[PATCH V3 1/5] ARM: tegra: add pending SGI checking API

[Peter De Schrijver]

On Tue, Dec 18, 2012 at 03:42:24AM +0100, Colin Cross wrote:
> On Mon, Dec 17, 2012 at 6:30 PM, Joseph Lo <josephl at nvidia.com> wrote:
> > The "powered-down" CPU idle mode of Tegra cut off the vdd_cpu rail, it
> > include the power of GIC. That caused the SGI (Software Generated
> > Interrupt) been lost. Because the SGI can't wake up the CPU that in
> > the "powered-down" CPU idle mode. We need to check if there is any
> > pending SGI when go into "powered-down" CPU idle mode. This is important
> > especially when applying the coupled cpuidle framework into "power-down"
> > cpuidle dirver. Because the coupled cpuidle framework may have the
> > chance that misses IPI_SINGLE_FUNC handling sometimes.
> 
> This problem exists for any GIC-based SoC, and needs to be fixed in
> gic_cpu_save or gic_dist_save, whichever one loses the interrupt.

Not necessarily. It depends on the SoC design. On Tegra20, the entire CPU
cluster is railgated, including the GIC. This causes a pending IPI to be lost.
But for example on OMAP4, only the actual CPU cores are powergated. The GIC
stays alive until also the core domain hits idle. By that time a potential
pending IPI has long woken up the target CPU again, so no additional
checks are needed for functional correct behavior.

Cheers,

Peter.