Re: [PATCH] i2c-designware: add i2c gpio recovery option

[Phil Reid]

On 11/05/2017 21:53, Andy Shevchenko wrote:
> > > > +static int i2c_dw_init_recovery_info(struct dw_i2c_dev *dev,
> > > > +                                    struct i2c_adapter *adap)
> > > > +{
> > > > +       struct i2c_bus_recovery_info *rinfo = &dev->rinfo;
> > > > +
> > > > +       dev->gpio_scl = devm_gpiod_get_optional(dev->dev,
> > > > +                                               "scl",
> > > > +                                               GPIOD_OUT_HIGH);
> > > > +       if (IS_ERR_OR_NULL(dev->gpio_scl))
> > > This is wrong. You should not use this macro in most cases. And
> > > especially it breaks the logic behind _optional().
> > My logic here was that if the gpio is optional return null we return
> > 0.
> Why?!
>
> _optional()*implies*  that all rest calls will go fine and do nothing.
>
> > which is an okay status.
> > But this breaks if !CONFIG_GPIOLIB, which I keep forgetting. I've
> > never
> > quite wrapped my head around why that's the case.
> >
> > But the probe function only bails out if this returns EPROBE_DEFER.
> > Not sure that's the best approach
> You need something like
>
> desc = devm_gpiod_get_optional(...);
> if (IS_ERR(desc))
>   return PTR_ERR(desc);
I found that continuing without the check on null results in a kernel panic for a dereferenced null pointer.
So something in the gpiolib doesn't treat a null desc as optional.

It was probably this code:
int desc_to_gpio(const struct gpio_desc *desc)
{
	return desc->gdev->base + (desc - &desc->gdev->descs[0]);
}

So perhaps this should return an invalid gpio number when desc == null

I don't know what the intents are, so don't know if its a "bug" or  by design.

--
Regards
Phil Reid