linux-kernel - Re: [PATCH v1 0/6] Introduce power off call chain API

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Date:   Thu, 7 Oct 2021 12:11:06 +0300
From:   Andy Shevchenko <andy.shevchenko@...il.com>
To:     Dmitry Osipenko <digetx@...il.com>
Cc:     Thierry Reding <thierry.reding@...il.com>,
        Jonathan Hunter <jonathanh@...dia.com>,
        Lee Jones <lee.jones@...aro.org>,
        "Rafael J . Wysocki" <rafael@...nel.org>,
        Mark Brown <broonie@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Guenter Roeck <linux@...ck-us.net>,
        Russell King <linux@...linux.org.uk>,
        Daniel Lezcano <daniel.lezcano@...aro.org>,
        Ulf Hansson <ulf.hansson@...aro.org>,
        Linux PM <linux-pm@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-tegra <linux-tegra@...r.kernel.org>
Subject: Re: [PATCH v1 0/6] Introduce power off call chain API

On Thu, Oct 07, 2021 at 11:52:46AM +0300, Dmitry Osipenko wrote:
> 07.10.2021 10:18, Andy Shevchenko пишет:
> > On Thu, Oct 7, 2021 at 9:05 AM Dmitry Osipenko <digetx@...il.com> wrote:

...

> >> This
> >> is a somewhat simplified version which doesn't try to convert whole kernel
> >> to the new API at once, but solves immediate practical problem that we
> > 
> > problems
> > 
> >> have on Nexus 7 Android tablet where device needs to chain power off
> > 
> > tablets where the device
> 
> Thank you for the corrections, so far there is one problem and one tablet :)

Then use "the Nexus 7 Android tablet" :-)

> > Immediate question here is how do you see the plan of spreading this.
> > I.o.w. can you put an explanation that you have checked, let's say
> >> 80% current users, and they may be converted like [example
> > placeholder] without any special tricks?
> 
> The rough plan is:
> 
> 1. Add new API.
> 2. Convert drivers to the new API per subsystem.

I would suggest to show that you are actually into it by converting a couple of
the subsystems for the starter.

> 3. Expose do_kernel_restart().
> 4. Replace pm_power_off() with do_kernel_poweroff() per arch/, making
> power off similar to the restart that uses do_kernel_restart().
> 5. Remove do_kernel_restart() from kernel/reboot.c
> 
> Majority of pm_power_off() users shouldn't need the chaining and
> pm_power_off() doesn't conflict with the new API, so there is no need to
> rush the conversion.
> 
> The single-link chain users could be converted to the new API directly,
> this will remove some global variables. But at first should be better to
> gain more users who actually need the chained power off since they may
> have very specific requirements not covered by the current variant of
> the API and will be easier to evolve API with less users.

All above in one or another form should be in cover letter.

-- 
With Best Regards,
Andy Shevchenko