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Commit 0c43ea54 authored by Zhangfei Gao's avatar Zhangfei Gao Committed by Jean Delvare
Browse files

i2c: Document the message size limit 



i2c_master_send & i2c_master_recv do not support more than 64 kb
transfer, since msg.len is u16.

Signed-off-by: default avatarZhangfei Gao <zgao6@marvell.com>
Signed-off-by: default avatarJean Delvare <khali@linux-fr.org>
parent eec74a25

Documentation/i2c/writing-clients

+3 −2
Original line number Diff line number Diff line
@@ -318,8 +318,9 @@ Plain I2C communication 
These routines read and write some bytes from/to a client. The client

contains the i2c address, so you do not have to include it. The second

parameter contains the bytes to read/write, the third the number of bytes

to read/write (must be less than the length of the buffer.) Returned is

the actual number of bytes read/written.

to read/write (must be less than the length of the buffer, also should be

less than 64k since msg.len is u16.) Returned is the actual number of bytes

read/written.



	int i2c_transfer(struct i2c_adapter *adap, struct i2c_msg *msg,

			 int num);

drivers/i2c/i2c-core.c

+2 −2
Original line number Diff line number Diff line
@@ -1183,7 +1183,7 @@ EXPORT_SYMBOL(i2c_transfer); 
 * i2c_master_send - issue a single I2C message in master transmit mode

 * @client: Handle to slave device

 * @buf: Data that will be written to the slave

 * @count: How many bytes to write

 * @count: How many bytes to write, must be less than 64k since msg.len is u16

 *

 * Returns negative errno, or else the number of bytes written.

 */
@@ -1210,7 +1210,7 @@ EXPORT_SYMBOL(i2c_master_send); 
 * i2c_master_recv - issue a single I2C message in master receive mode

 * @client: Handle to slave device

 * @buf: Where to store data read from slave

 * @count: How many bytes to read

 * @count: How many bytes to read, must be less than 64k since msg.len is u16

 *

 * Returns negative errno, or else the number of bytes read.

 */

include/linux/i2c.h

+1 −0
Original line number Diff line number Diff line
@@ -53,6 +53,7 @@ struct i2c_board_info; 
 * on a bus (or read from them). Apart from two basic transfer functions to

 * transmit one message at a time, a more complex version can be used to

 * transmit an arbitrary number of messages without interruption.

 * @count must be be less than 64k since msg.len is u16.

 */

extern int i2c_master_send(struct i2c_client *client, const char *buf,

			   int count);