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

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Message-ID: <8a763c70-adcf-4a14-bb68-72ddc61fa045@oss.qualcomm.com>
Date: Sat, 3 May 2025 00:23:56 +0200
From: Konrad Dybcio <konrad.dybcio@....qualcomm.com>
To: Kathiravan Thirumoorthy <kathiravan.thirumoorthy@....qualcomm.com>,
        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 5/2/25 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.

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