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

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Date:	Fri, 6 Feb 2015 10:36:57 -0800
From:	Guenter Roeck <linux@...ck-us.net>
To:	Lukasz Majewski <l.majewski@...sung.com>
Cc:	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,
	Lukasz Majewski <l.majewski@...ess.pl>,
	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, 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. Also, the message itself is wrong; the property may
well be there but have a wrong size.

> +	}
> +
> +	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). 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.

Guenter
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