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

[Guenter Roeck]

On 02/08/2015 01:36 PM, Lukasz Majewski wrote:
> On Fri, 6 Feb 2015 10:36:57 -0800
> Guenter Roeck <linux@xxxxxxxxxxxx> 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@xxxxxxxxxxx>
> > > ---
> > > 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.

of_property_count_elems_of_size returns -EINVAL if np is NULL or if
there is no peoperty or prop->length % elem_size != 0, and -ENODATA
if there is no value associated with the property.

If -EINVAL is not an error, please no message. Noisy drivers are
just that, noisy.

> > > +	}
> > > +
> > > +	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.
You don't return an error, you return 0, at least in some circumstances.

> > 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.
It returns -ENOSYS if DT is not configured, which is still unacceptable.
And, again, if ret == 0 is an error, you should return an error code,
not display an error message and return 0.

Guenter

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