RE: [EXT] Re: [PATCH v6] arm64: dts: ls1088a: add one more thermal zone node

[Andy Tang]

Thanks Viresh for your explanation.

BR,
Andy
> -----Original Message-----
> From: Viresh Kumar <viresh.kumar@xxxxxxxxxx>
> Sent: 2019å5æ10æ 18:12
> To: Andy Tang <andy.tang@xxxxxxx>
> Cc: Daniel Lezcano <daniel.lezcano@xxxxxxxxxx>; Shawn Guo
> <shawnguo@xxxxxxxxxx>; Leo Li <leoyang.li@xxxxxxx>; robh+dt@xxxxxxxxxx;
> mark.rutland@xxxxxxx; linux-arm-kernel@xxxxxxxxxxxxxxxxxxx;
> devicetree@xxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx;
> linux-pm@xxxxxxxxxxxxxxx; rui.zhang@xxxxxxxxx; edubezval@xxxxxxxxx
> Subject: Re: [EXT] Re: [PATCH v6] arm64: dts: ls1088a: add one more thermal
> zone node
> 
> Caution: EXT Email
> 
> On 10-05-19, 08:47, Andy Tang wrote:
> > + Viresh for help.
> >
> > > -----Original Message-----
> > > From: Daniel Lezcano <daniel.lezcano@xxxxxxxxxx>
> > > Sent: 2019å5æ10æ 15:17
> > > To: Andy Tang <andy.tang@xxxxxxx>; Shawn Guo
> <shawnguo@xxxxxxxxxx>
> > > Cc: Leo Li <leoyang.li@xxxxxxx>; robh+dt@xxxxxxxxxx;
> > > mark.rutland@xxxxxxx; linux-arm-kernel@xxxxxxxxxxxxxxxxxxx;
> > > devicetree@xxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx;
> > > linux-pm@xxxxxxxxxxxxxxx; rui.zhang@xxxxxxxxx; edubezval@xxxxxxxxx
> > > Subject: Re: [EXT] Re: [PATCH v6] arm64: dts: ls1088a: add one more
> > > thermal zone node
> > >
> > > Caution: EXT Email
> > >
> > > On 10/05/2019 05:40, Andy Tang wrote:
> > > >> -----Original Message-----
> > > >> From: Shawn Guo <shawnguo@xxxxxxxxxx>
> > > >> Sent: 2019å5æ10æ 11:14
> > > >> To: Andy Tang <andy.tang@xxxxxxx>
> > > >> Cc: Leo Li <leoyang.li@xxxxxxx>; robh+dt@xxxxxxxxxx;
> > > >> mark.rutland@xxxxxxx; linux-arm-kernel@xxxxxxxxxxxxxxxxxxx;
> > > >> devicetree@xxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx;
> > > >> linux-pm@xxxxxxxxxxxxxxx; daniel.lezcano@xxxxxxxxxx;
> > > >> rui.zhang@xxxxxxxxx; edubezval@xxxxxxxxx
> > > >> Subject: [EXT] Re: [PATCH v6] arm64: dts: ls1088a: add one more
> > > >> thermal zone node
> > > >>
> > > >> Caution: EXT Email
> > > >>
> > > >> On Tue, Apr 23, 2019 at 10:25:07AM +0800, Yuantian Tang wrote:
> > > >>> Ls1088a has 2 thermal sensors, core cluster and SoC platform.
> > > >>> Core cluster sensor is used to monitor the temperature of core
> > > >>> and SoC platform is for platform. The current dts only support the first
> sensor.
> > > >>> This patch adds the second sensor node to dts to enable it.
> > > >>>
> > > >>> Signed-off-by: Yuantian Tang <andy.tang@xxxxxxx>
> > > >>> ---
> > > >>> v6:
> > > >>>         - add cooling device map to cpu0-7 in platform node.
> > > > I like to explain a little. I think it makes sense that multiple
> > > > thermal zone
> > > map to same cooling device.
> > > > In this way, no matter which thermal zone raises a temp alarm, it
> > > > can call
> > > cooling device to chill out.
> > > > I also asked cpufreq maintainer about the cooling map issue, he
> > > > think it
> > > would be fine.
> 
> Yes, you asked me and I said it should be okay.
> 
> > > > I have tested and no issue found.
> > > >
> > > > Daniel, what's your thought?
> > >
> > > If there are multiple thermal zones, they will be managed by
> > > different instances of a thermal governor. Each instances will act
> > > on the shared cooling device and will collide in their decisions:
> > >
> > >  - If the sensors are closed, their behavior will be similar
> > > regarding the temperature. The governors may take the same decision
> > > for the cooling device. But in such case having just one thermal zone
> managed is enough.
> > >
> > >  - If the sensors are not closed, their behavior will be different
> > > regarding the temperature. The governors will take different
> > > decision regarding the cooling device (one will decrease the freq, other
> will increase the freq).
> > >
> > > As the thermal governors are not able to manage several thermal
> > > zones and there is one cooling device (the cpu cooling device), this
> > > setup won't work as expected IMO.
> > >
> > > The setup making sense is having a thermal zone per 'cluster' and a
> > > cooling device per 'cluster'. That means the platform has one clock line
> per 'cluster'.
> > > The thermal management happens in a self-contained thermal zone (one
> > > cooling device - one governor - one thermal zone).
> > >
> > > In the case of HMP, other combinations are possible to be optimal.
> 
> But not sure how I missed the obvious, though I do remember thinking about
> this.
> 
> So the problem is that the cpu_cooling driver will get requests in parallel to
> set different max frequencies and the last call will always win and may result
> in undesired outcome.
> 
> Sorry about creating the confusion.
> 
> --
> viresh