linux-kernel - Re: [PATCH v4 3/5] dt-bindings: watchdog: qcom-wdt: Document qcom,imem property

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Message-ID: <85e30c0c-ea77-47da-9fd9-4293c7a78c75@oss.qualcomm.com>
Date: Thu, 22 May 2025 17:45:12 +0200
From: Konrad Dybcio <konrad.dybcio@....qualcomm.com>
To: Krzysztof Kozlowski <krzk@...nel.org>,
        Konrad Dybcio <konrad.dybcio@....qualcomm.com>,
        Kathiravan Thirumoorthy <kathiravan.thirumoorthy@....qualcomm.com>
Cc: Rob Herring <robh@...nel.org>, Krzysztof Kozlowski <krzk+dt@...nel.org>,
        Conor Dooley <conor+dt@...nel.org>,
        Bjorn Andersson <andersson@...nel.org>,
        Konrad Dybcio <konradybcio@...nel.org>,
        Wim Van Sebroeck <wim@...ux-watchdog.org>,
        Guenter Roeck
 <linux@...ck-us.net>,
        Rajendra Nayak <quic_rjendra@...cinc.com>,
        linux-arm-msm@...r.kernel.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-watchdog@...r.kernel.org
Subject: Re: [PATCH v4 3/5] dt-bindings: watchdog: qcom-wdt: Document
 qcom,imem property

On 5/21/25 8:53 AM, Krzysztof Kozlowski wrote:
> On 20/05/2025 18:00, Konrad Dybcio wrote:
>> On 5/20/25 9:25 AM, Krzysztof Kozlowski wrote:
>>> On Mon, May 19, 2025 at 02:04:03PM GMT, Kathiravan Thirumoorthy wrote:
>>>> Document the "qcom,imem" property for the watchdog device on Qualcomm
>>>> IPQ platforms. Use this property to extract the restart reason from
>>>> IMEM, which is updated by XBL. Populate the watchdog's bootstatus sysFS
>>>> entry with this information, when the system reboots due to a watchdog
>>>> timeout.
>>>>
>>>> Describe this property for the IPQ5424 watchdog device and extend support
>>>> to other targets subsequently.
>>>>
>>>> Signed-off-by: Kathiravan Thirumoorthy <kathiravan.thirumoorthy@....qualcomm.com>
>>>> ---
>>>> Changes in v4:
>>>> 	- New patch
>>>> ---
>>>>  .../devicetree/bindings/watchdog/qcom-wdt.yaml       | 20 ++++++++++++++++++++
>>>>  1 file changed, 20 insertions(+)
>>>>
>>>> diff --git a/Documentation/devicetree/bindings/watchdog/qcom-wdt.yaml b/Documentation/devicetree/bindings/watchdog/qcom-wdt.yaml
>>>> index 49e2b807db0bc9d3edfc93ec41ad0df0b74ed032..bbe9b68ff4c8b813744ffd86bb52303943366fa2 100644
>>>> --- a/Documentation/devicetree/bindings/watchdog/qcom-wdt.yaml
>>>> +++ b/Documentation/devicetree/bindings/watchdog/qcom-wdt.yaml
>>>> @@ -81,6 +81,16 @@ properties:
>>>>      minItems: 1
>>>>      maxItems: 5
>>>>  
>>>> +  qcom,imem:
>>>
>>> Shoouldn't this be existing 'sram' property? If IMEM is something
>>> similar to OCMEM, then we already use sram for that.
>>
>> We specifically want a handle to a predefined byte in IMEM, something akin
>> to qcom,4ln-config-sel in
>>
>> Documentation/devicetree/bindings/phy/qcom,sc8280xp-qmp-pcie-phy.yaml
> 
> Nothing stops that with sram. Above example is poor, because it mentions
> syscon. There is no hardware as syscon. Does not exist. What is IMEM
> here, what is this relationship?

IMEM is indeed a small block of on-die SRAM. In this context, another subsystem
may write a magic value at a known offset that would correspond to the platform
having been rebooted by the watchdog. Now why the wdt register is cleared in the
first place, I have no clue.

Konrad