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

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Message-ID: <e8af9692a9a54e44ad687bb8984fad7a@codeaurora.org>
Date:   Thu, 25 Mar 2021 10:50:57 +0530
From:   skakit@...eaurora.org
To:     Matthias Kaehlcke <mka@...omium.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

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,
Satya Priya