linux-kernel - Re: [PATCH v7 04/20] kernel: Add combined power-off+restart handler call chain API

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Message-ID: <f8075f97-4cc7-b802-97af-c0ef5a969624@collabora.com>
Date:   Fri, 6 May 2022 17:46:57 +0300
From:   Dmitry Osipenko <dmitry.osipenko@...labora.com>
To:     "Rafael J. Wysocki" <rafael@...nel.org>
Cc:     Thierry Reding <thierry.reding@...il.com>,
        Jonathan Hunter <jonathanh@...dia.com>,
        Russell King <linux@...linux.org.uk>,
        Catalin Marinas <catalin.marinas@....com>,
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Subject: Re: [PATCH v7 04/20] kernel: Add combined power-off+restart handler
 call chain API

On 4/20/22 21:47, Rafael J. Wysocki wrote:
>>>> +/**
>>>> + *     devm_register_prioritized_power_off_handler - Register prioritized power-off callback
>>>> + *     @dev: Device that registers callback
>>>> + *     @priority: Callback's priority
>>>> + *     @callback: Callback function
>>>> + *     @cb_data: Callback's argument
>>>> + *
>>>> + *     Registers resource-managed power-off callback with a given priority.
>>>> + *     It will be called as last step of the power-off sequence. Callbacks
>>>> + *     chaining is disabled, i.e. further lower priority callbacks won't
>>>> + *     be executed if this @callback will fail to execute.
>>>> + *
>>>> + *     Returns zero on success, or error code on failure.
>>> What's the case in which this should be used instead of registering a
>>> full sys_off handler?
>> There are a lot of drivers that just want to register power-off handler
>> with a non-default priority and don't need to stop the chain or do
>> anything else special. This is a convinient helper for them.
>>
>> Please note that the callback here takes only the cb_data for the
>> argument, while sys_off uses "struct power_off_data".
>>
>> Similar for the reset of the convinient helpers.
> So if there is a way to do this, why would anyone prefer to use the
> full sys_off handler at all?

There are couple occurrences around kernel where there is no device
available for the devm_ functions, like this for example [1].

[1]
https://gitlab.collabora.com/dmitry.osipenko/linux-kernel-rd/-/commit/184dfd3983e774d3cf9050dc5b4ec23a662a9551

-- 
Best regards,
Dmitry