linux-kernel - Re: [PATCH v3 7/8] hwmon: pwm-fan: Read PWM FAN configuration from device tree

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Date:	Sun, 8 Feb 2015 22:36:40 +0100
From:	Lukasz Majewski <l.majewski@...ess.pl>
To:	Guenter Roeck <linux@...ck-us.net>
Cc:	Lukasz Majewski <l.majewski@...sung.com>,
	Eduardo Valentin <edubezval@...il.com>,
	Kamil Debski <k.debski@...sung.com>,
	Jean Delvare <jdelvare@...e.de>, Kukjin Kim <kgene@...nel.org>,
	lm-sensors@...sensors.org,
	Linux PM list <linux-pm@...r.kernel.org>,
	"linux-samsung-soc@...r.kernel.org" 
	<linux-samsung-soc@...r.kernel.org>, devicetree@...r.kernel.org,
	Kukjin Kim <kgene.kim@...sung.com>,
	linux-kernel@...r.kernel.org,
	Sjoerd Simons <sjoerd.simons@...labora.co.uk>,
	Abhilash Kesavan <kesavan.abhilash@...il.com>,
	Abhilash Kesavan <a.kesavan@...sung.com>
Subject: Re: [PATCH v3 7/8] hwmon: pwm-fan: Read PWM FAN configuration from
 device tree

On Fri, 6 Feb 2015 10:36:57 -0800
Guenter Roeck <linux@...ck-us.net> wrote:

> On Fri, Feb 06, 2015 at 05:59:07PM +0100, Lukasz Majewski wrote:
> > This patch provides code for reading PWM FAN configuration data via
> > device tree. The pwm-fan can work with full speed when configuration
> > is not provided. However, errors are propagated when wrong DT
> > bindings are found.
> > Additionally the struct pwm_fan_ctx has been extended.
> > 
> > Signed-off-by: Lukasz Majewski <l.majewski@...sung.com>
> > ---
> > Changes for v2:
> > - Rename pwm_fan_max_states to pwm_fan_cooling_levels
> > - Moving pwm_fan_of_get_cooling_data() call after setting end
> > enabling PWM FAN
> > - pwm_fan_of_get_cooling_data() now can fail - preserving old
> > behaviour
> > - Remove unnecessary dev_err() call
> > Changes for v3:
> > - Patch's headline has been reedited
> > - pwm_fan_of_get_cooling_data() return code is now being checked.
> > - of_property_count_elems_of_size() is now used instead
> > of_find_property()
> > - More verbose patch description added
> > ---
> >  drivers/hwmon/pwm-fan.c | 54
> > ++++++++++++++++++++++++++++++++++++++++++++++++- 1 file changed,
> > 53 insertions(+), 1 deletion(-)
> > 
> > diff --git a/drivers/hwmon/pwm-fan.c b/drivers/hwmon/pwm-fan.c
> > index 870e100..f3f5843 100644
> > --- a/drivers/hwmon/pwm-fan.c
> > +++ b/drivers/hwmon/pwm-fan.c
> > @@ -30,7 +30,10 @@
> >  struct pwm_fan_ctx {
> >  	struct mutex lock;
> >  	struct pwm_device *pwm;
> > -	unsigned char pwm_value;
> > +	unsigned int pwm_value;
> > +	unsigned int pwm_fan_state;
> > +	unsigned int pwm_fan_max_state;
> > +	unsigned int *pwm_fan_cooling_levels;
> >  };
> >  
> >  static int  __set_pwm(struct pwm_fan_ctx *ctx, unsigned long pwm)
> > @@ -100,6 +103,50 @@ static struct attribute *pwm_fan_attrs[] = {
> >  
> >  ATTRIBUTE_GROUPS(pwm_fan);
> >  
> > +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;
> > +
> > +	ret = of_property_count_elems_of_size(np, "cooling-levels",
> > +					      sizeof(u32));
> > +
> > +	if (ret == -EINVAL) {
> > +		dev_err(dev, "Property 'cooling-levels' not
> > found\n");
> > +		return 0;
> 
> Returning 0 is obviously not an error, otherwise you would not return
> 0 here. So dev_err is wrong.

pr_info would be more appropriate here.

> Also, the message itself is wrong; the
> property may well be there but have a wrong size.

As fair as I remember the -EINVAL is set only when the property is not
defined. Such situation is correct and our pwm-fan driver should work
with or without it.

> 
> > +	}
> > +
> > +	if (ret <= 0) {
> > +		dev_err(dev, "Wrong data!\n");
> > +		return ret;
> > +	}
> 
> This will result in the driver failing to load if devicetree is not
> configured (of_property_count_elems_of_size will return -ENOSYS).

As you pointed out in the comment to v2:

It is OK if the "cooling-levels" is not defined in DT. However, if it
has broken definition, then we should return error. This is what we do
here.

> This is not acceptable. Also, if the call returns 0 you don't return
> an error but display a "Wrong data!" error message. Either it is an
> error or it is not, but not both.

This is an error. "cooling-levels" with zero elements is regarded as a
broken property.

> 
> Guenter

Best regards,
Lukasz Majewski

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