linux-kernel - Re: [PATCH v12 0/8] Implement vendor resets for PSCI SYSTEM

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Message-Id: <fd153e95-b06d-47f9-b079-566908c20df2@app.fastmail.com>
Date: Thu, 24 Jul 2025 22:14:52 +0200
From: "Arnd Bergmann" <arnd@...db.de>
To: "Shivendra Pratap" <shivendra.pratap@....qualcomm.com>,
 "Krzysztof Kozlowski" <krzk@...nel.org>,
 "Florian Fainelli" <florian.fainelli@...adcom.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>
Cc: "Dmitry Baryshkov" <dmitry.baryshkov@....qualcomm.com>,
 "Mukesh Ojha" <mukesh.ojha@....qualcomm.com>,
 "Stephen Boyd" <swboyd@...omium.org>,
 André Draszik <andre.draszik@...aro.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>,
 "Elliot Berman" <elliot.berman@....qualcomm.com>,
 "Konrad Dybcio" <konrad.dybcio@....qualcomm.com>
Subject: Re: [PATCH v12 0/8] Implement vendor resets for PSCI SYSTEM_RESET2

On Thu, Jul 24, 2025, at 20:21, Shivendra Pratap wrote:
> On 7/24/2025 8:13 PM, Arnd Bergmann wrote:
>> On Thu, Jul 24, 2025, at 16:04, Shivendra Pratap wrote:
>> How about using the reboot driver name as the identifier in sysfs
>> instead of the compatible string? That would make it independent of
>> devicetree.
> In current patch, psci driver registers to reboot-mode using a device-tree
> node. So reboot-mode does not has a driver name for psci's reboot registration.
> its like -  reboot_mode_register(reboot, <struct device_node *np>)
>
> Now when we want to use the registering reboot driver's name for sysfs,
> either we- 
> 1, Pass an explicit name from psci driver(say "psci") while registering
> to reboot-mode.
> or
> 2. Create a virtual device in psci driver with name say "psci" and then
> register for reboot-mode.
>
> which one is preferred? suggestions? 

I would pick 1, to decouple the namespace from the device and to
keep it simpler.

>> I had a related idea to provide some namespacing on the actual
>> reboot syscall parameter, as we have two (or more) orthogonal
>> concepts here, when there is more than one reboot driver and
>> drivers support multiple modes.
>> 
>> E.g. you could use
>> 
>>     syscall(__NR_reboot, LINUX_REBOOT_MAGIC1, LINUX_REBOOT_MAGIC2, 
>>             LINUX_REBOOT_CMD_RESTART2, "watchdog");
>> 
>> vs
>> 
>>     syscall(__NR_reboot, LINUX_REBOOT_MAGIC1, LINUX_REBOOT_MAGIC2, 
>>             LINUX_REBOOT_CMD_RESTART2, "psci");
>> 
>> to pick one of the drivers, or
>> 
>>     syscall(__NR_reboot, LINUX_REBOOT_MAGIC1, LINUX_REBOOT_MAGIC2, 
>>             LINUX_REBOOT_CMD_RESTART2, "bootloader");
>> 
>>     syscall(__NR_reboot, LINUX_REBOOT_MAGIC1, LINUX_REBOOT_MAGIC2, 
>>             LINUX_REBOOT_CMD_RESTART2, "recovery");
>> 
>> to ask for a reboot from any driver that supports a mode, or
>> combine the two and ask a specific mode in a specific driver like
>> 
>>     syscall(__NR_reboot, LINUX_REBOOT_MAGIC1, LINUX_REBOOT_MAGIC2, 
>>             LINUX_REBOOT_CMD_RESTART2, "psci:bootloader");
> This will introduce an additional feature in the reboot-mode driver.
> If a colon is present in the command like "<driver name>:bootloader",
> Call the "<driver name>" specific writes only. 
> We want to add this feature? 

I think this will require a little more rework in the reboot
infrastructure, and I did not mean for you to do it now, we
can always decide to do this as a follow-up, but I brought it
up because the way we pick the namespace will limit our options
later.

      Arnd