Subject: [PATCH 3/7] ARM: tegra30: cpuidle: add LP2 driver for secondary CPUs

From: [email-masked] (Stephen Warren)
Date: Tue, 09 Oct 2012 16:38:02 -0600

On 10/08/2012 04:26 AM, Joseph Lo wrote:
> This supports power-gated (LP2) idle on secondary CPUs for Tegra30.
> The secondary CPUs can go into LP2 state independently. When CPU goes
> into LP2 state, it saves it's state and puts itself to flow controlled
> WFI state. After that, it will been power gated.

> diff --git a/arch/arm/mach-tegra/cpuidle-tegra30.c b/arch/arm/mach-tegra/cpuidle-tegra30.c

>  static struct cpuidle_driver tegra_idle_driver = {
>  	.name = "tegra_idle",
>  	.owner = THIS_MODULE,
>  	.en_core_tk_irqen = 1,
> -	.state_count = 1,
> +	.state_count = 2,

Doesn't that assignment need to be ifdef'd just like the array entry
setup below:

>  	.states = {
>  		[0] = ARM_CPUIDLE_WFI_STATE_PWR(600),
> +#ifdef CONFIG_PM_SLEEP
> +		[1] = {
> +			.enter			= tegra30_idle_lp2,
> +			.exit_latency		= 2000,
> +			.target_residency	= 2200,
> +			.power_usage		= 0,
> +			.flags			= CPUIDLE_FLAG_TIME_VALID,
> +			.name			= "LP2",
> +			.desc			= "CPU power-gate",
> +		},
> +#endif
>  	},
>  };

> @@ -41,6 +114,10 @@ int __init tegra30_cpuidle_init(void)
>  	struct cpuidle_device *dev;
>  	struct cpuidle_driver *drv = &tegra_idle_driver;
>  
> +#ifndef CONFIG_PM_SLEEP
> +	drv->state_count = 1;	/* support clockgating only */
> +#endif

Oh, I see it's done here. Just fixing the static initialization seems a
lot simpler?

> diff --git a/arch/arm/mach-tegra/pm.c b/arch/arm/mach-tegra/pm.c

> +void __cpuinit tegra_clear_cpu_in_lp2(int cpu)
> +{
> +	spin_lock(&tegra_lp2_lock);
> +	BUG_ON(!cpumask_test_cpu(cpu, &tegra_in_lp2));
> +	cpumask_clear_cpu(cpu, &tegra_in_lp2);
> +
> +	/*
> +	 * Update the IRAM copy used by the reset handler. The IRAM copy
> +	 * can't use used directly by cpumask_clear_cpu() because it uses
> +	 * LDREX/STREX which requires the addressed location to be inner
> +	 * cacheable and sharable which IRAM isn't.
> +	 */
> +	writel(tegra_in_lp2.bits[0], tegra_cpu_lp2_mask);
> +	dsb();

Why not /just/ store the data in IRAM, and read/write directly to it,
rather than maintaining an SDRAM-based copy of it?

Then, wouldn't the body of this function be simply:

spin_lock();
BUG_ON(!(tegra_cpu_lp2_mask & BIT(cpu)));
tegra_cpu_lp2_mask |= BIT(cpu);
spin_unlock();

> +bool __cpuinit tegra_set_cpu_in_lp2(int cpu)

Similar comment here.