[PATCH v7 00/11] kernel: Add support for restart handler call chain

[Heiko Stübner]

Am Samstag, 23. August 2014, 09:35:05 schrieb Guenter Roeck:
> On Tue, Aug 19, 2014 at 05:45:27PM -0700, Guenter Roeck wrote:
> > Various drivers implement architecture and/or device specific means
> > to restart (reset) the system. Various mechanisms have been implemented
> > to support those schemes. The best known mechanism is arm_pm_restart,
> > which is a function pointer to be set either from platform specific code
> > or from drivers. Another mechanism is to use hardware watchdogs to issue
> > a reset; this mechanism is used if there is no other method available
> > to reset a board or system. Two examples are alim7101_wdt, which currently
> > uses the reboot notifier to trigger a reset, and moxart_wdt, which
> > registers the arm_pm_restart function. Several other restart drivers for
> > arm, all directly calling arm_pm_restart, are in the process of being
> > integrated into the kernel. All those drivers would benefit from the new
> > API.
> > 
> > The existing mechanisms have a number of drawbacks. Typically only one
> > scheme to restart the system is supported (at least if arm_pm_restart is
> > used). At least in theory there can be multiple means to restart the
> > system, some of which may be less desirable (for example one mechanism
> > may only reset the CPU, while another may reset the entire system). Using
> > arm_pm_restart can also be racy if the function pointer is set from a
> > driver, as the driver may be in the process of being unloaded when
> > arm_pm_restart is called.
> > Using the reboot notifier is always racy, as it is unknown if and when
> > other functions using the reboot notifier have completed execution
> > by the time the watchdog fires.
> > 
> > Introduce a system restart handler call chain to solve the described
> > problems. This call chain is expected to be executed from the
> > architecture specific machine_restart() function. Drivers providing
> > system restart functionality (such as the watchdog drivers mentioned
> > above) are expected to register with this call chain. By using the
> > priority field in the notifier block, callers can control restart handler
> > execution sequence and thus ensure that the restart handler with the
> > optimal restart capabilities for a given system is called first.
> > 
> > Since the first revision of this patchset, a number of separate patch
> > submissions have been made which either depend on it or could make use of
> > it.
> > 
> > http://www.spinics.net/linux/lists/arm-kernel/msg344796.html
> > 
> > 	registers three notifiers.
> > 
> > https://lkml.org/lkml/2014/7/8/962
> > 
> > 	would benefit from it.
> > 
> > Patch 1 of this series implements the restart handler function. Patches 2
> > and 3 implement calling the restart handler chain from arm and arm64
> > restart code.
> > 
> > Patch 4 modifies the restart-poweroff driver to no longer call
> > arm_pm_restart directly but machine_restart. This is done to avoid
> > calling arm_pm_restart from more than one place. The change makes the
> > driver architecture independent, so it would be possible to drop the arm
> > dependency from its Kconfig entry.
> > 
> > Patch 5 and 6 convert existing restart handlers in the watchdog subsystem
> > to use the restart handler. Patch 7 unexports arm_pm_restart to ensure
> > that no one gets the idea to implement a restart handler as module.
> > 
> > The entire patch series, including additional patches depending on it,
> > is available from
> > https://git.kernel.org/cgit/linux/kernel/git/groeck/linux-staging.git/
> > in branch 'restart-staging'.
> 
> Hi Andrew,
> 
> I think this series is ready for upstream integration. Question now
> is how we should proceed to get it actually integrated.
> 
> I can see a number of options:
> - You take patch #1, the rest goes in through maintainer trees.

I don't think you can split the patches like this. Patch1 introduces 
(un)register_restart_handler functions used by later patches in the series. 
You therefore cannot really split the series, as otherwise you would get build 
failures in the individual trees.


Heiko


> - You take all patches after we get missing maintainer Acks.
> - I send a pull request directly to Linus after we get missing
>   maintainer Acks.
> 
> What do you think would be the best way to proceed ?
> 
> Thanks,
> Guenter