linux-kernel - Re: [PATCH v1 4/4] hwmon: add driver for the Microchip LAN966x SoC

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Date:   Sun, 27 Mar 2022 16:18:28 +0200
From:   Michael Walle <michael@...le.cc>
To:     Guenter Roeck <linux@...ck-us.net>
Cc:     Jean Delvare <jdelvare@...e.com>, Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzk+dt@...nel.org>,
        linux-hwmon@...r.kernel.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v1 4/4] hwmon: add driver for the Microchip LAN966x SoC

Am 2022-03-27 03:34, schrieb Guenter Roeck:

>> +	/*
>> +	 * Data is given in pulses per second. According to the hwmon ABI we
>> +	 * have to assume two pulses per revolution.
> 
> The hwmon ABI doesn't make any such assumptions. It wants to see RPM,
> that is all. Pulses per revolution is a fan property.

There is fanY_pulses according to 
Documentation/ABI/testing/sysfs-class-hwmon:

   Should only be created if the chip has a register to configure
   the number of pulses. In the absence of such a register (and
   thus attribute) the value assumed by all devices is 2 pulses
   per fan revolution.

The hardware returns just the pulses per second. Doesn't that
mean I have to divide that value by two?

>> +	 */
>> +	*val = FIELD_GET(FAN_CNT_DATA, data) * 60 / 2;

.. otherwise this should then be
*val = FIELD_GET(FAN_CNT_DATA, data) * 60;


>> +
>> +	return 0;
>> +}
>> +
>> +static int lan966x_hwmon_read_pwm(struct device *dev, long *val)
>> +{
>> +	struct lan966x_hwmon *hwmon = dev_get_drvdata(dev);
>> +	unsigned int data;
>> +	int ret;
>> +
>> +	ret = regmap_read(hwmon->regmap_fan, FAN_CFG, &data);
>> +	if (ret < 0)
>> +		return ret;
>> +
>> +	*val = FIELD_GET(FAN_CFG_DUTY_CYCLE, data);
>> +
>> +	return 0;
>> +}
>> +
>> +static int lan966x_hwmon_read_pwm_freq(struct device *dev, long *val)
>> +{
>> +	struct lan966x_hwmon *hwmon = dev_get_drvdata(dev);
>> +	unsigned long rate = clk_get_rate(hwmon->clk);
> 
> Is that a dynamic frequency ? If not, it would be better to read it 
> once
> and store it in struct lan966x_hwmon.

yes it is configurable, actually. See lan966x_hwmon_write_pwm_freq().

-michael