linux-kernel - Re: [PATCH v4 08/25] kernel: Add combined power-off+restart handler call chain API

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Message-ID: <9213569e-0f40-0df1-4710-8dab564e12d6@gmail.com>
Date:   Mon, 29 Nov 2021 00:04:01 +0300
From:   Dmitry Osipenko <digetx@...il.com>
To:     Michał Mirosław <mirq-linux@...e.qmqm.pl>
Cc:     Thierry Reding <thierry.reding@...il.com>,
        Jonathan Hunter <jonathanh@...dia.com>,
        Russell King <linux@...linux.org.uk>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>, Guo Ren <guoren@...nel.org>,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
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Subject: Re: [PATCH v4 08/25] kernel: Add combined power-off+restart handler
 call chain API

28.11.2021 03:43, Michał Mirosław пишет:
> On Fri, Nov 26, 2021 at 09:00:44PM +0300, Dmitry Osipenko wrote:
>> SoC platforms often have multiple ways of how to perform system's
>> power-off and restart operations. Meanwhile today's kernel is limited to
>> a single option. Add combined power-off+restart handler call chain API,
>> which is inspired by the restart API. The new API provides both power-off
>> and restart functionality.
>>
>> The old pm_power_off method will be kept around till all users are
>> converted to the new API.
>>
>> Current restart API will be replaced by the new unified API since
>> new API is its superset. The restart functionality of the sys-off handler
>> API is built upon the existing restart-notifier APIs.
>>
>> In order to ease conversion to the new API, convenient helpers are added
>> for the common use-cases. They will reduce amount of boilerplate code and
>> remove global variables. These helpers preserve old behaviour for cases
>> where only one power-off handler is expected, this is what all existing
>> drivers want, and thus, they could be easily converted to the new API.
>> Users of the new API should explicitly enable power-off chaining by
>> setting corresponding flag of the power_handler structure.
> [...]
> 
> Hi,
> 
> A general question: do we really need three distinct chains for this?

Hello Michał,

At minimum this makes code easier to follow.

> Can't there be only one that chain of callbacks that get a stage
> (RESTART_PREPARE, RESTART, POWER_OFF_PREPARE, POWER_OFF) and can ignore
> them at will? Calling through POWER_OFF_PREPARE would also return
> whether that POWER_OFF is possible (for kernel_can_power_off()).

I'm having trouble with parsing this comment. Could you please try to
rephrase it? I don't see how you could check whether power-off handler
is available if you'll mix all handlers together.

> I would also split this patch into preparation cleanups (like wrapping
> pm_power_off call with a function) and adding the notifier-based
> implementation.

What's the benefit of this split up will be? Are you suggesting that it
will ease reviewing of this patch or something else?