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

Lukasz Majewski
2015-02-23T16:51:34Z

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).

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;
}

num = ret;
ctx->pwm_fan_cooling_levels = devm_kzalloc(dev, num *
sizeof(u32), GFP_KERNEL);
if (!ctx->pwm_fan_cooling_levels)
return -ENOMEM;

ret = of_property_read_u32_array(np, "cooling-levels",
ctx->pwm_fan_cooling_levels,
num);
if (ret) {
dev_err(dev, "Property 'cooling-levels' cannot be
read!\n");
return ret;
}

for (i = 0; i < num; i++) {
if (ctx->pwm_fan_cooling_levels[i] > MAX_PWM) {
dev_err(dev, "PWM fan state[%d]:%d > %d\n", i,
ctx->pwm_fan_cooling_levels[i],
MAX_PWM);
return -EINVAL;
}
}

ctx->pwm_fan_max_state = num - 1;

return 0;
}

>
> Guenter

--
Best regards,

Lukasz Majewski

Samsung R&D Institute Poland (SRPOL) | Linux Platform Group