Re: [PATCH 1/2] i2c: add "reset" sysfs entry for adapters.

[Jean Delvare <khali-PUYAD+kWke1g9hUCZPvPmw@public.gmane.org>]

On Fri,  6 Feb 2009 16:23:17 +0100, Rodolfo Giometti wrote:
> It could happen that an i2c adapter may lock the bus due due

Typo: "due due" -> "due to".

> electrical problems, so the user may recover this stale state by using:
> 
> 	$ echo 1 > /sys/class/i2c-adapter/i2c-0/reset

What is the intended purpose, debugging? I would certainly hope that
drivers know by themselves when they need a reset. Requiring users to
reset themselves doesn't sound terribly friendly :(

> Signed-off-by: Rodolfo Giometti <giometti-k2GhghHVRtY@public.gmane.org>
> ---
>  drivers/i2c/i2c-core.c |   21 +++++++++++++++++++++
>  include/linux/i2c.h    |    2 ++
>  2 files changed, 23 insertions(+), 0 deletions(-)
> 
> diff --git a/drivers/i2c/i2c-core.c b/drivers/i2c/i2c-core.c
> index b1c9abe..b0c4053 100644
> --- a/drivers/i2c/i2c-core.c
> +++ b/drivers/i2c/i2c-core.c
> @@ -393,8 +393,29 @@ show_adapter_name(struct device *dev, struct device_attribute *attr, char *buf)
>  	return sprintf(buf, "%s\n", adap->name);
>  }
>  
> +static ssize_t
> +write_adapter_reset(struct device *dev, struct device_attribute *attr,
> +				const char *buf, size_t count)
> +{
> +	struct i2c_adapter *adap = to_i2c_adapter(dev);
> +	unsigned long val;
> +	int ret;
> +
> +	if (!adap->reset)
> +		return -EINVAL;
> +
> +	ret = strict_strtoul(buf, 10, &val);
> +	if (ret || val != 1)
> +		return -EINVAL;
> +
> +	adap->reset(adap);

I consider it good practice to always test for function pointers
_right_ before dereferencing them. Makes it harder to accidentally
break things later.

> +
> +	return count;
> +}
> +
>  static struct device_attribute i2c_adapter_attrs[] = {
>  	__ATTR(name, S_IRUGO, show_adapter_name, NULL),
> +	__ATTR(reset, S_IWUSR, NULL, write_adapter_reset),
>  	{ },
>  };
>  
> diff --git a/include/linux/i2c.h b/include/linux/i2c.h
> index fcfbfea..0f84345 100644
> --- a/include/linux/i2c.h
> +++ b/include/linux/i2c.h
> @@ -369,6 +369,8 @@ struct i2c_adapter {
>  	struct list_head clients;	/* DEPRECATED */
>  	char name[48];
>  	struct completion dev_released;
> +
> +	void (*reset)(struct i2c_adapter *);	/* user request adap reset */
>  };
>  #define to_i2c_adapter(d) container_of(d, struct i2c_adapter, dev)
>  


-- 
Jean Delvare