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

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Date:   Sun, 28 Nov 2021 01:43:22 +0100
From:   Michał Mirosław <mirq-linux@...e.qmqm.pl>
To:     Dmitry Osipenko <digetx@...il.com>
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>,
        Greg Ungerer <gerg@...ux-m68k.org>,
        Joshua Thompson <funaho@...ai.org>,
        Thomas Bogendoerfer <tsbogend@...ha.franken.de>,
        Sebastian Reichel <sre@...nel.org>,
        Linus Walleij <linus.walleij@...aro.org>,
        Philipp Zabel <p.zabel@...gutronix.de>,
        Greentime Hu <green.hu@...il.com>,
        Vincent Chen <deanbo422@...il.com>,
        "James E.J. Bottomley" <James.Bottomley@...senpartnership.com>,
        Helge Deller <deller@....de>,
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Subject: Re: [PATCH v4 08/25] kernel: Add combined power-off+restart handler
 call chain API

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

Best Regards
Michał Mirosław