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Date:   Mon, 14 Jan 2019 11:29:24 +0530
From:   Viresh Kumar <viresh.kumar@linaro.org>
To:     Matthias Kaehlcke <mka@chromium.org>
Cc:     Amit Kucheria <amit.kucheria@linaro.org>,
        linux-kernel@vger.kernel.org, linux-arm-msm@vger.kernel.org,
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        dianders@chromium.org, David Brown <david.brown@linaro.org>,
        Rob Herring <robh+dt@kernel.org>,
        Mark Rutland <mark.rutland@arm.com>,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <devicetree@vger.kernel.org>, daniel.lezcano@linaro.org
Subject: Re: [PATCH v1 7/7] arm64: dts: sdm845: wireup the thermal trip
 points to cpufreq
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On 11-01-19, 11:58, Matthias Kaehlcke wrote:
> On Fri, Jan 11, 2019 at 09:16:53AM +0530, Viresh Kumar wrote:
> Just to gain a better understanding: is cpuidle cooling already
> available for arm64 (or is there a patch set)? I came across the
> relatively new idle injecting framework but it seems currently the
> only user is the Intel powerclamp driver.

Daniel was trying to upstream it earlier:

lore.kernel.org/lkml/1522945005-7165-7-git-send-email-daniel.lezcano@linaro.org

> > > even though only one will be active at any given
> > > time. However I wonder if we could change this:
> > 
> > I won't say it that way. I see it as all the CPUs are active during a
> > cooling state, i.e. they are all participating.
> 
> agreed, I was referring to the CPU cooling device, which (without
> cpuidle injection) could be considered a single device per freq domain.

Even without cpuidle injection all CPUs actually take part in cooling.

> > > For device tree based platform the above implies that cooling maps
> > > must include a list of all possible cooling devices of a frequency
> > > domain, even though only one of them will exist at any given time.
> > > 
> > > For example:
> > > 
> > > cooling-maps {
> > > 	map0 {
> > > 		trip = <&cpu_alert0>;
> > > 		cooling-device = <&CPU0 THERMAL_NO_LIMIT 4>,
> > > 				 <&CPU1 THERMAL_NO_LIMIT 4>,
> > > 				 <&CPU2 THERMAL_NO_LIMIT 4>,
> > > 				 <&CPU3 THERMAL_NO_LIMIT 4>;
> > > 	};
> > > 	map1 {
> > > 		trip = <&cpu_crit0>;
> > > 		cooling-device = <&CPU0 THERMAL_NO_LIMIT THERMAL_NO_LIMIT>,
> > > 				 <&CPU1 THERMAL_NO_LIMIT THERMAL_NO_LIMIT>,
> > > 				 <&CPU2 THERMAL_NO_LIMIT THERMAL_NO_LIMIT>,
> > > 				 <&CPU3 THERMAL_NO_LIMIT THERMAL_NO_LIMIT>;
> > 
> > This is the right thing to do hardware description wise, no matter
> > what the kernel does.
> 
> Not sure I would call it a hardware description. I'd say we pretend
> the thermal configuration is a hardware description so the DT folks
> don't yell at us ;-) IMO a CPU cooling device is an abstraction, I
> think there is no such IP block on most systems.

Right.

> It seems with cpuidle injection CPUs can perform cooling actions
> individually, with that I agree that representing them as individual
> cooling devices in the DT makes sense. Without that a cooling device
> per freq domain would seem a resonable abstraction.

But we actually have 4 different cooling devices no matter what. The only thing
is that they switch their cooling state together. And that shouldn't bother DT
is what I thought :)

> One of the reasons I dislike the above list of cooling devices is that
> it is repeated for different thermal-zone/cooling-maps, but I guess
> we have to live with that, would be nice if the DT would allow to do
> something like this:
> 
> thermal-zones {
> 	cooling_maps_fd0 : cooling-maps {
> 		map0 {
> 			trip = <&cpu_alert0>;
> 			cooling-device = <&CPU0 THERMAL_NO_LIMIT 4>,
> 					 <&CPU1 THERMAL_NO_LIMIT 4>,
> 					 <&CPU2 THERMAL_NO_LIMIT 4>,
> 					 <&CPU3 THERMAL_NO_LIMIT 4>;
> 		};
> 		map1 {
> 			trip = <&cpu_crit0>;
> 			cooling-device = <&CPU0 THERMAL_NO_LIMIT THERMAL_NO_LIMIT>,
> 					 <&CPU1 THERMAL_NO_LIMIT THERMAL_NO_LIMIT>,
> 					 <&CPU2 THERMAL_NO_LIMIT THERMAL_NO_LIMIT>,
> 					 <&CPU3 THERMAL_NO_LIMIT THERMAL_NO_LIMIT>;
> 	};
> 
> 	cpu0-thermal {
> 		...
> 		cooling-maps = @cooling_maps_fd0;
> 		...
> 	};
> 
> 	cpu1-thermal {
> 		...
> 		cooling-maps = @cooling_maps_fd0;
> 		...
> 	};
> 
> 	...
> };

Yeah, maybe. There aren't lot of examples of such duplication though if I
remember correctly.

-- 
viresh