Re: [PATCH] ARM: tegra: cpuidle: implement cpuidle_state.enter_freeze()

[Russell King - ARM Linux]

On Fri, May 15, 2015 at 11:03:35AM +0200, Tomeu Vizoso wrote:
> I have been looking and asking around, and seems like we should
> actually leave FIQs enabled when the tick is frozen and only disable
> them within enter_freeze.
> 
> My understanding is that FIQ handlers are extremely limited in what
> they can do, with the main use being NMI-like functionality. There are
> a handful of other FIQ handlers in mainline, but they don't call into
> any other kernel code and limit themselves to doing some basic I/O.
> 
> The only reason why they should be disabled in enter_freeze is that
> the context of the CPU that is going to a lower power state could
> become corrupted if a FIQ gets fired during a save or restore
> operation.

Right, that makes total sense.

(And yes, FIQ handlers are very limited in what they're allowed to do,
since they can't take any locks without the potential for deadlock.)

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