linux-kernel - Re: [PATCH V2 7/9] hwmon: pwm-fan: add sysfs node to read rpm of fan

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Date:   Tue, 20 Mar 2018 23:09:52 -0700
From:   Guenter Roeck <linux@...ck-us.net>
To:     Rajkumar Rampelli <rrajk@...dia.com>, robh+dt@...nel.org,
        mark.rutland@....com, thierry.reding@...il.com,
        jonathanh@...dia.com, jdelvare@...e.com, corbet@....net,
        catalin.marinas@....com, will.deacon@....com,
        kstewart@...uxfoundation.org, gregkh@...uxfoundation.org,
        pombredanne@...b.com, mmaddireddy@...dia.com,
        mperttunen@...dia.com, arnd@...db.de, timur@...eaurora.org,
        andy.gross@...aro.org, xuwei5@...ilicon.com, elder@...aro.org,
        heiko@...ech.de, krzk@...nel.org, ard.biesheuvel@...aro.org
Cc:     devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-pwm@...r.kernel.org, linux-tegra@...r.kernel.org,
        linux-hwmon@...r.kernel.org, linux-doc@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, ldewangan@...dia.com
Subject: Re: [PATCH V2 7/9] hwmon: pwm-fan: add sysfs node to read rpm of fan

On 03/20/2018 09:40 PM, Rajkumar Rampelli wrote:
> Add fan device attribute fan1_input in pwm-fan driver
> to read speed of fan in rotations per minute.
> 
> Signed-off-by: Rajkumar Rampelli <rrajk@...dia.com>
> ---
> 
> V2: Removed generic-pwm-tachometer driver and using pwm-fan driver as per suggestions
>      to read fan speed.
>      Added fan device attribute to report speed of fan in rpms through hwmon sysfs.
> 
>   drivers/hwmon/pwm-fan.c | 23 +++++++++++++++++++++++
>   1 file changed, 23 insertions(+)
> 
> diff --git a/drivers/hwmon/pwm-fan.c b/drivers/hwmon/pwm-fan.c
> index 70cc0d1..8dda209 100644
> --- a/drivers/hwmon/pwm-fan.c
> +++ b/drivers/hwmon/pwm-fan.c
> @@ -98,11 +98,34 @@ static ssize_t show_pwm(struct device *dev,
>   	return sprintf(buf, "%u\n", ctx->pwm_value);
>   }
>   
> +static ssize_t show_rpm(struct device *dev, struct device_attribute *attr,
> +			char *buf)
> +{
> +	struct pwm_fan_ctx *ptt = dev_get_drvdata(dev);
> +	struct pwm_device *pwm = ptt->pwm;
> +	struct pwm_capture result;
> +	unsigned int rpm = 0;
> +	int ret;
> +
> +	ret = pwm_capture(pwm, &result, 0);
> +	if (ret < 0) {
> +		pr_err("Failed to capture PWM: %d\n", ret);
> +		return ret;
> +	}
> +
> +	if (result.period)
> +		rpm = DIV_ROUND_CLOSEST_ULL(60ULL * NSEC_PER_SEC,
> +					    result.period);
> +
> +	return sprintf(buf, "%u\n", rpm);
> +}
>   
>   static SENSOR_DEVICE_ATTR(pwm1, S_IRUGO | S_IWUSR, show_pwm, set_pwm, 0);
> +static SENSOR_DEVICE_ATTR(fan1_input, 0444, show_rpm, NULL, 0);
>   
>   static struct attribute *pwm_fan_attrs[] = {
>   	&sensor_dev_attr_pwm1.dev_attr.attr,
> +	&sensor_dev_attr_fan1_input.dev_attr.attr,

This doesn't make sense. The same pwm can not both control the fan speed
and report it.

Guenter

>   	NULL,
>   };
>   
>