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Date:   Tue, 22 Jan 2019 10:18:22 -0800
From:   Matthias Kaehlcke <mka@chromium.org>
To:     Amit Kucheria <amit.kucheria@linaro.org>
Cc:     LKML <linux-kernel@vger.kernel.org>,
        linux-arm-msm <linux-arm-msm@vger.kernel.org>,
        Bjorn Andersson <bjorn.andersson@linaro.org>,
        Viresh Kumar <viresh.kumar@linaro.org>,
        Eduardo Valentin <edubezval@gmail.com>,
        Andy Gross <andy.gross@linaro.org>,
        Taniya Das <tdas@codeaurora.org>,
        Stephen Boyd <swboyd@chromium.org>,
        Douglas Anderson <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>
Subject: Re: [PATCH v2 8/9] arm64: dts: sdm845: wireup the thermal trip
 points to cpufreq
Message-ID: <20190122181822.GF261387@google.com>
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On Mon, Jan 21, 2019 at 11:40:45PM +0530, Amit Kucheria wrote:
> On Tue, Jan 15, 2019 at 3:31 AM Matthias Kaehlcke <mka@chromium.org> wrote:
> >
> > On Mon, Jan 14, 2019 at 03:51:10PM +0530, Amit Kucheria wrote:
> > > Since all cpus in the big and little clusters, respectively, are in the
> > > same frequency domain, use all of them for mitigation in the
> > > cooling-map. We end up with two cooling devices - one each for the big
> > > and little clusters.
> > >
> > > At the lower trip points we restrict ourselves to throttling only a few
> > > OPPs. At higher trip temperatures, allow ourselves to be throttled to
> > > any extent.
> > >
> > > Signed-off-by: Amit Kucheria <amit.kucheria@linaro.org>
> > > ---
> > >  arch/arm64/boot/dts/qcom/sdm845.dtsi | 177 ++++++++++++++++++++++++---
> > >  1 file changed, 161 insertions(+), 16 deletions(-)
> > >
> > > diff --git a/arch/arm64/boot/dts/qcom/sdm845.dtsi b/arch/arm64/boot/dts/qcom/sdm845.dtsi
> > > index fb7da678b116..7973e88bdf94 100644
> > > --- a/arch/arm64/boot/dts/qcom/sdm845.dtsi
> > > +++ b/arch/arm64/boot/dts/qcom/sdm845.dtsi
> > >
> > > ...
> > >
> > > @@ -1719,18 +1728,35 @@
> > >                       thermal-sensors = <&tsens0 1>;
> > >
> > >                       trips {
> > > -                             cpu_alert0: trip0 {
> > > +                             cpu0_alert0: trip-point@0 {
> >
> > Thanks for adapting the trip point names and labels in anticipation of
> > further additions!
> >
> > Seems you aren't overly convinced about the 'target/threshold'
> > terminology used by some other arm64 platforms ;-)
> 
> target and threshold have an air of finality to them and doesn't lend
> itself to having a few trip points on the way to the critical trip,
> IMO.
> 
> Let me know if you feel otherwise.

I can see your point, and it's also true that target/threshold seem to
imply the use of power_allocator, which may not always be the case.

> > >                                       temperature = <95000>;
> > >                                       hysteresis = <2000>;
> > >                                       type = "passive";
> > >                               };
> >
> > I realized that we still have the potential problem of a name change
> > in the trip point node name if a 'threshold' node for IPA is added,
> > since this node will have a lower temperature than 95°. If this is
> > something to be concerned about it might be worth to add that extra
> > trip point already to avoid headaches or funky trip point enumeration,
> > even if we know that the value might not be the final one.
> 
> I will squash both the DT changes in to a single change introducing 2
> passive trips and 1 critical trip to avoid the churn.

Sounds good, thanks!

> See if you like it better.

I didn't really dislike it, was just wondering if renaming nodes could
break existing users. I imagine it's not a huge problem after all,
since users with an older kernel version won't see the DT change and
probably should use the phandle anyway.

> > (I'm aware that we are also changing the node names and labels right
> > now, it seems less problematic at this point since the SDM845 thermal
> > zones are a fairly recent addition)
> >
> > > -                             cpu_crit0: trip1 {
> > > +                             cpu0_crit: cpu_crit@0 {
> >
> > nit: does the @0 add any value here? IIUC there can be only one
> > critical trip point, hence there will never be a cpu_crit@1 or
> > higher.
> 
> Agreed. Will remove.
> 
> > >                                       temperature = <110000>;
> > >                                       hysteresis = <1000>;
> > >                                       type = "critical";
> > >                               };
> > >                       };
> > > +
> > > +                     cooling-maps {
> > > +                             map0 {
> > > +                                     trip = <&cpu0_alert0>;
> > > +                                     cooling-device = <&CPU0 THERMAL_NO_LIMIT 4>,
> > > +                                                      <&CPU1 THERMAL_NO_LIMIT 4>,
> > > +                                                      <&CPU2 THERMAL_NO_LIMIT 4>,
> > > +                                                      <&CPU3 THERMAL_NO_LIMIT 4>;
> > > +                             };
> >
> > Out of curiosity: how did you determing the max cooling state of 4?
> 
> Just some basic testing by pinning a dhrystone benchmark to each of
> the cores along with some stress-ng threads. Lopping off the top 4
> OPPs seemed to mitigate anything I could throw at the board.

Thanks for sharing your approach!

> I'm unable to do the "device in a closed car on a hot summer day" type
> of tests on the dev board. Nevertheless, I've changed the patch now to
> only remove the boost frequency at 75 degrees and then full throttling
> at 95 degrees.
> 
> I'd appreciate more "real world" testing to validate these.

Sure, we'll run some tests with the new configuration on our site.

Thanks

Matthias