Re: [PATCH v4 7/8] hwmon: pwm-fan: Read PWM FAN configuration from device tree

Guenter Roeck
2015-02-23T17:01:04Z

On Mon, Feb 23, 2015 at 05:51:22PM +0100, Lukasz Majewski wrote:
> Hi Guenter,
>
> > On Mon, Feb 23, 2015 at 05:13:36PM +0100, Lukasz Majewski wrote:
> > > Hi Guenter,
> > >
> > [ ... ]
> >
> > > >
> > > > If devicetree is not configured, of_property_count_elems_of_size
> > > > returns -ENOSYS, which is returned, causing the driver to fail
> > > > loading.
> > >
> > > Has of_property_count_elems_of_size() returns -ENOSYS?
> > >
> > > Maybe something has changed, but in my linux-vanila (3.19-rc4)
> > > at ./drivers/of/base.c it returns -EINVAL, -ENODATA or number of
> > > elements.
> > >
> > > Have I missed something?
> > >
> > Hi Lukasz,
> >
> > Yes, you have. Check include/linux/of.h, line 484, in latest mainline.
>
> Ok. Now I got it.
>
> The above situation shouldn't happen if I put of_find_property() check
> on the very beginning of this function (it returns NULL when DT support
> is not compiled).
>

Correct.

> The function would look as follows:
>
> int
> pwm_fan_of_get_cooling_data(struct device *dev, struct pwm_fan_ctx
> *ctx)
> {
> struct device_node *np = dev->of_node;
> int num, i, ret;
>
> if (!of_find_property(np, "cooling-levels", NULL))
> return 0;
>
> ret = of_property_count_u32_elems(np, "cooling-levels");
> if (ret <= 0) {
> dev_err(dev, "Wrong data!\n");
> return ret;

This should probably be something like

return ret ? : -EINVAL;

or ret == 0 is not an error, and you should not display an error message
in that case.

Thanks,
Guenter