[PATCH] ARM:CPUIDLE: Fix wrongly used idle control counter

On Thu, Sep 27, 2012 at 02:19:49AM -0700, Fan Wu wrote:

Thanks a lot for reviewing. 

So, you mean it is driver's responsibility to make sure the "disable
and enable" function are paired before using it, which I think is
NOT OK for current code. 

It is, and always has been.

1. If we want different users have chance to sync about the counter, 
	I think we may try the following ways
		1). add one interface (like exported function) for other
	 modules or driver to get the current counter value .

That is broken.

		2). add constraint in "enable and disable" function to
	 avoid the possible situation that the counter is
	 less/more than "0".

Err what?

2. If we want the "nohlt" is OK for every driver and module without
sync or similar operation,
	We may just remove "enable and disable" interface directly,
which will cause the "nohlt" change will only be the init interface
and cannot be changed any more after kernel bootup.

WTF.

No.  Look, it is _VERY_ simple.

Drivers must _not_ call enable_hlt() without first having called
disable_hlt() - and the number of enable_hlt()s must _NEVER_ be more
than the number of times you've called disable_hlt().

That's exactly the same with other subsystems - eg, you must not call
enable_irq() without having first called disable_irq(), and you must
not call enable_irq() more times than you've called disable_irq().

It is senseless to export the nohlt count - doing so will _create_ bugs
because if a driver were to ever use this value (which is a cumulative
value) then it can call enable_hlt() more times than it's called
disable_hlt() because of the interaction with another driver.

When drivers comply with the interface, the "nohlt" command line argument
works - it calls disable_hlt() once without a following enable_hlt(),
which means that hlt (or rather, putting the CPU into a low power mode)
is disabled at boot time and never enabled.

So, if you have a driver which is calling enable_hlt() without first
having called disable_hlt(), fix that driver.  There is nothing wrong
in the generic ARM code, and the generic ARM code can't help you work
around the broken driver.