i2c: Document struct i2c_msg

Clarify use of the I2C_M_* flags by highlighting the fact that
most of them depend on I2C_FUNC_PROTOCOL_MANGLING.

Also provide kerneldoc for i2c_smbus_read_block_data() and also
for "struct i2c_msg".

Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>
Signed-off-by: Jean Delvare <khali@linux-fr.org>

1 files changed, 16 insertions, 1 deletions

diff --git a/drivers/i2c/i2c-core.c b/drivers/i2c/i2c-core.c
index f95b1b657618..5e58b5641a35 100644
--- a/drivers/i2c/i2c-core.c
+++ b/drivers/i2c/i2c-core.c
@@ -1307,7 +1307,22 @@ s32 i2c_smbus_write_word_data(struct i2c_client *client, u8 command, u16 value)
 }
 EXPORT_SYMBOL(i2c_smbus_write_word_data);
 
-/* Returns the number of read bytes */
+/**
+ * i2c_smbus_read_block_data - SMBus block read request
+ * @client: Handle to slave device
+ * @command: Command byte issued to let the slave know what data should
+ *      be returned
+ * @values: Byte array into which data will be read; big enough to hold
+ *      the data returned by the slave.  SMBus allows at most 32 bytes.
+ *
+ * Returns the number of bytes read in the slave's response, else a
+ * negative number to indicate some kind of error.
+ *
+ * Note that using this function requires that the client's adapter support
+ * the I2C_FUNC_SMBUS_READ_BLOCK_DATA functionality.  Not all adapter drivers
+ * support this; its emulation through I2C messaging relies on a specific
+ * mechanism (I2C_M_RECV_LEN) which may not be implemented.
+ */
 s32 i2c_smbus_read_block_data(struct i2c_client *client, u8 command,
                               u8 *values)
 {