linux-kernel - Re: [RFC PATCH v2 2/3] hwmon: (adt7475) fan stall prevention

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Message-ID: <c690b3b0c33644528bdb1dd621d5773e@svr-chch-ex1.atlnz.lc>
Date:   Wed, 3 May 2017 20:44:52 +0000
From:   Chris Packham <Chris.Packham@...iedtelesis.co.nz>
To:     Guenter Roeck <linux@...ck-us.net>
CC:     "linux-hwmon@...r.kernel.org" <linux-hwmon@...r.kernel.org>,
        "jdelvare@...e.com" <jdelvare@...e.com>,
        Jonathan Corbet <corbet@....net>,
        "linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [RFC PATCH v2 2/3] hwmon: (adt7475) fan stall prevention

On 04/05/17 04:10, Guenter Roeck wrote:
> On Wed, May 03, 2017 at 12:40:08PM +1200, Chris Packham wrote:
>> By default adt7475 will stop the fans (pwm duty cycle 0%) when the
>> temperature drops past Tmin - hysteresis. Some systems want to keep the
>> fans moving even when the temperature drops so add new sysfs attributes
>> that configure the enhanced acoustics min 1-3 which allows the fans to
>> run at the minimum configure pwm duty cycle.
>>
>> Signed-off-by: Chris Packham <chris.packham@...iedtelesis.co.nz>
>> ---
>> Changes in v2:
>> - use pwmN_stall_dis as the attribute name. I think this describes the purpose
>>   pretty well. I went with a new attribute instead of overloading
>>   pwmN_auto_point1_pwm so this doesn't affect existing users.
>>
>>  Documentation/hwmon/adt7475 |  5 +++++
>>  drivers/hwmon/adt7475.c     | 50 +++++++++++++++++++++++++++++++++++++++++++++
>>  2 files changed, 55 insertions(+)
>>
>> diff --git a/Documentation/hwmon/adt7475 b/Documentation/hwmon/adt7475
>> index 0502f2b464e1..63507402cd4f 100644
>> --- a/Documentation/hwmon/adt7475
>> +++ b/Documentation/hwmon/adt7475
>> @@ -109,6 +109,11 @@ fan speed) is applied. PWM values range from 0 (off) to 255 (full speed).
>>  Fan speed may be set to maximum when the temperature sensor associated with
>>  the PWM control exceeds temp#_max.
>>
>> +At Tmin - hysteresis the PWM output can either be off (0% duty cycle) or at the
>> +minimum (i.e. auto_point1_pwm). This behaviour be configured using the
>> +pwm[1-*]_stall_dis sysfs attribute. A value of 0 means the fans will shut off.
>
> That is really an awkward attribute name. I'll have to think about this some
> more.

I agree. The other thing I considered was "halt" and using inverted 
logic so halt == 1 reflected the HW default of allowing fans to stop.