Re: [PATCH 1/2] DT: bindings: Add cooling cells for idle states

From: Daniel Lezcano <daniel.lezcano@linaro.org>
To: Rob Herring <robh@kernel.org>
Cc: Mark Rutland <mark.rutland@arm.com>,
	Amit Kucheria <amit.kucheria@linaro.org>,
	Geert Uytterhoeven <geert+renesas@glider.be>,
	Mauro Carvalho Chehab <mchehab+samsung@kernel.org>,
	"open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
	<devicetree@vger.kernel.org>,
	open list <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH 1/2] DT: bindings: Add cooling cells for idle states
Date: Sat, 11 Jan 2020 18:32:48 +0100	[thread overview]
Message-ID: <3b94b423-ca26-b96f-90fa-2662dbc523d8@linaro.org> (raw)
In-Reply-To: <20200108140333.GA12276@bogus>

Hi Rob,

On Wed, 8 Jan 2020 at 15:03, Rob Herring <robh@kernel.org> wrote:
>
> On Thu, Dec 19, 2019 at 11:19:27PM +0100, Daniel Lezcano wrote:
> > Add DT documentation to add an idle state as a cooling device. The CPU
> > is actually the cooling device but the definition is already used by
> > frequency capping. As we need to make cpufreq capping and idle
> > injection to co-exist together on the system in order to mitigate at
> > different trip points, the CPU can not be used as the cooling device
> > for idle injection. The idle state can be seen as an hardware feature
> > and therefore as a component for the passive mitigation.
> >
> > Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>
> > ---
> >  Documentation/devicetree/bindings/arm/idle-states.txt | 11 +++++++++++
> >  1 file changed, 11 insertions(+)
>
> This is now a schema in my tree. Can you rebase on that and I'll pick up
> the binding change.

Mmh, I'm now having some doubts about this binding because it will
restrict any improvement of the cooling device for the future.

It looks like adding a node to the CPU for the cooling device is more
adequate.
eg:
CPU0: cpu@300 {
   device_type = "cpu";
   compatible = "arm,cortex-a9";
   reg = <0x300>;
   /* cpufreq controls */
   operating-points = <998400 0
          800000 0
          400000 0
          200000 0>;
   clocks = <&prcmu_clk PRCMU_ARMSS>;
   clock-names = "cpu";
   clock-latency = <20000>;
   #cooling-cells = <2>;
   thermal-idle {
      #cooling-cells = <2>;
   };
};

[ ... ]

cooling-device = <&{/cpus/cpu@300/thermal-idle}
			THERMAL_NO_LIMIT THERMAL_NO_LIMIT>;

A quick test with different configurations combination shows it is much
more flexible and it is open for future changes.

What do you think?