On Wed, 2012-12-19 at 09:06 +0800, Joseph Lo wrote: > 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@xxxxxxxxxx> 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@xxxxxxxxxx> 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. > > 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. > Hi Colin, I just checked the scenario to abort cpu_pm_enter when there is any pending SGI. This may break the current CPU idle driver that already using cpu_pm_enter. If these drivers didn't handle the error return of "cpu_pm_enter", the error will cause the CPU_PM_ENTER_FAILED be triggered. Then the idle code will fail. The other solution may just like this patch did. Adding an API "gic_pending_sgi" to check if there is a pending SGI before putting the CPU into low power mode. But I still don't think this is a common code to be put there. It's still SoC specific code. So I still prefer the current solution in this patch for Tegra. Thanks, Joseph -- To unsubscribe from this list: send the line "unsubscribe linux-tegra" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
