2C block commands to the new
+                           convention. This preserves binary compatibility. */
+                        data_arg.size = I2C_SMBUS_I2C_BLOCK_DATA;
+                        if (data_arg.read_write == I2C_SMBUS_READ)
+                                temp.block[0] = I2C_SMBUS_BLOCK_MAX;
+                }
                 res = i2c_smbus_xfer(client->adapter,client->addr,client->flags,
                       data_arg.read_write,
                       data_arg.command,data_arg.size,&temp);