Messages in this thread |  | | Date | Tue, 21 Oct 2014 06:17:09 -0700 | From | Guenter Roeck <> | Subject | Re: [PATCH v2 01/47] kernel: Add support for poweroff handler call chain |
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On 10/21/2014 05:26 AM, Rafael J. Wysocki wrote: > On Monday, October 20, 2014 09:12:17 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. > > Well, I must admit to having second thoughts regarding this particular > mechanism. Namely, notifiers don't seem to be the best way of expressing > what's needed from the design standpoint. > > It looks like we need a list of power off methods and a way to select one > of them, so it seems that using a plist would be a natural choice here? > Isn't a notifier call chain nothing but a list of methods, with its priority the means to select which one to use (first) ?
The only difference I can see is that you would only select one of them, meaning the one with the highest priority, and not try the others. Am I missing something ?
Thanks, Guenter
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