linux-kernel - Re: [PATCH v2 2/3] arm64: dts: qcom: hamoa: Add the APSS watchdog

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Message-ID: <ms4r24li6bk3dvyjas5sor442jvkptz55yisdnaco6qdsyvsda@dt4lv3t366cg>
Date: Tue, 23 Dec 2025 18:00:48 +0200
From: Abel Vesa <abel.vesa@....qualcomm.com>
To: Konrad Dybcio <konrad.dybcio@....qualcomm.com>
Cc: Wim Van Sebroeck <wim@...ux-watchdog.org>,
        Guenter Roeck <linux@...ck-us.net>, Rob Herring <robh@...nel.org>,
        Krzysztof Kozlowski <krzk+dt@...nel.org>,
        Conor Dooley <conor+dt@...nel.org>,
        Rajendra Nayak <quic_rjendra@...cinc.com>,
        Bjorn Andersson <andersson@...nel.org>,
        Konrad Dybcio <konradybcio@...nel.org>,
        Stephan Gerhold <stephan.gerhold@...aro.org>,
        linux-arm-msm@...r.kernel.org, linux-watchdog@...r.kernel.org,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 2/3] arm64: dts: qcom: hamoa: Add the APSS watchdog

On 25-12-19 13:15:00, Konrad Dybcio wrote:
> On 12/19/25 11:00 AM, Abel Vesa wrote:
> > The watchdog support in EL1 is SBSA compliant, handled by Gunyah
> > hypervisor, but in EL2. the watchdog is an instance of the APSS WDT HW
> > block, same as older platforms. So describe the APSS WDT node and mark
> > it as reserved, as it will only be enabled in EL2 overlay.
> > 
> > Signed-off-by: Abel Vesa <abel.vesa@....qualcomm.com>
> > ---
> >  arch/arm64/boot/dts/qcom/hamoa.dtsi | 8 ++++++++
> >  1 file changed, 8 insertions(+)
> > 
> > diff --git a/arch/arm64/boot/dts/qcom/hamoa.dtsi b/arch/arm64/boot/dts/qcom/hamoa.dtsi
> > index a17900eacb20..b65dfad71c2f 100644
> > --- a/arch/arm64/boot/dts/qcom/hamoa.dtsi
> > +++ b/arch/arm64/boot/dts/qcom/hamoa.dtsi
> > @@ -8302,6 +8302,14 @@ gic_its: msi-controller@...40000 {
> >  			};
> >  		};
> >  
> > +		apss_watchdog: watchdog@...10000 {
> > +			compatible = "qcom,apss-wdt-x1e80100", "qcom,kpss-wdt";
> > +			reg = <0x0 0x17410000 0x0 0x1000>;
> > +			clocks = <&sleep_clk>;
> > +			interrupts = <GIC_SPI 0 IRQ_TYPE_EDGE_RISING>;
> > +			status = "reserved"; /* Accessible in EL2 only */
> 
> This is technically incorrect - it's not accessible if Gunyah is
> present, which is only somewhat related - if you run a different
> hypervisor which doesn't explicitly block access to this region, you
> can still access it even though Linux may be running at EL1

Fair enough. But in the case where you have a different hypervisor,
I guess the EL2 dtso should be used.

So, since AFAIK all devices come with Gunyah by default, it makes sense
to mark it as reserved (or disable it otherwise) and then enable it in EL2
dtso.