[PATCH 4/7] ARM: EXYNOS4: Support early wakeup while entering sleep mode

[Kukjin Kim]

Russell King - ARM Linux wrote:
> >
> > Hi Russell and all,
> >
> > I'd like to share requirement of EXYNOS4210 PM.
> >
> > Now if there is wakeup source which is pending before entering suspend
mode,
> > PMU(Power Management Unit) handles WFI instruction as NOP on EXYNOS4210.
> But
> > it seems that current cpu_suspend() cannot support this. So how
can/should
> > we handle this case?
> 
> See patch from June 13th posted to the hibernate thread.  This allows
> the finisher function to return, though it should only return if it is
> certain that the system will not enter suspend.
> 
> Is this true of the current exynos4 code?  It seems that the current
> code will panic() if the WFI is executed as a NOP.
> 
Yes, you're right, current code cannot control it. Supporting this case will
be scheduled in next patch.

> > And this is another case. For example, assume that ARM is power down
mode
> > and outer cache(L2 cache) data is retention state to use L2 cache data
after
> > wakeup. In this case, according to wakeup sequence, firstly L1 cache is
> > enabled in cpu_resume() then L2 cache will be enabled which is
implemented
> > in Samsung SoC specific code. So how can be handled the coherency
problem
> > between L1 cache and L2 cache?
> 
> You could ensure that L2 is ready to be re-enabled before calling
> cpu_resume.  As the C bit in the control register will be cleared,
> L2 should not be used at that point, until after the MMU is re-
> initialized.

Russell, thanks for your kindly explanation :)

Best regards,
Kgene.
--
Kukjin Kim <kgene.kim at samsung.com>, Senior Engineer,
SW Solution Development Team, Samsung Electronics Co., Ltd.