From mboxrd@z Thu Jan 1 00:00:00 1970 From: santosh.shilimkar@ti.com (Santosh Shilimkar) Date: Sat, 12 Jan 2013 12:20:01 +0530 Subject: [PATCH 08/16] ARM: bL_platsmp.c: make sure the GIC interface of a dying CPU is disabled In-Reply-To: References: <1357777251-13541-1-git-send-email-nicolas.pitre@linaro.org> <1357777251-13541-9-git-send-email-nicolas.pitre@linaro.org> <50F054E7.9000004@ti.com> Message-ID: <50F10799.3000501@ti.com> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org On Saturday 12 January 2013 12:37 AM, Nicolas Pitre wrote: > On Fri, 11 Jan 2013, Santosh Shilimkar wrote: > >> On Thursday 10 January 2013 05:50 AM, Nicolas Pitre wrote: >>> Otherwise there might be some interrupts or IPIs becoming pending and the >>> CPU will not enter low power mode when doing a WFI. The effect of this >>> is a CPU that loops back into the kernel, go through the first man >>> election, signals itself as alive, and prevent the cluster from being >>> shut down. >>> >>> This could benefit from a better solution. >>> >>> Signed-off-by: Nicolas Pitre >>> --- >>> arch/arm/common/bL_platsmp.c | 1 + >>> arch/arm/common/gic.c | 6 ++++++ >>> arch/arm/include/asm/hardware/gic.h | 2 ++ >>> 3 files changed, 9 insertions(+) >>> >>> diff --git a/arch/arm/common/bL_platsmp.c b/arch/arm/common/bL_platsmp.c >>> index 0ae44123bf..6a3b251b97 100644 >>> --- a/arch/arm/common/bL_platsmp.c >>> +++ b/arch/arm/common/bL_platsmp.c >>> @@ -68,6 +68,7 @@ static void __ref bL_cpu_die(unsigned int cpu) >>> pcpu = mpidr & 0xff; >>> pcluster = (mpidr >> 8) & 0xff; >>> bL_set_entry_vector(pcpu, pcluster, NULL); >>> + gic_cpu_if_down(); >> >> So for a case where CPU still don't power down for some reason even >> after CPU interface is disabled, can not listen to and SGI or PPI. >> Not sure if this happens on big.LITTLE but i have seen one such issue >> on Cortex-A9 based SOC. > > Here the problem was the reverse i.e. a CPU wouldn't go down because > some pending SGIs prevented that. > I understood that part. What I was saying is, with CPU IF disabled and if CPU doesn't enter into the intended low power state and if the wakeup mechanism on that CPU is SGI/SPI, CPU may never wakeup and can lead to dead lock. I have seen this scenario on OMAP especially in CPUidle path. It may not be relevant for switcher considering, you almost force CPU to enter to low power state :-) Regards, Santosh