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

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Message-ID: <700e0aa1-2ac1-4829-9469-0179511982e8@oss.qualcomm.com>
Date: Tue, 23 Dec 2025 18:19:50 +0100
From: Konrad Dybcio <konrad.dybcio@....qualcomm.com>
To: Abel Vesa <abel.vesa@....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 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 */

?

The patch looks good otherwise

Konrad