Re: [PATCH] MIPS: switch BMIPS5000 to use r4k_wait_irqoff()

[Ralf Baechle <ralf@linux-mips.org>]

On Tue, Jan 12, 2016 at 12:42:14AM +0000, Maciej W. Rozycki wrote:

> > > Programming notes:
> > > The WAIT instruction should be executed while interrupts are disabled
> > > by the IE bit in the Status register. This avoids a potential timing
> > > hazard, which occurs if an interrupt is taken between testing the counter
> > > and executing the WAIT instruction. In this hazard case, the interrupt
> > > will have been completed before the WAIT instruction is executed, so
> > > the processor will remain indefinitely in wait state until the next
> > > interrupt.
> > 
> > Note that this is the opposite restriction than many older MIPS CPUs
> > where it is undefined if an interrupt will restart execution of
> > instructions if interrupts are disabled.  So this might be a violation
> > of the architecture specification.  However I rather have it the BMIPS
> > way than the other way ...
> 
>  It's been implementation-dependent since MIPSr1 whether a non-enabled 
> interrupt breaks out of WAIT, so no architecture specification violation 
> here.

I probably should have clarified that in the commit message but alas
too late, this commit is long upstream.

  Ralf