Re: [patch 07/15] clocksource: Provide unbind interface in sysfs

[John Stultz]

On 04/25/2013 01:31 PM, Thomas Gleixner wrote:
> With the module refcount held for the current clocksource there is no
> way to unload the module.
>
> Provide a sysfs interface which allows to unbind the clocksource. One
> could argue that the clocksource override could be (ab)used to do so,
> but the clocksource override cannot be used from the kernel itself,
> while an unbind function can be used to programmatically check whether
> a clocksource can be shutdown or not.
>
> The unbind functionality uses the new skip current feature of
> clocksource_select and verifies that a fallback clocksource has been
> installed. If the clocksource which should be unbound is the current
> clocksource and no fallback can be found, unbind returns -EBUSY.
>
> This does not support the unbinding of a clocksource which is used as
> the watchdog clocksource. No point in fostering crappy hardware.

So.. if the clocksource you want to unbind is the highest rated 
continuous clocksource that doesn't need a watchdog (basically what's 
likely to be in-use and required to be unbinded), its likely to be 
selected as the watchdog already.

ie: on a system that has only HPET/ACPI_PM, you can't unbind HPET, since 
its a watchdog.

Or are you really wanting to prohibit this functionality for all 
CONFIG_CLOCKSOURCE_WATCHDOG hardware, which would be easier to do via 
build time ifdefs?

thanks
-john

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