linux-kernel - RE: [EXT] Re: [PATCH] dt-bindings: thermal: Make cooling-maps property optional

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Message-ID: <VI1PR04MB4333A37E27148B4295C3E761F3020@VI1PR04MB4333.eurprd04.prod.outlook.com>
Date:   Fri, 24 May 2019 03:21:24 +0000
From:   Andy Tang <andy.tang@....com>
To:     Eduardo Valentin <edubezval@...il.com>
CC:     "rui.zhang@...el.com" <rui.zhang@...el.com>,
        "robh+dt@...nel.org" <robh+dt@...nel.org>,
        "daniel.lezcano@...aro.org" <daniel.lezcano@...aro.org>,
        "mark.rutland@....com" <mark.rutland@....com>,
        "linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [EXT] Re: [PATCH] dt-bindings: thermal: Make cooling-maps
 property optional

> -----Original Message-----
> From: Eduardo Valentin <edubezval@...il.com>
> Sent: 2019年5月24日 10:50
> To: Andy Tang <andy.tang@....com>
> Cc: rui.zhang@...el.com; robh+dt@...nel.org; daniel.lezcano@...aro.org;
> mark.rutland@....com; linux-pm@...r.kernel.org;
> devicetree@...r.kernel.org; linux-kernel@...r.kernel.org
> Subject: [EXT] Re: [PATCH] dt-bindings: thermal: Make cooling-maps property
> optional
> 
> Caution: EXT Email
> 
> On Wed, May 15, 2019 at 05:36:47PM +0800, Yuantian Tang wrote:
> > There may be no cooling device on system, or there are no enough
> > cooling devices for each thermal zone in multiple thermal zone cases
> > since cooling devices can't be shared.
> > So make this property optional to remove such limitations.
> 
> Yeah, I am  not sure that is enough reason to make this property optional.
> Let me maybe ask you why do you care creating a thermal zone if your control
> has no actions? Or rather, why bothering setting up a control that has no
> actuators?
No cooling-device map doesn't mean NO ACTIONS. There could be critic trips that trigger CPU reset or shutdown.
The root cause for it here is: there is no enough cooling device for each zone when multiple zone exist.
For example, for our ls2088a platform, there are 7 thermal zones, but we have only one cooling device which is cpufreq.
Due to this option limitation, multiple zones can't be supported.
I believe on most platform, there are only two type of cooling devices, cpufreq and fan. So how many cooling devices it could be?
So making the property optional is reasonable. We can assign cooling devices to certain thermal zones and leave the thermal zone with no cooling device taking default actions.

BR,
Andy
> 
> >
> > Signed-off-by: Yuantian Tang <andy.tang@....com>
> > ---
> >  .../devicetree/bindings/thermal/thermal.txt        |    4 ++--
> >  1 files changed, 2 insertions(+), 2 deletions(-)
> >
> > diff --git a/Documentation/devicetree/bindings/thermal/thermal.txt
> > b/Documentation/devicetree/bindings/thermal/thermal.txt
> > index ca14ba9..694e834 100644
> > --- a/Documentation/devicetree/bindings/thermal/thermal.txt
> > +++ b/Documentation/devicetree/bindings/thermal/thermal.txt
> > @@ -142,11 +142,11 @@ Required properties:
> >  - trips:             A sub-node which is a container of only trip point
> nodes
> >    Type: sub-node     required to describe the thermal zone.
> >
> > +
> > +Optional property:
> >  - cooling-maps:              A sub-node which is a container of only
> cooling device
> >    Type: sub-node     map nodes, used to describe the relation
> between trips
> >                       and cooling devices.
> > -
> > -Optional property:
> >  - coefficients:              An array of integers (one signed cell)
> containing
> >    Type: array                coefficients to compose a linear relation
> between
> >    Elem size: one cell        the sensors listed in the thermal-sensors
> property.
> > --
> > 1.7.1
> >