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i2c: Document the message size limit

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

Signed-off-by: Zhangfei Gao <zgao6@marvell.com>
Signed-off-by: Jean Delvare <khali@linux-fr.org>
This commit is contained in:
Zhangfei Gao 2010-03-02 12:23:49 +01:00 committed by Jean Delvare
parent eec74a257f
commit 0c43ea544c
3 changed files with 6 additions and 4 deletions
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5
Documentation/i2c/writing-clients
View file

@ -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);

4
drivers/i2c/i2c-core.c
View file

@ -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.
*/

1
include/linux/i2c.h
View file

@ -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);