Re: [PATCH 2/5] em28xx: respect the message size constraints for i2c transfers

[Antti Palosaari <crope@iki.fi>]

On 12/14/2012 06:28 PM, Frank Schäfer wrote:
> The em2800 can transfer up to 4 bytes per i2c message.
> All other em25xx/em27xx/28xx chips can transfer at least 64 bytes per message.
>
> I2C adapters should never split messages transferred via the I2C subsystem
> into multiple message transfers, because the result will almost always NOT be
> the same as when the whole data is transferred to the I2C client in a single
> message.
> If the message size exceeds the capabilities of the I2C adapter, -EOPNOTSUPP
> should be returned.
>
> Signed-off-by: Frank Schäfer <fschaefer.oss@googlemail.com>


> +	if (len < 1 || len > 4)
> +		return -EOPNOTSUPP;

That patch seem to be good for my eyes, but that check for len < 1 is 
something I would like to double checked. Generally len = 0 is OK and is 
used some cases, probing and sometimes when all registers are read for 
example.

Did you test it returns some error for zero len messages?

regards
Antti

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