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Date: Tue, 28 Oct 2014 21:58:53 +0100 From: Heiko Stübner <heiko@...ech.de> To: Guenter Roeck <linux@...ck-us.net> 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>, Lee Jones <lee.jones@...aro.org>, Len Brown <len.brown@...el.com>, Pavel Machek <pavel@....cz>, Philippe Rétornaz <philippe.retornaz@...il.com>, "Rafael J. Wysocki" <rjw@...ysocki.net>, Romain Perier <romain.perier@...il.com> Subject: Re: [PATCH v4] kernel: Add support for power-off handler call chain Am Dienstag, 28. Oktober 2014, 10:11:06 schrieb Guenter Roeck: > 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@...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: Philippe Rétornaz <philippe.retornaz@...il.com> > Cc: Rafael J. Wysocki <rjw@...ysocki.net> > Cc: Romain Perier <romain.perier@...il.com> > Signed-off-by: Guenter Roeck <linux@...ck-us.net> > --- Similarly to the restart handlers, I really like the concept. Acked-by: Heiko Stuebner <heiko@...ech.de> -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.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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