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, 4 insertions, 24 deletions

diff --git a/drivers/macintosh/windfarm_smu_sat.c b/drivers/macintosh/windfarm_smu_sat.c
index 1043b39..351982b 100644
--- a/drivers/macintosh/windfarm_smu_sat.c
+++ b/drivers/macintosh/windfarm_smu_sat.c
@@ -67,26 +67,6 @@ static struct i2c_driver wf_sat_driver = {
 	.detach_client	= wf_sat_detach,
 };
 
-/*
- * XXX i2c_smbus_read_i2c_block_data doesn't pass the requested
- * length down to the low-level driver, so we use this, which
- * works well enough with the SMU i2c driver code...
- */
-static int sat_read_block(struct i2c_client *client, u8 command,
-			  u8 *values, int len)
-{
-	union i2c_smbus_data data;
-	int err;
-
-	data.block[0] = len;
-	err = i2c_smbus_xfer(client->adapter, client->addr, client->flags,
-			     I2C_SMBUS_READ, command, I2C_SMBUS_I2C_BLOCK_DATA,
-			     &data);
-	if (!err)
-		memcpy(values, data.block, len);
-	return err;
-}
-
 struct smu_sdbp_header *smu_sat_get_sdb_partition(unsigned int sat_id, int id,
 						  unsigned int *size)
 {
@@ -124,8 +104,8 @@ struct smu_sdbp_header *smu_sat_get_sdb_partition(unsigned int sat_id, int id,
 		return NULL;
 
 	for (i = 0; i < len; i += 4) {
-		err = sat_read_block(&sat->i2c, 0xa, data, 4);
-		if (err) {
+		err = i2c_smbus_read_i2c_block_data(&sat->i2c, 0xa, 4, data);
+		if (err < 0) {
 			printk(KERN_ERR "smu_sat_get_sdb_part rd err %d\n",
 			       err);
 			goto fail;
@@ -157,8 +137,8 @@ static int wf_sat_read_cache(struct wf_sat *sat)
 {
 	int err;
 
-	err = sat_read_block(&sat->i2c, 0x3f, sat->cache, 16);
-	if (err)
+	err = i2c_smbus_read_i2c_block_data(&sat->i2c, 0x3f, 16, sat->cache);
+	if (err < 0)
 		return err;
 	sat->last_read = jiffies;
 #ifdef LOTSA_DEBUG