linux-kernel - Re: [PATCH v4 7/8] hwmon: pwm-fan: Read PWM FAN configuration from device tree

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Date:	Fri, 20 Feb 2015 16:26:27 -0800
From:	Guenter Roeck <linux@...ck-us.net>
To:	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>
CC:	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 v4 7/8] hwmon: pwm-fan: Read PWM FAN configuration from
 device tree

On 02/18/2015 02:07 AM, 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
> Changes for v4:
> - dev_err() has been removed from pwm_fan_of_get_cooling_data()
> - Returning -EINVAL when "cooling-levels" are defined in DT, but doesn't
>    have the value
> ---
>   drivers/hwmon/pwm-fan.c | 52 ++++++++++++++++++++++++++++++++++++++++++++++++-
>   1 file changed, 51 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/hwmon/pwm-fan.c b/drivers/hwmon/pwm-fan.c
> index bd42d39..82cd06a 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 +103,48 @@ 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)
> +		return 0;

The function returns -EINVAL if there is no such property,
but also if prop->length % elem_size != 0. The latter _would_
be an error.

Overall I don't entirely understand why you do not call
of_find_property first. If that returns NULL, you would know for sure
that the property does not exist, and you would not have to second
guess the returned error from of_property_count_elems_of_size.

On a side note, there is of_property_count_u32_elems() to count
properties of size u32.

> +
> +	if (ret <= 0) {
> +		dev_err(dev, "Wrong data!\n");
> +		return ret ? ret : -EINVAL;
> +	}

If devicetree is not configured, of_property_count_elems_of_size
returns -ENOSYS, which is returned, causing the driver to fail loading.

> +
> +	num = ret;
> +	ctx->pwm_fan_cooling_levels = devm_kzalloc(dev, num * sizeof(u32),
> +						   GFP_KERNEL);
> +	if (!ctx->pwm_fan_cooling_levels)
> +		return -ENOMEM;
> +
> +	ret = of_property_read_u32_array(np, "cooling-levels",
> +					 ctx->pwm_fan_cooling_levels, num);
> +	if (ret) {
> +		dev_err(dev, "Property 'cooling-levels' cannot be read!\n");
> +		return ret;
> +	}
> +
> +	for (i = 0; i < num; i++) {
> +		if (ctx->pwm_fan_cooling_levels[i] > MAX_PWM) {
> +			dev_err(dev, "PWM fan state[%d]:%d > %d\n", i,
> +				ctx->pwm_fan_cooling_levels[i], MAX_PWM);
> +			return -EINVAL;
> +		}
> +	}
> +
> +	ctx->pwm_fan_max_state = num - 1;
> +
> +	return 0;
> +}
> +
>   static int pwm_fan_probe(struct platform_device *pdev)
>   {
>   	struct device *hwmon;
> @@ -145,6 +190,11 @@ static int pwm_fan_probe(struct platform_device *pdev)
>   		pwm_disable(ctx->pwm);
>   		return PTR_ERR(hwmon);
>   	}
> +
> +	ret = pwm_fan_of_get_cooling_data(&pdev->dev, ctx);
> +	if (ret)
> +		return ret;
> +
>   	return 0;
>   }
>
>

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