linux-kernel - Re: [PATCH 01/44] kernel: Add support for poweroff handler call chain

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Message-ID: <CAH6sp9P7rq2y_hiQPHKUP85CwnEmp87yC7Psh4=29h-pYnb_yw@mail.gmail.com>
Date:	Thu, 18 Jun 2015 08:53:50 +0200
From:	Frans Klaver <fransklaver@...il.com>
To:	Stephen Boyd <sboyd@...eaurora.org>
Cc:	Guenter Roeck <linux@...ck-us.net>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	linux-m32r-ja@...linux-m32r.org, linux-mips@...ux-mips.org,
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	Heiko Stuebner <heiko@...ech.de>, linux-sh@...r.kernel.org,
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	Pavel Machek <pavel@....cz>, devel@...verdev.osuosl.org,
	linux-s390@...r.kernel.org, lguest@...ts.ozlabs.org,
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	Alexander Graf <agraf@...e.de>,
	linux-acpi <linux-acpi@...r.kernel.org>,
	Geert Uytterhoeven <geert@...ux-m68k.org>,
	xen-devel@...ts.xenproject.org, Len Brown <len.brown@...el.com>,
	user-mode-linux-devel@...ts.sourceforge.net,
	"linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
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	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	linux-alpha@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	Romain Perier <romain.perier@...il.com>,
	linuxppc-dev@...ts.ozlabs.org
Subject: Re: [PATCH 01/44] kernel: Add support for poweroff handler call chain

On Thu, Jun 18, 2015 at 3:04 AM, Stephen Boyd <sboyd@...eaurora.org> wrote:
> On 10/06/2014 10:28 PM, Guenter Roeck wrote:
>> Various drivers implement architecture and/or device specific means to
>> remove power from the system.  For the most part, those drivers set the
>> global variable pm_power_off to point to a function within the driver.
>>
>> This mechanism has a number of drawbacks.  Typically only one scheme
>> to remove power is supported (at least if pm_power_off is used).
>> At least in theory there can be multiple means remove power, some of
>> which may be less desirable. For example, some mechanisms may only
>> power off the CPU or the CPU card, while another may power off the
>> entire system.  Others may really just execute a restart sequence
>> or drop into the ROM monitor. Using pm_power_off can also be racy
>> if the function pointer is set from a driver built as module, as the
>> driver may be in the process of being unloaded when pm_power_off is
>> called. If there are multiple poweroff handlers in the system, removing
>> a module with such a handler may inadvertently reset the pointer to
>> pm_power_off to NULL, leaving the system with no means to remove power.
>>
>> Introduce a system poweroff handler call chain to solve the described
>> problems.  This call chain is expected to be executed from the
>> architecture specific machine_power_off() function.  Drivers providing
>> system poweroff functionality are expected to register with this call chain.
>> By using the priority field in the notifier block, callers can control
>> poweroff handler execution sequence and thus ensure that the poweroff
>> handler with the optimal capabilities to remove power for a given system
>> is called first.
>
> What happened to this series? I want to add shutdown support to my
> platform and I need to write a register on the PMIC in one driver to
> configure it for shutdown instead of restart and then write an MMIO
> register to tell the PMIC to actually do the shutdown in another driver.
> It seems that the notifier solves this case for me, albeit with the
> slight complication that I need to order the two with some priority.

I was wondering the same thing. I did find out that things kind of
stalled after Linus cast doubt on the chosen path [1]. I'm not sure
there's any consensus on what would be best to do instead.

Frans

[1] https://lkml.org/lkml/2014/11/6/641
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