On Fri, 2012-12-21 at 01:54 +0800, Stephen Warren wrote:

On 12/17/2012 07:31 PM, Joseph Lo wrote:

quoted

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".

quoted

diff --git a/arch/arm/mach-tegra/cpuidle-tegra20.c b/arch/arm/mach-tegra/cpuidle-tegra20.c

quoted

+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.

quoted

@@ -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.

Thanks,
Joseph