On Thu, Feb 4, 2010 at 9:14 PM, Jean Delvare <khali@xxxxxxxxxxxx> wrote: > On Thu, 4 Feb 2010 04:47:41 -0800, Eric Miao wrote: >> > How about return error in i2c_master_send & i2c_master_recv when count >> > is bigger than 64K, as suggested by Ben. >> >> I think that's more preferable. Making the count parameter as u16, >> though is going to generate a warning, yet that's usually ignored >> by careless programmer, screaming out when this happens might >> be more useful sometimes. > > Developers ignoring warnings get the pain the deserve. > > A check on "count" would come at the price of a small performance hit > for every caller, even though in 99% of the cases the check isn't > needed. > > That being said I don't care too much and will take whatever patch is > sent to me. > > It would be a good idea to add a note about this limit in > Documentation/i2c/writing-clients and/or include/linux/i2c.h. > >> > The device I used could receive 32K one time instead, the firmware >> > download only takes place on-demand in fact. >> > However, it took some time to debug, since no error info come out. >> > Add error msg may notify users, though transfering more than 64K data >> > one time is rarely happen. > > -- > Jean Delvare > Hi, Jean Thanks for your instruction. Here is patch to modify some comments of i2c_master_send & i2c_master_recv, is this OK. Thanks Zhangfei >From 30fbf1ebf1facba3d280c887e2ecfd0499e7b04b Mon Sep 17 00:00:00 2001 From: Zhangfei Gao <zgao6@xxxxxxxxxxx> Date: Sat, 6 Feb 2010 05:38:59 +0800 Subject: [PATCH] i2c: notes of i2c_master_send & i2c_master_recv i2c_master_send & i2c_master_recv not support more than 64bytes transfer, since msg.len is __u16 type Signed-off-by: Zhangfei Gao <zgao6@xxxxxxxxxxx> --- Documentation/i2c/writing-clients | 3 ++- drivers/i2c/i2c-core.c | 4 ++-- include/linux/i2c.h | 1 + 3 files changed, 5 insertions(+), 3 deletions(-) diff --git a/Documentation/i2c/writing-clients b/Documentation/i2c/writing-clients index 7860aaf..929a3c3 100644 --- a/Documentation/i2c/writing-clients +++ b/Documentation/i2c/writing-clients @@ -318,7 +318,8 @@ 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 +to read/write (must be less than the length of the buffer, also should be +less than 64K since msg.len is __u16 type.) Returned is the actual number of bytes read/written. int i2c_transfer(struct i2c_adapter *adap, struct i2c_msg *msg, diff --git a/drivers/i2c/i2c-core.c b/drivers/i2c/i2c-core.c index 8d80fce..9607dcc 100644 --- a/drivers/i2c/i2c-core.c +++ b/drivers/i2c/i2c-core.c @@ -1112,7 +1112,7 @@ 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, should be less than 64K since msg.len is u16 * * Returns negative errno, or else the number of bytes written. */ @@ -1139,7 +1139,7 @@ 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, should be less than 64K since msg.len is u16 * * Returns negative errno, or else the number of bytes read. */ diff --git a/include/linux/i2c.h b/include/linux/i2c.h index 57d41b0..b2dea18 100644 --- a/include/linux/i2c.h +++ b/include/linux/i2c.h @@ -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. + * Parameter count should be less than 64K since msg.len is __u16 */ extern int i2c_master_send(struct i2c_client *client, const char *buf, int count); -- 1.6.0.4
Attachment:
0001-i2c-notes-of-i2c_master_send-i2c_master_recv.patch
Description: Binary data
