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

[Joseph Lo]

On Wed, 2012-12-19 at 03:36 +0800, Colin Cross wrote:
> On Tue, Dec 18, 2012 at 2:15 AM, Peter De Schrijver
> <pdeschrijver at nvidia.com> wrote:
> > 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.
> 
> I'm not sure that is correct for OMAP4.  C2 and C3 will put the power
> rail for the GIC in retention, and I don't think an IPI will wake it
> up.  I believe the same problem also exists for Exynos5.  In any case,
> checking for an IPI early during idle and aborting won't hurt those
> platforms, so I still think it should be in the GIC driver and not by
> mapping the GIC registers into a separate driver.

Hi Colin,

If I move this code into common GIC driver, should I just take care
pending SGI also?

I will try to create a RFC patch for this.

Thanks,
Joseph