On 12/21/2012 12:10 AM, Joseph Lo wrote: > On Fri, 2012-12-21 at 01:54 +0800, Stephen Warren wrote: >> On 12/17/2012 07:31 PM, Joseph Lo wrote: >>> The "powered-down" cpuidle mode of Tegra20 needs the CPU0 be the last one >>> core to go into this mode before other core. The coupled cpuidle framework >>> can help to sync the MPCore to coupled state then go into "powered-down" >>> idle mode together. The driver can just assume the MPCore come into >>> "powered-down" mode at the same time. No need to take care if the CPU_0 >>> goes into this mode along and only can put it into safe idle mode (WFI). >>> >>> The powered-down state of Tegra20 requires power gating both CPU cores. >>> When the secondary CPU requests to enter powered-down state, it saves >>> its own contexts and then enters WFI for waiting CPU0 in the same state. >>> When the CPU0 requests powered-down state, it attempts to put the secondary >>> CPU into reset to prevent it from waking up. Then power down both CPUs >>> together and power off the cpu rail. >>> >>> Be aware of that, you may see the legacy power state "LP2" in the code >>> which is exactly the same meaning of "CPU power down". >> >>> diff --git a/arch/arm/mach-tegra/cpuidle-tegra20.c b/arch/arm/mach-tegra/cpuidle-tegra20.c >> >>> +static void tegra20_wake_reset_cpu_1(void) >> >> Nit/bikeshe: I think tegra20_wake_from_reset_cpu_1() might be a slightly >> more descriptive name? I assume the function works on CPU1, which is >> assumed to be in reset, and removes reset from the CPU so it boots. >> > Yes. > Do you mean this function running on CPU1? It runs on CPU0 to wake up > CPU1. About the function name, it looks more appropriate. Sorry for bikeshedding even more, perhaps tegra20_wake_cpu_1_from_reset(); that makes the word-order better English. >>> @@ -137,6 +241,9 @@ int __init tegra20_cpuidle_init(void) >>> for_each_possible_cpu(cpu) { >>> dev = &per_cpu(tegra_idle_device, cpu); >>> dev->cpu = cpu; >>> +#ifdef CONFIG_ARCH_NEEDS_CPU_IDLE_COUPLED >>> + dev->coupled_cpus = *cpu_online_mask; >>> +#endif >> >> That CONFIG option is selected by ARCH_TEGRA_2x_SOC, which must be >> enabled for this file to be compiled. So, you can drop the ifdef, and >> make the code uncondtional. > > No, I found I need this if I want to make the device works on UP case. > Then I need to do something like below, when we disable SMP. > >> config ARCH_TEGRA_2x_SOC >> bool "Enable support for Tegra20 family" >> + select ARCH_NEEDS_CPU_IDLE_COUPLED if SMP >> select ARCH_REQUIRE_GPIOLIB >> select ARM_ERRATA_720789 >> select ARM_ERRATA_742230 > > This will be updated in next version as well. OK, if the Kconfig looks like that, you're right - the ifdef in the .c file is needed. -- 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