Re: [PATCH 2/2] i2c-algo-bit: Complain about masters which can't read SCL

[Ben Dooks <ben-i2c-elnMNo+KYs3YtjvyW6yDsg@public.gmane.org>]

On Tue, Dec 07, 2010 at 11:07:05AM +0100, Jean Delvare wrote:
> The I2C specification explicitly describes both SDA and SCL as
> bidirectional lines. An I2C master with a read-only SCL is thus not
> compliant. If a slow slave stretches the clock, errors will happen,
> so the bus can't be considered as reliable.
> 
> Signed-off-by: Jean Delvare <khali-PUYAD+kWke1g9hUCZPvPmw@public.gmane.org>
> ---
>  drivers/i2c/algos/i2c-algo-bit.c |   14 ++++++++++++--
>  1 file changed, 12 insertions(+), 2 deletions(-)
> 
> --- linux-2.6.37-rc5.orig/drivers/i2c/algos/i2c-algo-bit.c	2010-12-07 11:02:38.000000000 +0100
> +++ linux-2.6.37-rc5/drivers/i2c/algos/i2c-algo-bit.c	2010-12-07 11:03:23.000000000 +0100
> @@ -604,9 +604,10 @@ static int __i2c_bit_add_bus(struct i2c_
>  			     int (*add_adapter)(struct i2c_adapter *))
>  {
>  	struct i2c_algo_bit_data *bit_adap = adap->algo_data;
> +	int ret;
>  
>  	if (bit_test) {
> -		int ret = test_bus(bit_adap, adap->name);
> +		ret = test_bus(bit_adap, adap->name);
>  		if (ret < 0)
>  			return -ENODEV;
>  	}
> @@ -615,7 +616,16 @@ static int __i2c_bit_add_bus(struct i2c_
>  	adap->algo = &i2c_bit_algo;
>  	adap->retries = 3;
>  
> -	return add_adapter(adap);
> +	ret = add_adapter(adap);
> +	if (ret < 0)
> +		return ret;
> +
> +	/* Complain if SCL can't be read */
> +	if (bit_adap->getscl == NULL) {
> +		dev_warn(&adap->dev, "Not I2C compliant: can't read SCL\n");

I'll have a think about wording. I might be able to improve it.

As a note, I always prefer cannot to can't. 

> +		dev_warn(&adap->dev, "Bus may be unreliable\n");

if there are any other warnings, should we print just one unreliable warning
at the end of the scan?

-- 
Ben

Q:      What's a light-year?
A:      One-third less calories than a regular year.