Re: [PATCH] ARM: tegra30: fix power up sequence for boot_secondary

[Stephen Warren <swarren-3lzwWm7+Weoh9ZMKESR00Q@public.gmane.org>]

On 12/19/2012 07:30 PM, Joseph Lo wrote:
> The power up sequence is different on the cold boot CPU and the CPU
> that resumed from the hotplug. For the cold boot CPU, it was been power
> gated as default. To power up the cold boot CPU, the power should be
> un-gated by un toggling the power gate register manually.
> 
> For the CPU that resumed from the hotplug, after un-halted the CPU. The
> flow controller will un-gate the power of the CPU. No need to manually
> control, just wait the power be resumed and continue the power up
> sequence after the CPU power is ready.

I'd like Peter to review this too (CC'd). I guess it looks OK...

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

> @@ -72,7 +75,27 @@ static int tegra30_power_up_cpu(unsigned int cpu)
>  	if (pwrgateid < 0)
>  		return pwrgateid;
>  
> -	/* If this is the first boot, toggle powergates directly. */
> +	/*
> +	 * If the CPU had booted and went through here after CPU
> +	 * had been already un-gated by flow controller. Wait
> +	 * for confirmation that the CPU is powered then remove
> +	 * the IO clamps. On the cold boot entry, do not wait.
> +	 */

That comment is quite unclear. In particular the first sentence says "if
something" rather than "if something then something". Can you please
re-write it?

Also, it'd be good to explain (or at least briefly reference) the boot
path for a cold-boot CPU and a warm boot CPU; I assume that somehow a
cold boot CPU doesn't execute tegra_secondary_init(), but a warm boot
CPU does?

> +	if (cpumask_test_cpu(cpu, &tegra_cpu_init_mask)) {
> +		timeout = jiffies + 5;

Are the units/frequency of the jiffies variable always constant? Should
"5" be not a constant, but instead a calculation involving HZ or
msecs_to_jiffies()? Certainly, the few other uses of time_before() I
looked at use HZ or msecs_to_jiffies().