Hi Krzysztof:
* Krzysztof Halasa <[email protected]> [2006-06-06 18:58:46 +0200]:
> Another thing: I noticed the i2c_bit_add_bus doesn't set SDA and SCL
> lines to a known levels. If the hw driver set them to 1 all is fine
> and the first START condition is detected correctly. But if they're
> set differently (for example, if both are zero), the START will not
> work.
>
> I'm not sure if the following patch isn't an overkill, though, and
> if the lack of initialization is a real problem which shows in
> practice and not only on my analyzer.
>
> In case you think it's needed:
>
> This patch makes i2c_bit_add_bus() initialize SDA and SCL lines
> as required by subsequent START condition.
>
> Signed-off-by: Krzysztof Halasa <[email protected]>
>
> --- a/drivers/i2c/algos/i2c-algo-bit.c
> +++ b/drivers/i2c/algos/i2c-algo-bit.c
> @@ -544,6 +544,13 @@ int i2c_bit_add_bus(struct i2c_adapter *
> adap->timeout = 100; /* default values, should */
> adap->retries = 3; /* be replaced by defines */
>
> + setsda(bit_adap, 0); /* may mean START if SCL = 1 */
> + udelay(bit_adap->udelay);
> + setscl(bit_adap, 1); /* may clock a zero bit in */
> + udelay(bit_adap->udelay);
> + setsda(bit_adap, 1); /* STOP */
> + udelay(bit_adap->udelay);
> +
> i2c_add_adapter(adap);
> return 0;
> }
NACK. The I2C bus spec says[1]:
A START condition immediately followed by a STOP condition
(void message) is an illegal format.
SCL and SDA must be pulled high by hardware. If a driver inits to
setting them low, that's a bug in the driver.
[1] (page 14, note 5)
http://www.semiconductors.philips.com/acrobat_download/literature/9398/39340011.pdf
Regards,
--
Mark M. Hoffman
[email protected]
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