Message-ID: <20141027171617.GA19379@roeck-us.net>
Date:	Mon, 27 Oct 2014 10:16:17 -0700
From:	Guenter Roeck <linux@...ck-us.net>
To:	Felipe Balbi <balbi@...com>
Cc:	linux-kernel@...r.kernel.org, linux-pm@...r.kernel.org,
	Alan Cox <gnomes@...rguk.ukuu.org.uk>,
	Alexander Graf <agraf@...e.de>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Geert Uytterhoeven <geert@...ux-m68k.org>,
	Heiko Stuebner <heiko@...ech.de>,
	Lee Jones <lee.jones@...aro.org>,
	Len Brown <len.brown@...el.com>, Pavel Machek <pavel@....cz>,
	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	Romain Perier <romain.perier@...il.com>,
	Johan Hovold <johan@...nel.org>
Subject: Re: [PATCH v3 00/47] kernel: Add support for power-off handler call
 chain

On Mon, Oct 27, 2014 at 11:03:24AM -0500, Felipe Balbi wrote:
> Adding Johan, who's working on RTC power off for AM335x devices
> 
Hi Felipe,

is that the rtc-omap driver ?

I am tracking linux-next for related changes. As new power-off handlers are
introduced, I prepare patches for those as well. I currently have patches for
the following two drivers in the queue:
	drivers/regulator/act8865-regulator.c
	drivers/rtc/rtc-omap.c

I plan to send review requests for those patches in a week or so (I think
there is still some change pending to the power-off function in the rtc-omap
driver, and I want to wait for it).

My current plan is to send a pull request for the series directly to Linus
when the next commit window opens; this is what a number of maintainers
suggested I should do. This pull request would exclude the last patch,
so pm_power_off would still be there. Next steps would then be to submit
another set of patches to update the newly introduced power-off handlers
and then to finally remove pm_power_off; this would probably happen after
the commit window closes.

At least that is the plan unless someone has a better idea ....

There may be some variants; for example, it might make sense to create an
immutable branch with the key patches (1-3 and 8) to enable others to use
the new functions immediately. That would require Acks from affected
maintainers for patch 1, though, so I can not do that yet.

Thanks,
Guenter

> On Mon, Oct 27, 2014 at 08:55:07AM -0700, 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 means
> > to remove power is supported (at least if pm_power_off is used).
> > At least in theory there can be multiple means to remove power, some of
> > which may be less desirable.  For example, one mechanism might power off the
> > entire system through an I/O port or gpio pin, while another might power off
> > a board by disabling its power controller. Other mechanisms may really just
> > execute a restart sequence or drop into the ROM monitor, or put the CPU into
> > sleep mode.  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 power-off
> > 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 power-off 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 power-off
> > functionality are expected to register with this call chain.  By using the
> > priority field in the notifier block, callers can control power-off handler
> > execution sequence and thus ensure that the power-off handler with the
> > optimal capabilities to remove power for a given system is called first.
> > A call chain instead of a single call to the highest priority handler is
> > used to provide fallback: If multiple power-off handlers are installed,
> > all handlers will be called until one actually succeeds to power off the
> > system.
> > 
> > Patch 01/47 implements the power-off handler API.
> > 
> > Patches 02/47 to 04/47 are cleanup patches to prepare for the move of
> > pm_power_off to a common location.
> > 
> > Patches 05/47 to 07/47 remove references to pm_power_off from devicetree
> > bindings descriptions.
> > 
> > Patch 08/47 moves the pm_power_off variable from architecture code to
> > kernel/reboot.c. 
> > 
> > Patches 09/47 to 34/47 convert various drivers to register with the kernel
> > power-off handler instead of setting pm_power_off directly.
> > 
> > Patches 35/47 to 46/47 do the same for architecture code.
> > 
> > Patch 47/47 finally removes pm_power_off.
> > 
> > For the most part, the individual patches include explanations why specific
> > priorities were chosen, at least if the selected priority is not the default
> > priority. Subsystem and architecture maintainers are encouraged to have a look
> > at the selected priorities and suggest improvements.
> > 
> > I ran the final code through my normal build and qemu tests. Results are
> > available at http://server.roeck-us.net:8010/builders in the 'poweroff-handler'
> > column. I also built all available configurations for arm, mips, powerpc,
> > m68k, and sh architectures.
> > 
> > The series is available in branch poweroff-handler of my repository at
> > git://git.kernel.org/pub/scm/linux/kernel/git/groeck/linux-staging.git.
> > It is based on 3.18-rc2.
> > 
> > A note on Cc: In the initial submission I had way too many Cc:, causing the
> > patchset to be treated as spam by many mailers and mailing list handlers,
> > which of course defeated the purpose. This time around I am cutting down
> > the distribution list down significantly. My apologies to anyone I may have
> > failed to copy this time around.
> > 
> > Important changes since v2:
> > - Rebased series to v3.18-rc2.
> > - Do not hold any locks while executing the power-off call chain.
> >   This ensures that power-off handlers are executed in the state
> >   selected by the machine_power_off function for a given architecture,
> >   ie without changing the current semantics of power-off callbacks and
> >   machine_power_off functions.
> >   Power-off handler registration and de-registration is handled in atomic
> >   context with interrupts disabled to ensure that those functions are not
> >   interrupted by code which powers off the system.
> > - Use [xxx_]power_off[_xxx] instead of [xxx_]poweroff[_xxx] for newly
> >   introduced function and variable names.
> > - Use power-off instead of poweroff in descriptive text and comments.
> > - Replace POWEROFF_PRIORITY_xxx with POWER_OFF_PRIORITY_xxx
> > - Use ACPI: instead of acpi: for messages in acpi code.
> > 
> > Important changes since v1:
> > - Rebased series to v3.18-rc1.
> > - Use raw notifier with spinlock protection instead of atomic notifiers,
> >   since some power-off handlers need to have interrupts enabled.
> > - Renamed API functions from _poweroff to _power_off.
> > - Added various Acks.
> > - Build tested all configurations for arm, powerpc, and mips architectures.
> > - Fixed two compile errors in mips patch.
> > - Replaced dev_err and pr_err with dev_warn and pr_warn if an error is not
> >   fatal.
> > - Provide managed resources API and use where appropriate.
> > - Provide and use definitions for standard priorities.
> > - Added patches to convert newly introduced power-off handlers.
> > - Various minor changes.
> > 
> > Important changes since RFC:
> > - Move API to new file kernel/power/power_off_handler.c.
> > - Move pm_power_off pointer to kernel/power/power_off_handler.c. Call
> >   pm_power_off from do_kernel_power_off, and only call do_kernel_power_off
> >   from architecture code instead of calling both pm_power_off and
> >   do_kernel_power_off.
> > - Provide additional API function register_power_off_handler_simple
> >   to simplify conversion of architecture code.
> > - Provide additional API function have_kernel_power_off to check if
> >   a power-off handler was installed.
> > - Convert all drivers and architecture code to use the new API.
> > - Remove pm_power_off as last patch of the series.
> > 
> > Cc: Alan Cox <gnomes@...rguk.ukuu.org.uk>
> > Cc: Alexander Graf <agraf@...e.de>
> > Cc: Andrew Morton <akpm@...ux-foundation.org>
> > Cc: Geert Uytterhoeven <geert@...ux-m68k.org>
> > cc: Heiko Stuebner <heiko@...ech.de>
> > Cc: Lee Jones <lee.jones@...aro.org>
> > Cc: Len Brown <len.brown@...el.com>
> > Cc: Pavel Machek <pavel@....cz>
> > Cc: Rafael J. Wysocki <rjw@...ysocki.net>
> > Cc: Romain Perier <romain.perier@...il.com>
> > --
> > To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
> > the body of a message to majordomo@...r.kernel.org
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> > Please read the FAQ at  http://www.tux.org/lkml/
> 
> -- 
> balbi


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