Messages in this thread | | | Date | Tue, 7 Oct 2014 11:39:03 +0100 | From | One Thousand Gnomes <> | Subject | Re: [PATCH 01/44] kernel: Add support for poweroff handler call chain |
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On Mon, 6 Oct 2014 22:28:03 -0700 Guenter Roeck <linux@roeck-us.net> 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.
Nice...
register_poweroff_handler_simple isn't threadsafe. I'm not sure it matters as we should only have one attempt per platform to use it anyway.
have_kernel_poweroff() has a similar problem - the answer isn't always valid by the time the call returns.
The actual poweroff logic is more of a problem - several of the Intel PMICs are on i2c bus, so are not going to be happy in an atomic context so I wonder if that is storing up problems for the future ?
Alan
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