linux-kernel - Re: [PATCH v3 4/4] watchdog: qcom: add support to read the restart reason from IMEM

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Message-ID: <1e871aed-705f-4142-b72d-4232ae729a37@oss.qualcomm.com>
Date: Wed, 14 May 2025 18:45:45 +0530
From: Kathiravan Thirumoorthy <kathiravan.thirumoorthy@....qualcomm.com>
To: Konrad Dybcio <konrad.dybcio@....qualcomm.com>,
        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>, bod.linux@...w.ie,
        Srinivas Kandagatla <srini@...nel.org>
Cc: linux-arm-msm@...r.kernel.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-watchdog@...r.kernel.org
Subject: Re: [PATCH v3 4/4] watchdog: qcom: add support to read the restart
 reason from IMEM


On 5/6/2025 4:31 PM, Kathiravan Thirumoorthy wrote:
>
> On 5/3/2025 3:53 AM, Konrad Dybcio wrote:
>> On 5/2/25 6:28 PM, Kathiravan Thirumoorthy wrote:
>>> On 5/2/2025 7:33 PM, Konrad Dybcio wrote:
>>>>> +static int qcom_wdt_get_restart_reason(struct qcom_wdt *wdt,
>>>>> +                    const struct qcom_wdt_match_data *data)
>>>>> +{
>>>>> +    struct regmap *imem;
>>>>> +    unsigned int val;
>>>>> +    int ret;
>>>>> +
>>>>> +    imem = 
>>>>> syscon_regmap_lookup_by_compatible(data->imem_compatible);
>>>> Try syscon_regmap_lookup_by_phandle_args() and pass a phandle, see 
>>>> e.g.
>>>> drivers/phy/qualcomm/phy-qcom-qmp-pcie.c & phy@...c000 in 
>>>> x1e80100.dtsi
>>>>
>>>> That way all platform specifics will live in the DT, requiring no
>>>> hardcode-y driver changes on similar platforms
>>>
>>> Thanks. I thought about this API but it didn't strike that I can use 
>>> the args to fetch and match the value.
>>>
>>> I need a suggestion here. There is a plan to extend this feature to 
>>> other IPQ targets and also support WDIOF_POWERUNDER and 
>>> WDIOF_OVERHEAT cause as well. For IPQ5424, all 3 cause will support 
>>> and for other IPQ platforms, we are exploring how to integrate 
>>> WDIOF_OVERHEAT. In any case, can I define the DT entry like below
>>>
>>>          imem,phandle = <&imem 0x7b0 <Non secure WDT value> <Power 
>>> Under value> <Overheat value>>;
>>>
>>> and store these in values args[1], args[2] and args[3] respectively 
>>> and use it for manipulation? If any of the platform doesn't support 
>>> all 3, I can update the bindings and define the number of args as 
>>> required.
>> Let's call the property qcom,restart-reason and only pass the 
>> register value
>>
>> Because we may have any number of crazy combinations of various restart
>> reasons, we can go two paths:
>>
>> 1. promise really really really hard we won't be too crazy with the 
>> number
>>     of possible values and put them in the driver
>> 2. go all out on DT properties (such as `bootstatus-overheat`,
>> `bootstatus-fanfault` etc.
>
>
> Thanks Konrad for the suggestions and the offline discussions.
>
> @Guenter, I need a suggestion here. Currently as part of this series, 
> we are planning to expose WDIOF_CARDRESET, WDIOF_POWERUNDER, 
> WDIOF_OVERHEAT reasons.
>
> Once this is done, we do have the custom reason codes like Kernel 
> Panic, Secure Watchdog Bite, Bus error timeout, Bus error access and 
> few many. Is it okay to expose these values also via the bootstatus 
> sysFS by extending the current list of reasons? Since these are 
> outside the scope of watchdog, need your thoughts on this.


Konrad / Guenter,

We had a further discussion on this internally. Outcome is, it wouldn't 
be ideal to hook the custom restart reason codes in watchdog framework, 
since there is no involvement of watchdog in such cases. Also I don't 
find any references to hook the custom values in watchdog's bootstatus.

If this is fine, I'm planning to resend the series to handle only the 
non secure watchdog timeout case. In that case, as suggested by Konrad, 
everything will be handled in DT like below to avoid the device data.

imem,phandle = <&phandle <imem_offset> <value>>;

Kindly share your thoughts and inputs on this to proceed further.


>
>
>>
>> I'd much prefer to go with 1 really.. If we used nvmem, we could have 
>> a map
>> of cell names to restart reasons, but we've already established IMEM is
>> volatile and we shouldn't mess up the convention just because that
>> subsystem has nicer APIs..
>>
>> Unless we rename the subsystem to `fuses`, `magic-values` or something..
>> +Srini? :P
>>
>> Konrad