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

Guenter Roeck
2015-02-06T18:38:15Z

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@samsung.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