linux-kernel - Re: [PATCH RFC 0/6] Add support to read the restart reason from IMEM

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Message-ID: <07426a13-7897-4fe8-bfc4-549730717e85@oss.qualcomm.com>
Date: Wed, 9 Apr 2025 20:49:36 +0200
From: Konrad Dybcio <konrad.dybcio@....qualcomm.com>
To: Kathiravan Thirumoorthy <kathiravan.thirumoorthy@....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>
Cc: linux-arm-msm@...r.kernel.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-watchdog@...r.kernel.org
Subject: Re: [PATCH RFC 0/6] Add support to read the restart reason from IMEM

On 4/8/25 10:49 AM, Kathiravan Thirumoorthy wrote:
> In Qualcomm IPQ SoC, if the system is rebooted due to the watchdog
> timeout, there is no way to identify it. Current approach of checking
> the EXPIRED_STATUS in WDT_STS is not working.
> 
> To achieve this, if the system is rebooted due to watchdog timeout, the
> information is captured in the IMEM by the bootloader (along with other
> reason codes as well).
> 
> This series attempts to address this by adding the support to read the
> IMEM and populate the information via bootstatus sysfs file. As of now,
> we are handling only the non secure watchdog timeout reason.
> 
> Signed-off-by: Kathiravan Thirumoorthy <kathiravan.thirumoorthy@....qualcomm.com>
> ---

So I think it would be easier to model this as nvram (something like
"nvmem-rmem" with imem perhaps modeled as "mmio-sram") and then consume
that value through in-kernel APIs (or write to it, as necessary)

Taking a quick look at mobile, it seems like "reboot bootloader" and
friends use a similar mechanism

Konrad