Messages in this thread | | | Date | Tue, 28 Oct 2014 13:04:24 -0700 | From | Guenter Roeck <> | Subject | Re: [PATCH v4] kernel: Add support for power-off handler call chain |
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On Tue, Oct 28, 2014 at 07:23:12PM +0100, Pavel Machek wrote: > On Tue 2014-10-28 10:11:06, 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> > > Acked-by: Pavel Machek <pavel@ucw.cz> > Thanks!
Guenter
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