[U-Boot] [PATCH] 2c: modify i2c_read API to handle multi-bytes writes

[York Sun <yorksun@freescale.com>]

On 04/04/2014 03:08 AM, Shaveta Leekha wrote:
> Most of the I2C slaves support accesses in the typical style
> viz.read/write series of bytes at particular address offset.

viz?


> These transactions are currently supportd in the
> i2c driver using i2c_read and i2c_write APIs. I2C EEPROMs,
> RTC, etc fall in this category.
> The transactions look like:"
> START:Address:Tx:Offset:RESTART:Address[0..4]:Tx/Rx:data[0..n]:STOP"
> 
> However there are certain devices which support accesses in
> terms of the transactions as follows:
> "START:Address:Tx:Txdata[0..n1]:Clock_stretching:
>         RESTART:Address:Rx:data[0..n2]"
> 
> The Txdata is typically a command and some associated data,
> similarly Rxdata could be command status plus some data received
> as a response to the command sent.
> i2c_read() function has been modified to handle
> both types of transactions:
> the one that writes only offset/address before read and other that
> writes some bytes(more than 4 bytes) before read

Please rephrase this sentence. It is not very clear.


> 
> To handle the case:
> Negative equivalent of length has been passed and
> interpreted accordinglt and txdata is being passed in
> rxdata buffer

This belongs to inline comments. You should explain more in detail in the
comment. Commit message helps but it is hard to find in long term.


> 
> Signed-off-by: Shaveta Leekha <shaveta@freescale.com>
> Signed-off-by: Poonam Aggrwal <poonam.aggrwal@freescale.com>
> ---
>  drivers/i2c/fsl_i2c.c |   40 +++++++++++++++++++++++++++++++---------
>  1 files changed, 31 insertions(+), 9 deletions(-)
> 
> diff --git a/drivers/i2c/fsl_i2c.c b/drivers/i2c/fsl_i2c.c
> index 291ad94..14c66d0 100644
> --- a/drivers/i2c/fsl_i2c.c
> +++ b/drivers/i2c/fsl_i2c.c
> @@ -424,17 +424,39 @@ fsl_i2c_read(struct i2c_adapter *adap, u8 dev, uint addr, int alen, u8 *data,
>  	int i = -1; /* signal error */
>  	u8 *a = (u8*)&addr;
>  
> -	if (i2c_wait4bus(adap) < 0)
> -		return -1;

You don't need to move these two lines.


> +	if (alen < 0) {

You need to put a lot of comment to explain here.

> +		int len = alen * -1;

You don't really need a new variable here. Even you do, put the variable
declaration to the beginning of the function.

> +		if (i2c_wait4bus(adap) < 0)
> +			return -1;
> +
> +		/* Generate a START and send the Address and
> +		 * the Tx Bytes to the slave.
> +		 * "START: Address: Write bytes wdata[wlength]"
> +		 * It supports writing any number of bytes in contrast
> +		 * to the else part, which supports writing address offset
> +		 * of upto 4 bytes only.
> +		 */
> +		if (i2c_write_addr(adap, dev, I2C_WRITE_BIT, 0) != 0)
> +			i = __i2c_write(adap, data, len);

And explain how you use "data".

York