On Thu, Jun 18, 2015 at 1:54 PM, Guenter Roeck <linux@xxxxxxxxxxxx> wrote: > On 06/17/2015 11:53 PM, Frans Klaver wrote: >> >> On Thu, Jun 18, 2015 at 3:04 AM, Stephen Boyd <sboyd@xxxxxxxxxxxxxx> >> 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. >> > > Linus cast doubt on it, then the maintainers started picking it apart. > At the end, trying not to use notifier callbacks made the code so > complicated that even I didn't understand it anymore. With no consensus > in sight, I abandoned it. > > Problem is really that the notifier call chain would be perfect to solve > the problem, yet Linus didn't like priorities (which are essential), > and the power maintainers didn't like that a call chain is supposed > to execute _all_ callbacks, which would not be the case here. If I were > to start again, I would insist to use notifiers. However, I don't see > a chance to get that accepted, so I won't. Feel free to pick it up and > give it a try yourself. How about having two phases? One where all interested parts of the system get notified, one that does the final shutdown. It's a slightly different approach than you took, but does use the notifier chains as expected, and can be used to prepare peripherals for shutdown, if there's a use case for it. The two-stage approach does keep the single place to power down. I expect it would become more obvious that it would be silly to have more than one actual system power down sequence and hiding pm_power_off and unifying setting of it should become more straight forward as well. Thoughts? Thanks, Frans
