linux-kernel - Re: [PATCH v13 07/10] firmware: psci: Implement vendor-specific resets as reboot-mode

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Message-Id: <592902f1-549f-47c5-9ef4-b5c7ef2c9a47@app.fastmail.com>
Date: Wed, 30 Jul 2025 19:31:44 +0200
From: "Arnd Bergmann" <arnd@...db.de>
To: André Draszik <andre.draszik@...aro.org>,
 "Shivendra Pratap" <shivendra.pratap@....qualcomm.com>,
 "Bartosz Golaszewski" <bartosz.golaszewski@...aro.org>,
 "Bjorn Andersson" <andersson@...nel.org>,
 "Sebastian Reichel" <sre@...nel.org>, "Rob Herring" <robh@...nel.org>,
 "Sudeep Holla" <sudeep.holla@....com>,
 "Souvik Chakravarty" <Souvik.Chakravarty@....com>,
 "Krzysztof Kozlowski" <krzk+dt@...nel.org>,
 "Conor Dooley" <conor+dt@...nel.org>, "Andy Yan" <andy.yan@...k-chips.com>,
 "Mark Rutland" <mark.rutland@....com>,
 "Lorenzo Pieralisi" <lpieralisi@...nel.org>,
 "Konrad Dybcio" <konradybcio@...nel.org>,
 cros-qcom-dts-watchers@...omium.org, "Vinod Koul" <vkoul@...nel.org>,
 "Catalin Marinas" <catalin.marinas@....com>, "Will Deacon" <will@...nel.org>,
 "Florian Fainelli" <florian.fainelli@...adcom.com>
Cc: "Dmitry Baryshkov" <dmitry.baryshkov@....qualcomm.com>,
 "Mukesh Ojha" <mukesh.ojha@....qualcomm.com>,
 "Stephen Boyd" <swboyd@...omium.org>, linux-pm@...r.kernel.org,
 linux-kernel@...r.kernel.org, devicetree@...r.kernel.org,
 linux-arm-kernel@...ts.infradead.org, linux-arm-msm@...r.kernel.org,
 "Elliot Berman" <quic_eberman@...cinc.com>,
 "Srinivas Kandagatla" <srini@...nel.org>
Subject: Re: [PATCH v13 07/10] firmware: psci: Implement vendor-specific resets as
 reboot-mode

On Wed, Jul 30, 2025, at 17:23, André Draszik wrote:
> On Wed, 2025-07-30 at 18:33 +0530, Shivendra Pratap wrote:
>> On 7/30/2025 2:14 PM, André Draszik wrote:

>> 1. For this, both commands will be defined in the psci->reboot-mode DT Node with the arguments that
>>    are defined and supported by the firmware.
>> 2. Further, such requirement will now be taken care by the underlying firmware that supports
>>    PSCI vendor-specific reset. When we call into firmware with vendor specific reset arguments,
>>    firmware will take care of the defined HW writes and warm/cold reset as per the mapping of the
>>    defined arguments. Firmware and the Linux kernel here are in agreement for executing the
>>    vendor-specific resets.
>
> So that means
>
>     echo warm > /sys/kernel/reboot/mode
>     reboot bootloader
>
> and
>
>     echo cold > /sys/kernel/reboot/mode
>     reboot bootloader
>
> can not be distinguished.
>
> The firmware can not know whether or not cold or warm reboot was
> requested in this case by the user.

My feeling is that this is fine: the /sys/kernel/reboot/mode
interface is not really used on anything other than 32-bit
arm and x86 machines, and the way it is specific as
cold/warm/hard/soft/gpio is not that useful.

I think for the purpose of the new code here, we should talk
about reboot "commands" instead of "modes" to avoid confusing
between the global "enum reboot_mode" variable and the
firmware interface for reboot modes as listed in DT.

    Arnd