linux-kernel - Re: [PATCH v2] arm64: dts: ls1088a: add one more thermal zone node

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Date:   Wed, 20 Mar 2019 16:18:55 +0800
From:   Shawn Guo <shawnguo@...nel.org>
To:     Andy Tang <andy.tang@....com>
Cc:     Daniel Lezcano <daniel.lezcano@...aro.org>,
        "mark.rutland@....com" <mark.rutland@....com>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Leo Li <leoyang.li@....com>,
        "edubezval@...il.com" <edubezval@...il.com>,
        "robh+dt@...nel.org" <robh+dt@...nel.org>,
        "rui.zhang@...el.com" <rui.zhang@...el.com>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH v2] arm64: dts: ls1088a: add one more thermal zone node

On Fri, Mar 08, 2019 at 09:57:09AM +0000, Andy Tang wrote:
> 
> 
> > -----Original Message-----
> > From: Daniel Lezcano <daniel.lezcano@...aro.org>
> > Sent: 2019年3月8日 17:28
> > To: Andy Tang <andy.tang@....com>; Shawn Guo <shawnguo@...nel.org>
> > Cc: Leo Li <leoyang.li@....com>; robh+dt@...nel.org; mark.rutland@....com;
> > linux-arm-kernel@...ts.infradead.org; devicetree@...r.kernel.org;
> > linux-kernel@...r.kernel.org; linux-pm@...r.kernel.org; rui.zhang@...el.com;
> > edubezval@...il.com
> > Subject: Re: [PATCH v2] arm64: dts: ls1088a: add one more thermal zone node
> > 
> > On 08/03/2019 03:07, Andy Tang wrote:
> > >
> > >
> > >> -----Original Message-----
> > >> From: Daniel Lezcano <daniel.lezcano@...aro.org>
> > >> Sent: 2019年3月7日 17:15
> > >> To: Andy Tang <andy.tang@....com>; Shawn Guo <shawnguo@...nel.org>
> > >> Cc: Leo Li <leoyang.li@....com>; robh+dt@...nel.org;
> > >> mark.rutland@....com; linux-arm-kernel@...ts.infradead.org;
> > >> devicetree@...r.kernel.org; linux-kernel@...r.kernel.org;
> > >> linux-pm@...r.kernel.org; rui.zhang@...el.com; edubezval@...il.com
> > >> Subject: Re: [PATCH v2] arm64: dts: ls1088a: add one more thermal
> > >> zone node
> > >>
> > >>>>> PS: In order to keep consistency to the first thermal-zone node,
> > >>>>> there will be "WARNING: line over 80 characters" warnings.
> > >>>>>
> > >>>>>  arch/arm64/boot/dts/freescale/fsl-ls1088a.dtsi |   43
> > >>>> +++++++++++++++++++++--
> > >>>>>  1 files changed, 39 insertions(+), 4 deletions(-)
> > >>>>>
> > >>>>> diff --git a/arch/arm64/boot/dts/freescale/fsl-ls1088a.dtsi
> > >>>>> b/arch/arm64/boot/dts/freescale/fsl-ls1088a.dtsi
> > >>>>> index 661137f..9f52bc9 100644
> > >>>>> --- a/arch/arm64/boot/dts/freescale/fsl-ls1088a.dtsi
> > >>>>> +++ b/arch/arm64/boot/dts/freescale/fsl-ls1088a.dtsi
> > >>>>> @@ -129,19 +129,19 @@
> > >>>>>  	};
> > >>>>>
> > >>>>>  	thermal-zones {
> > >>>>> -		cpu_thermal: cpu-thermal {
> > >>>>> +		ccu {
> > >>>>
> > >>>> Is this change really necessary?  What does 'ccu' stand for?
> > >>> I think so. ccu stands for core cluster unit. cpu is too general.
> > >>> On some platforms, there are more than one core clusters.
> > >>> At least we should change it to "core cluster" if short form is not
> > appropriate.
> > >>
> > >> If the sensor is a the cluster level, 'cluster' is enough. IMHO, no
> > >> need to give a description of what contains the cluster, otherwise
> > >> you will end up with a 'core-gpu-cluster-l2' name.
> > > If cluster is specific to core, we can use cluster instead. But I don't think so.
> > > Cluster may refer to "core cluster", "GPU cluster" etc.
> > > So, I think "core-cluster" is ok.
> > > If core was divided to several clusters, we can name it as "core-cluster1",
> > "core-cluster2" etc.
> > > If GPU was divided to several clusters we can name it as "gpu-cluster1",
> > "gpu-cluster2" etc.
> > 
> > 
> > Hi Andy,
> > 
> > I think there is a confusion around the 'cpu' term and 'cluster'.
> > 
> > ARM would like to see the 'cluster' word to disappear, so whenever possible we
> > should avoid it.
> > 
> > From the hardware side, 'CPU' is usually used to describe the physical chip
> > containing the cores+cache.
> > 
> > From the software side, 'CPU' is usually used to describe the logical process
> > unit, aka a core or a hyper-thread.
> > 
> > As we are in the DT, so describing the hardware, the CPU refers to the group
> > cores+caches.
> > 
> > From my POV, using 'cpu' for the group of cores and 'gpu' for the graphic
> > sounds ok, and so far that is what is used for the other platforms.
> > 
> > If you change the name, that may give the feeling there is something special
> > with those thermal zones.
> 
> Thanks Daniel for your detailed explanations.
> 
> But as you said 'CPU' is usually used to describe the physical chip.

Here is how I would understand Daniel's comments:

  CPU = cores + caches
  physical chip = SoC = CPU + GPU + peripherals ...

> So if we name it as CPU, it sounds like this temperature sensor is monitoring the whole chip.
> That's not true in our case.
> 
> Take ls2088a for example:
> In ls2088a SoC, there are 7 temperature sensors. Please note that they are all located in SoC.
> The placement of the temperature sensors are showed below:
> 
> Sensor ID		placement
> 1			DDR controller 1
> 2			DDR controller 2
> 3			DDR controller 3
> 4			core cluster 1
> 5 			core cluster 2
> 6 			core cluster 3
> 7 			core cluster 4
> 
> Apparently using CPU or CPU-cluster is not appropriate. Core-cluster is better.

So using CPU is appropriate for me, less confusing, more consistent with
other platforms.

Shawn