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

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Message-ID: <46261176-199b-4f6c-ceb4-14646087c814@oss.qualcomm.com>
Date: Mon, 28 Jul 2025 21:38:01 +0530
From: Shivendra Pratap <shivendra.pratap@....qualcomm.com>
To: Dmitry Baryshkov <dmitry.baryshkov@....qualcomm.com>,
        Krzysztof Kozlowski <krzk@...nel.org>
Cc: 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>,
        Arnd Bergmann <arnd@...db.de>, 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>,
        Mukesh Ojha <mukesh.ojha@....qualcomm.com>,
        Stephen Boyd <swboyd@...omium.org>,
        Andre 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>
Subject: Re: [PATCH v13 07/10] firmware: psci: Implement vendor-specific
 resets as reboot-mode



On 7/28/2025 5:33 PM, Dmitry Baryshkov wrote:
> On 28/07/2025 14:52, Krzysztof Kozlowski wrote:
>> On 28/07/2025 11:44, Dmitry Baryshkov wrote:
>>> On Mon, Jul 28, 2025 at 06:53:14AM +0200, Krzysztof Kozlowski wrote:
>>>> On 27/07/2025 18:24, Shivendra Pratap wrote:
>>>>> +
>>>>> +static int __init psci_init_vendor_reset(void)
>>>>> +{
>>>>> +    struct reboot_mode_driver *reboot;
>>>>> +    struct device_node *np;
>>>>> +    int ret;
>>>>> +
>>>>> +    np = of_find_node_by_path("/psci/reboot-mode");
>>>>
>>>>
>>>> Why are you looking by full path, not by compatible? Is the ABI - above
>>>> path - expressed anywhere?
>>>
>>> PSCI node is required to have a node name of psci, it doesn't have MMIO,
>>
>> This is true
>>
>>> so it resides in the root node
>>
>> This might be or not might be true. It is not defined by ABI. Anyway,
>> you answered where the ABI would be documented, even though as I said it
>> is not (/psci is not), but does not answer to first part: why you are
>> not using compatibles which is always the preferred method?
> 
> That's a good question, I've added one from my side: why do we need an extra late_init call.
"psci" registers with reboot-mode which creates a class and a device under it for exposing
the sysfs.
psci_dt_init is called very early around setup_kernel. At that stage the class creating fails,
so psci cannot register with reboot-mode at this stage.
At early_init, the class creation is success, but the created class and the sysfs does not
enumerates under /sys/class/.
So i added explicit late_init call for this where the sysfs creation seems to work fine.
> 
>>
>>
>>> and the reboot-mode is defined in the
>>> previous patch. So, I'd assume, the path is defined.
>>
>> As I said, path is not. only psci/reboot-mode is.
> 
> Do we have an _actual_ use case where PSCI node is not at at root node? If not, it's obviously a deficiency of the schema. Could you please provide suggestions on how to describe that in DT schema?
> 
>