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>

3 files changed, 2 insertions, 5 deletions

diff --git a/drivers/i2c/busses/i2c-powermac.c b/drivers/i2c/busses/i2c-powermac.c
index 1425d22..0ab4f26 100644
--- a/drivers/i2c/busses/i2c-powermac.c
+++ b/drivers/i2c/busses/i2c-powermac.c
@@ -121,8 +121,7 @@ static s32 i2c_powermac_smbus_xfer(	struct i2c_adapter*	adap,
 		if (rc)
 			goto bail;
 		rc = pmac_i2c_xfer(bus, addrdir, 1, command,
-				   read ? data->block : &data->block[1],
-				   data->block[0]);
+				   &data->block[1], data->block[0]);
 		break;
 
         default:
diff --git a/drivers/i2c/busses/i2c-viapro.c b/drivers/i2c/busses/i2c-viapro.c
index 7a2bc06..a0f7e4a 100644
--- a/drivers/i2c/busses/i2c-viapro.c
+++ b/drivers/i2c/busses/i2c-viapro.c
@@ -235,7 +235,7 @@ static s32 vt596_access(struct i2c_adapter *adap, u16 addr,
 		if (!(vt596_features & FEATURE_I2CBLOCK))
 			goto exit_unsupported;
 		if (read_write == I2C_SMBUS_READ)
-			outb_p(I2C_SMBUS_BLOCK_MAX, SMBHSTDAT0);
+			outb_p(data->block[0], SMBHSTDAT0);
 		/* Fall through */
 	case I2C_SMBUS_BLOCK_DATA:
 		outb_p(command, SMBHSTCMD);
diff --git a/drivers/i2c/busses/scx200_acb.c b/drivers/i2c/busses/scx200_acb.c
index dc64f8b..e6c4a2b 100644
--- a/drivers/i2c/busses/scx200_acb.c
+++ b/drivers/i2c/busses/scx200_acb.c
@@ -310,8 +310,6 @@ static s32 scx200_acb_smbus_xfer(struct i2c_adapter *adapter,
 		break;
 
 	case I2C_SMBUS_I2C_BLOCK_DATA:
-		if (rw == I2C_SMBUS_READ)
-			data->block[0] = I2C_SMBUS_BLOCK_MAX; /* For now */
 		len = data->block[0];
 		if (len == 0 || len > I2C_SMBUS_BLOCK_MAX)
 			return -EINVAL;