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

[Rodolfo Giometti <giometti-AVVDYK/kqiJWk0Htik3J/w@public.gmane.org>]

On Mon, Feb 09, 2009 at 05:17:20PM +0100, Jean Delvare wrote:
> 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".

Ok.

> > 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 :(

Unluckely not all adapter does it by themselfes! At least not PXA
one. I'm currently work on adding this new feature.

> > 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.

Ok.

> > +
> > +	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)
> >  

I'll repropose a new patch ASAP.

Ciao,

Rodolfo

-- 

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Linux Device Driver                          giometti-k2GhghHVRtY@public.gmane.org
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