Subject: [PATCH V2 2/6] ARM: tegra20: cpuidle: add powered-down state for secondary CPU

From: [email-masked] (Stephen Warren)
Date: Wed, 05 Dec 2012 15:18:14 -0700

On 12/05/2012 03:01 AM, Joseph Lo wrote:
> 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. The Tegra20 had a limition to
> power down both CPU cores. The secondary CPU must waits for CPU0 in
> powered-down state too. If the secondary CPU be woken up before CPU0
> entering powered-down state, then it needs to restore its CPU states
> and waits for next chance.
> 
> 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 int __cpuinit tegra20_idle_lp2(struct cpuidle_device *dev,

> +	return (entered_lp2) ? index : 0;

No need for the brackets there.

BTW, could you Cc Colin Cross on any future revisions of these patches;
it'd be good to get his take on them.

> diff --git a/arch/arm/mach-tegra/sleep-tegra20.S b/arch/arm/mach-tegra/sleep-tegra20.S

> +/*
> + * tegra_pen_lock

> + * on cpu 0:
> + * SCRATCH38 = r2 = flag[0]
> + * SCRATCH39 = r3 = flag[1]

It would be slightly clearer if that was written:

* r2 = flag[0] (in SCRATCH38)
* r3 = flag[1] (in SCRATCH39)

since the meaning of r2/r3 is what's being selected.

> +	mov	r12, #1
> +	str	r12, [r2]		@ flag[cpu] = 1
> +	dsb
> +	str	r12, [r1]		@ !turn = cpu

Should that be "str r0, [r1]"? Otherwise, you're always writing 1 there,
not writing the CPU ID as expected.