Messages in this thread | | | Date | Tue, 7 Oct 2014 08:51:05 -0700 | From | Guenter Roeck <> | Subject | Re: [PATCH 01/44] kernel: Add support for poweroff handler call chain |
| |
On Tue, Oct 07, 2014 at 11:39:03AM +0100, One Thousand Gnomes wrote: > 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. > Yes, I know. Agreed, it should not matter, but maybe it can be solved by using raw notifiers and spinlocks for protection.
> have_kernel_poweroff() has a similar problem - the answer isn't always > valid by the time the call returns. > This is an interesting one. Logically the answer can not be guaranteed to be correct by the time it is evaluated in the calling code, no matter how much protection I add around it. Not sure if there is anything I can or should do about that.
> 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 ? > Yes, Philippe brought that up as well. I think I may have to use raw notifiers, and use spinlocks for protection. Would this work ?
Thanks, Guenter
| |