Messages in this thread | | | Date | Thu, 6 Nov 2014 14:27:03 -0800 | From | Guenter Roeck <> | Subject | Re: [PATCH v5 01/48] kernel: Add support for power-off handler call chain |
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On Thu, Nov 06, 2014 at 11:30:59PM +0100, Rafael J. Wysocki wrote: > On Thursday, November 06, 2014 08:42:45 AM Guenter Roeck wrote: > > Various drivers implement architecture and/or device specific means to > > power off 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 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 and architeceture code > > providing system power-off functionality are expected to register with > > this call chain. When registering a power-off handler, callers can > > provide a priority to 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. > > > > Cc: Alan Cox <gnomes@lxorguk.ukuu.org.uk> > > Cc: Alexander Graf <agraf@suse.de> > > Cc: Andrew Morton <akpm@linux-foundation.org> > > Cc: Geert Uytterhoeven <geert@linux-m68k.org> > > Cc: Heiko Stuebner <heiko@sntech.de> > > Cc: Lee Jones <lee.jones@linaro.org> > > Cc: Len Brown <len.brown@intel.com> > > Cc: Pavel Machek <pavel@ucw.cz> > > Cc: Philippe Rétornaz <philippe.retornaz@gmail.com> > > Cc: Rafael J. Wysocki <rjw@rjwysocki.net> > > Cc: Romain Perier <romain.perier@gmail.com> > > Acked-by: Pavel Machek <pavel@ucw.cz> > > Acked-by: Heiko Stuebner <heiko@sntech.de> > > Signed-off-by: Guenter Roeck <linux@roeck-us.net> > > --- > > v5: > > - Rebase to v3.18-rc3 > > v4: > > - Do not use notifiers but internal functions and data structures to manage > > the list of power-off handlers. Drop unused parameters from callbacks, and > > make the power-off function type void. > > Code to manage and walk the list of callbacks is derived from notifier.c. > > v3: > > - Rename new file to power_off_handler.c > > - Replace poweroff in all newly introduced variables and in text > > with power_off or power-off as appropriate > > - Replace POWEROFF_PRIORITY_xxx with POWER_OFF_PRIORITY_xxx > > - Execute power-off handlers without any locks held > > v2: > > - poweroff -> power_off > > - Add defines for default priorities > > - Use raw notifiers protected by spinlocks instead of atomic notifiers > > - Add register_poweroff_handler_simple > > - Add devm_register_power_off_handler > > > > include/linux/pm.h | 28 ++++ > > kernel/power/Makefile | 1 + > > kernel/power/power_off_handler.c | 293 +++++++++++++++++++++++++++++++++++++++ > > 3 files changed, 322 insertions(+) > > create mode 100644 kernel/power/power_off_handler.c > > > > diff --git a/include/linux/pm.h b/include/linux/pm.h > > index 383fd68..a4d6bf8 100644 > > --- a/include/linux/pm.h > > +++ b/include/linux/pm.h > > @@ -35,6 +35,34 @@ extern void (*pm_power_off)(void); > > extern void (*pm_power_off_prepare)(void); > > > > struct device; /* we have a circular dep with device.h */ > > + > > +/* > > + * Data structures and callbacks to manage power-off handlers > > + */ > > + > > +struct power_off_handler_block { > > + void (*handler)(struct power_off_handler_block *); > > + struct power_off_handler_block __rcu *next; > > + int priority; > > +}; > > + > > +int register_power_off_handler(struct power_off_handler_block *); > > +int devm_register_power_off_handler(struct device *, > > + struct power_off_handler_block *); > > +int register_power_off_handler_simple(void (*function)(void), int priority); > > +int unregister_power_off_handler(struct power_off_handler_block *); > > +void do_kernel_power_off(void); > > +bool have_kernel_power_off(void); > > + > > +/* > > + * Pre-defined power-off handler priorities > > + */ > > +#define POWER_OFF_PRIORITY_FALLBACK 0 > > +#define POWER_OFF_PRIORITY_LOW 64 > > +#define POWER_OFF_PRIORITY_DEFAULT 128 > > +#define POWER_OFF_PRIORITY_HIGH 192 > > +#define POWER_OFF_PRIORITY_HIGHEST 255 > > I'm not sure why we need these gaps in the priority space. > > I guess it might be possible to use > > enum power_off_priority { > POWER_OFF_PRIORITY_FALLBACK = 0, > POWER_OFF_PRIORITY_LOW, > POWER_OFF_PRIORITY_DEFAULT, > POWER_OFF_PRIORITY_HIGH, > POWER_OFF_PRIORITY_HIGHEST, > POWER_OFF_PRIORITY_LIMIT, > };
I retained the large number space on purpose, specifically to permit in-between priorities. In other words, I want people to be able to say "priority for this handler is higher than low but lower than default". After all, the defines were intended as hints, not as a "Thou shall use those and only those priorities".
Having said that, the important part is to get the series accepted, so I won't argue if that is what it takes to get an Ack. Let me know.
Thanks, Guenter
> > and then make register_ complain if priority is POWER_OFF_PRIORITY_LIMIT > or greater. > > But I'm OK with the rest, so if no one else sees a problem here, > I'm not going to make a fuss about it. > > Rafael > -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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