linux-kernel - Re: [PATCH RFC 1/3] dt-bindings: hwmon: Add tachometer interrupt to pwm-fan

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Date:   Wed, 30 Jan 2019 12:35:25 -0800
From:   Guenter Roeck <linux@...ck-us.net>
To:     Stefan Wahren <stefan.wahren@...e.com>
Cc:     Kamil Debski <kamil@...as.org>,
        Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>,
        Jean Delvare <jdelvare@...e.com>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        linux-hwmon@...r.kernel.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH RFC 1/3] dt-bindings: hwmon: Add tachometer interrupt to
 pwm-fan

On Wed, Jan 30, 2019 at 09:23:31PM +0100, Stefan Wahren wrote:
> Hi Guenter,
> 
> > Guenter Roeck <linux@...ck-us.net> hat am 30. Januar 2019 um 18:28 geschrieben:
> > 
> > 
> > On Wed, Jan 30, 2019 at 04:07:05PM +0100, Stefan Wahren wrote:
> > > This adds the tachometer interrupt to the pwm-fan binding, which is
> > > necessary for RPM support.
> > > 
> > > Signed-off-by: Stefan Wahren <stefan.wahren@...e.com>
> > > ---
> > >  Documentation/devicetree/bindings/hwmon/pwm-fan.txt | 3 +++
> > >  1 file changed, 3 insertions(+)
> > > 
> > > diff --git a/Documentation/devicetree/bindings/hwmon/pwm-fan.txt b/Documentation/devicetree/bindings/hwmon/pwm-fan.txt
> > > index 49ca5d8..7f69b0b 100644
> > > --- a/Documentation/devicetree/bindings/hwmon/pwm-fan.txt
> > > +++ b/Documentation/devicetree/bindings/hwmon/pwm-fan.txt
> > > @@ -8,6 +8,9 @@ Required properties:
> > >  
> > >  Optional properties:
> > >  - fan-supply    : phandle to the regulator that provides power to the fan
> > > +- interrupts    : contains a single interrupt specifier which describes the
> > > +                  tachometer pin output of a 2 pulse-per-revolution fan.
> > > +                  See interrupt-controller/interrupts.txt for the format.
> > 
> > So a hypothetical {1,4} pulse-per-revolution fan would explicitly not be
> > supported ? Why ?
> 
> i could add an additional property to specify the pulse per revolution and use the 2 as default (according to the Intel spec for 4 pin pwm fan) which should fit in most cases.
> 
That would be a possibility and make sense, but that is not
the point here.  The "interrupts" property does not and should
not care how many pulses per revolution the fan provides.

Guenter