Re: [PATCH V3 2/5] ARM: tegra20: cpuidle: add powered-down state for secondary CPU

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

On 12/20/2012 11:36 PM, Joseph Lo wrote:
> On Fri, 2012-12-21 at 01:43 +0800, Stephen Warren wrote:
>> On 12/17/2012 07:30 PM, 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

[ code to set up the idle state array]

>> ... although I personally much preferred when all this was just static
>> initialization directly in tegra_idle_driver, rather than all this messy
>> copying. Really, struct cpuidle_driver should point at the array, rather
>> than including it.
>>
> I think so. If you strongly prefer the original style, I can rollback to
> the previous version here.

I suppose there's little point changing it back; I know others objected
to the original code:-(

>>> diff --git a/arch/arm/mach-tegra/pm.c b/arch/arm/mach-tegra/pm.c
>>
>>> @@ -173,6 +173,8 @@ bool __cpuinit tegra_set_cpu_in_lp2(int phy_cpu_id)
>>>  
>>>  	if ((phy_cpu_id == 0) && cpumask_equal(cpu_lp2_mask, cpu_online_mask))
>>>  		last_cpu = true;
>>> +	else if (phy_cpu_id == 1)
>>> +		tegra20_cpu_set_resettable_soon();
>>>  
>>>  	spin_unlock(&tegra_lp2_lock);
>>>  	return last_cpu;
>>
>> Shouldn't the code in that else branch have a run-time check for whether
>> it's running on Tegra20? When compiled without Tegra20 support,
>> tegra20_cpu_set_resettable_soon() is a dummy static inline, but when
>> both Tegra20 and Tegra30 are compiled in, isn't that code going to run
>> when it shouldn't; pm.c being a common file.
>
> Because the code didn't hurt Tegra30, so I didn't add a runtime
> detection there. If you have concern, I can add runtime detection there.

The only issue I see that could happen is that
tegra20_cpu_set_resettable_soon() writes to some location to maintain
the CPU resettable state. Since I assume that location isn't used for
that purpose on Tegra30, could this cause some conflict? It seems best
to add the check to make sure there's no issue here.