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

[Andy Tang <andy.tang@nxp.com>]

+ Viresh for help.

> -----Original Message-----
> From: Daniel Lezcano <daniel.lezcano@linaro.org>
> Sent: 2019年5月10日 15:17
> To: Andy Tang <andy.tang@nxp.com>; Shawn Guo <shawnguo@kernel.org>
> Cc: Leo Li <leoyang.li@nxp.com>; robh+dt@kernel.org;
> mark.rutland@arm.com; linux-arm-kernel@lists.infradead.org;
> devicetree@vger.kernel.org; linux-kernel@vger.kernel.org;
> linux-pm@vger.kernel.org; rui.zhang@intel.com; edubezval@gmail.com
> 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@kernel.org>
> >> Sent: 2019年5月10日 11:14
> >> To: Andy Tang <andy.tang@nxp.com>
> >> Cc: Leo Li <leoyang.li@nxp.com>; robh+dt@kernel.org;
> >> mark.rutland@arm.com; linux-arm-kernel@lists.infradead.org;
> >> devicetree@vger.kernel.org; linux-kernel@vger.kernel.org;
> >> linux-pm@vger.kernel.org; daniel.lezcano@linaro.org;
> >> rui.zhang@intel.com; edubezval@gmail.com
> >> 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@nxp.com>
> >>> ---
> >>> 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.
> > 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.
Hi Viresh,

I want to map multiple thermal zones to the same cooling device. The above is the discussion about it.
It seems reasonable. But I am not expert on this. Could you please provide some thoughts? Thanks.

BR,
Andy
> 
> 
> 
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