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

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Message-ID: <d4o6j5sxlpyggvbeifjmctjvxsvvmntkyrv4qybb6rgwgv75kg@hdwrecjykb3j>
Date: Wed, 24 Dec 2025 11:48:16 +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 25-12-23 18:19:50, Konrad Dybcio wrote:
> On 12/23/25 5:00 PM, Abel Vesa wrote:
> > 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.
> 
> I'm just stingy about the wording. Perhaps:
> 
> status = "reserved"; /* Reserved by Gunyah */
> 
> ?

Sure, will do.

> 
> The patch looks good otherwise
> 
> Konrad

Thanks for reviewing,
Abel