From mboxrd@z Thu Jan  1 00:00:00 1970
From: Guenter Roeck <linux@roeck-us.net>
Subject: Re: [PATCH v4 7/8] hwmon: pwm-fan: Read PWM FAN configuration from
 device tree
Date: Mon, 23 Feb 2015 08:59:55 -0800
Message-ID: <20150223165955.GA9417@roeck-us.net>
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To: Lukasz Majewski <l.majewski@samsung.com>
Cc: Eduardo Valentin <edubezval@gmail.com>, Kamil Debski <k.debski@samsung.com>, Jean Delvare <jdelvare@suse.de>, Kukjin Kim <kgene@kernel.org>, lm-sensors@lm-sensors.org, Linux PM list <linux-pm@vger.kernel.org>, "linux-samsung-soc@vger.kernel.org" <linux-samsung-soc@vger.kernel.org>, devicetree@vger.kernel.org, Lukasz Majewski <l.majewski@majess.pl>, Kukjin Kim <kgene.kim@samsung.com>, linux-kernel@vger.kernel.org, Sjoerd Simons <sjoerd.simons@collabora.co.uk>, Abhilash Kesavan <kesavan.abhilash@gmail.com>, Abhilash Kesavan <a.kesavan@samsung.com>
List-Id: devicetree@vger.kernel.org

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