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>

7 files changed, 23 insertions, 12 deletions

diff --git a/drivers/i2c/busses/i2c-powermac.c b/drivers/i2c/busses/i2c-powermac.c
index 1425d2245c8..0ab4f2627c2 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 7a2bc06304f..a0f7e4a303b 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 dc64f8b6b24..e6c4a2b762e 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;
diff --git a/drivers/i2c/chips/eeprom.c b/drivers/i2c/chips/eeprom.c
index bfce13c8f1f..48f857ae874 100644
--- a/drivers/i2c/chips/eeprom.c
+++ b/drivers/i2c/chips/eeprom.c
@@ -88,8 +88,10 @@ static void eeprom_update_client(struct i2c_client *client, u8 slice)
 		dev_dbg(&client->dev, "Starting eeprom update, slice %u\n", slice);
 
 		if (i2c_check_functionality(client->adapter, I2C_FUNC_SMBUS_READ_I2C_BLOCK)) {
-			for (i = slice << 5; i < (slice + 1) << 5; i += I2C_SMBUS_BLOCK_MAX)
-				if (i2c_smbus_read_i2c_block_data(client, i, data->data + i) != I2C_SMBUS_BLOCK_MAX)
+			for (i = slice << 5; i < (slice + 1) << 5; i += 32)
+				if (i2c_smbus_read_i2c_block_data(client, i,
+							32, data->data + i)
+							!= 32)
 					goto exit;
 		} else {
 			if (i2c_smbus_write_byte(client, slice << 5)) {
diff --git a/drivers/i2c/chips/max6875.c b/drivers/i2c/chips/max6875.c
index 76645c14297..e9e9e5171b5 100644
--- a/drivers/i2c/chips/max6875.c
+++ b/drivers/i2c/chips/max6875.c
@@ -106,6 +106,7 @@ static void max6875_update_slice(struct i2c_client *client, int slice)
 					    I2C_FUNC_SMBUS_READ_I2C_BLOCK)) {
 			if (i2c_smbus_read_i2c_block_data(client,
 							  MAX6875_CMD_BLK_READ,
+							  SLICE_SIZE,
 							  buf) != SLICE_SIZE) {
 				goto exit_up;
 			}
diff --git a/drivers/i2c/i2c-core.c b/drivers/i2c/i2c-core.c
index cccfa867824..6971a62397d 100644
--- a/drivers/i2c/i2c-core.c
+++ b/drivers/i2c/i2c-core.c
@@ -1344,10 +1344,14 @@ s32 i2c_smbus_write_block_data(struct i2c_client *client, u8 command,
 EXPORT_SYMBOL(i2c_smbus_write_block_data);
 
 /* Returns the number of read bytes */
-s32 i2c_smbus_read_i2c_block_data(struct i2c_client *client, u8 command, u8 *values)
+s32 i2c_smbus_read_i2c_block_data(struct i2c_client *client, u8 command,
+				  u8 length, u8 *values)
 {
 	union i2c_smbus_data data;
 
+	if (length > I2C_SMBUS_BLOCK_MAX)
+		length = I2C_SMBUS_BLOCK_MAX;
+	data.block[0] = length;
 	if (i2c_smbus_xfer(client->adapter,client->addr,client->flags,
 	                      I2C_SMBUS_READ,command,
 	                      I2C_SMBUS_I2C_BLOCK_DATA,&data))
@@ -1468,7 +1472,7 @@ static s32 i2c_smbus_xfer_emulated(struct i2c_adapter * adapter, u16 addr,
 		break;
 	case I2C_SMBUS_I2C_BLOCK_DATA:
 		if (read_write == I2C_SMBUS_READ) {
-			msg[1].len = I2C_SMBUS_BLOCK_MAX;
+			msg[1].len = data->block[0];
 		} else {
 			msg[0].len = data->block[0] + 1;
 			if (msg[0].len > I2C_SMBUS_BLOCK_MAX + 1) {
@@ -1524,9 +1528,7 @@ static s32 i2c_smbus_xfer_emulated(struct i2c_adapter * adapter, u16 addr,
 				data->word = msgbuf1[0] | (msgbuf1[1] << 8);
 				break;
 			case I2C_SMBUS_I2C_BLOCK_DATA:
-				/* fixed at 32 for now */
-				data->block[0] = I2C_SMBUS_BLOCK_MAX;
-				for (i = 0; i < I2C_SMBUS_BLOCK_MAX; i++)
+				for (i = 0; i < data->block[0]; i++)
 					data->block[i+1] = msgbuf1[i];
 				break;
 			case I2C_SMBUS_BLOCK_DATA:
diff --git a/drivers/i2c/i2c-dev.c b/drivers/i2c/i2c-dev.c
index e7a70971059..64eee9551b2 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);