linux-kernel - Re: [PATCH] arm64: dts: qcom: sc7280: Add PMIC peripherals for SC7280

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Date:   Tue, 30 Mar 2021 11:19:55 -0700
From:   Matthias Kaehlcke <mka@...omium.org>
To:     skakit@...eaurora.org
Cc:     Rob Herring <robh+dt@...nel.org>, Andy Gross <agross@...nel.org>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        linux-arm-msm@...r.kernel.org, linux-kernel@...r.kernel.org,
        devicetree@...r.kernel.org, kgunda@...eaurora.org
Subject: Re: [PATCH] arm64: dts: qcom: sc7280: Add PMIC peripherals for SC7280

On Thu, Mar 25, 2021 at 10:50:57AM +0530, skakit@...eaurora.org wrote:
> Hi Matthias,
> 
> On 2021-03-22 23:04, Matthias Kaehlcke wrote:
> > Hi Satya,
> > 
> > On Mon, Mar 22, 2021 at 06:50:47PM +0530, skakit@...eaurora.org wrote:
> > > Hi Matthias,
> > > 
> > > On 2021-03-13 02:10, Matthias Kaehlcke wrote:
> > > > Hi Satya,
> > > >
> > > > On Thu, Mar 11, 2021 at 04:10:29PM +0530, satya priya wrote:
> > > > > Add PM7325/PM8350C/PMK8350/PMR735A peripherals such as PON,
> > > > > GPIOs, RTC and other PMIC infra modules for SC7280.
> > > > >
> > > > > Signed-off-by: satya priya <skakit@...eaurora.org>
> > > > > ---
> > > > > This patch depends on base DT and board files for SC7280 to merge
> > > > > first
> > > > > https://lore.kernel.org/patchwork/project/lkml/list/?series=487403
> > > > >
> > > > >  arch/arm64/boot/dts/qcom/pm7325.dtsi  |  60 ++++++++++++++++++++
> > > > >  arch/arm64/boot/dts/qcom/pm8350c.dtsi |  60 ++++++++++++++++++++
> > > > >  arch/arm64/boot/dts/qcom/pmk8350.dtsi | 104
> > > > > ++++++++++++++++++++++++++++++++++
> > > > >  arch/arm64/boot/dts/qcom/pmr735a.dtsi |  60 ++++++++++++++++++++
> > > > >  arch/arm64/boot/dts/qcom/sc7280.dtsi  |   8 +++
> > > > >  5 files changed, 292 insertions(+)
> > > > >  create mode 100644 arch/arm64/boot/dts/qcom/pm7325.dtsi
> > > > >  create mode 100644 arch/arm64/boot/dts/qcom/pm8350c.dtsi
> > > > >  create mode 100644 arch/arm64/boot/dts/qcom/pmk8350.dtsi
> > > > >  create mode 100644 arch/arm64/boot/dts/qcom/pmr735a.dtsi
> > > > >
> > > > > diff --git a/arch/arm64/boot/dts/qcom/pm7325.dtsi
> > > > > b/arch/arm64/boot/dts/qcom/pm7325.dtsi
> > > > > new file mode 100644
> > > > > index 0000000..393b256
> > > > > --- /dev/null
> > > > > +++ b/arch/arm64/boot/dts/qcom/pm7325.dtsi
> > > > > @@ -0,0 +1,60 @@
> > > >
> > > > ...
> > > >
> > > > > +		polling-delay-passive = <100>;
> > > > > +		polling-delay = <0>;
> > > >
> > > > Are you sure that no polling delay is needed? How does the thermal
> > > > framework
> > > > detect that the temperatures is >= the passive trip point and that it
> > > > should
> > > > start polling at 'polling-delay-passive' rate?
> > > >
> > > 
> > > As the temp-alarm has interrupt support, whenever preconfigured
> > > threshold
> > > violates it notifies thermal framework, so I think the polling delay
> > > is not
> > > needed here.
> > 
> > From the documentation I found it's not clear to me how exactly these
> > interrupts work. Is a single interrupt triggered when the threshold is
> > violated or are there periodic (?) interrupts as long as the temperature
> > is above the stage 0 threshold?
> > 
> > Why is 'polling-delay-passive' passive needed if there are interrupts?
> > Maybe
> > to detect that the zone should transition from passive to no cooling
> > when the
> > temperature drops below the stage 0 threshold?
> 
> The PMIC TEMP_ALARM peripheral maintains an internal over-temperature stage:
> 0, 1, 2, or 3.  Stage 0 is normal operation below the lowest (stage 1)
> threshold [usually 95 C].  When in stage 1, the temperature is between the
> stage 1 and 2 thresholds [stage 2 threshold is usually 115 C].  Upon hitting
> the stage 3 threshold [usually 145 C], the PMIC hardware will automatically
> shut down the system.
> 
> The TEMP_ALARM IRQ fires on stage 0 -> 1 and 1 -> 0 transitions.  We
> therefore set polling-delay = <0> since there is no need for software to
> monitor the temperature periodically when operating in stage 0.  Upon
> crossing the stage 1 threshold, SW receives the IRQ and the thermal
> framework hits its first trip changing the thermal zone to passive mode.
> This then engages the 100 ms polling enabled via polling-delay-passive =
> <100>.  If the temperate keeps climbing and passes the stage 2 threshold,
> the thermal framework hits the second trip (which is critical) and it
> initiates an orderly shutdown.  If the temperature drops below the stage 1
> threshold, then the thermal framework exits passive mode and stops polling.
> This approach reduces/eliminates the software overhead when not at an
> elevated temperature.

Thanks for the clarification. With the interrupt only firing on stage 0 -> 1
and stage 1 -> 0 it makes sense. I was expecting interrupts on the other
transitions too.