Santosh Shilimkar <santosh.shilimkar@xxxxxx> writes:
> On Wednesday 27 August 2014 03:35 PM, Nishanth Menon wrote:
>> On Wed, Aug 27, 2014 at 2:13 PM, Kevin Hilman
>> <khilman@xxxxxxxxxxxxxxxxxxx> wrote:
>>> + Daniel (cpuidle maintainer)
>> [...]
>>>> +static int omap_enter_idle_smp(struct cpuidle_device *dev,
>>>> + struct cpuidle_driver *drv,
>>>> + int index)
>>>> +{
>>>> + struct idle_statedata *cx = state_ptr + index;
>>>> + unsigned long flag;
>>>> +
>>>> + raw_spin_lock_irqsave(&mpu_lock, flag);
>>>> + cx->mpu_state_vote++;
>>>> + if (cx->mpu_state_vote == num_online_cpus()) {
>>>> + pwrdm_set_logic_retst(mpu_pd, cx->mpu_logic_state);
>>>> + omap_set_pwrdm_state(mpu_pd, cx->mpu_state);
>>>> + }
>>>> + raw_spin_unlock_irqrestore(&mpu_lock, flag);
>>>> +
>>>> + omap4_enter_lowpower(dev->cpu, cx->cpu_state);
>>>> +
>>>> + raw_spin_lock_irqsave(&mpu_lock, flag);
>>>> + if (cx->mpu_state_vote == num_online_cpus())
>>>> + omap_set_pwrdm_state(mpu_pd, PWRDM_POWER_ON);
>>>> + cx->mpu_state_vote--;
>>>> + raw_spin_unlock_irqrestore(&mpu_lock, flag);
>>>> +
>>>> + return index;
>>>> +}
>>>
>>> Hmm, maybe OMAP5/DRA7 CPUidle driver should be a new one based on MCPM?
>>
>> Trying to understand benefit of MCPM here - at least without a deeper
>> understanding of mcpm infrastructure benefits (first look seemed a
>> little heavy for OMAP5/DRA7 needs).
>>
>> Neither DRA7/OMAP5 are multi-cluster, the SoCs are not targetted for
>> "OFF" of CPU1/0, we have mercury hardware to help with context and
>> sync issues.
>>
>> Being able to reuse most of existing OMAP4 infrastructure code is
>> useful as well to leave the existing omap4 framework as being lighter
>> in complexity -esp in a cpuidle like hot path?
>>
>> The spin_lock is only for the programming of MPU power domain in a
>> consistent manner - I suppose might have been the trigger for
>> proposing mcpm?
>>
> Mostly not....
>
> I think this is coming because last time Nicolas Pitre tried to convert
> the OMAP CPUIdle into MCPM but because of various ordering requirements,
> OMAP wasn't suitable and then the plan was dropped later.
>
> Just to make clear, OMAP OMAP5/DRA7 as well the ordering requirement
> remains the same for deeper states. Its just the mercury retention state
> which we are able to enter without ordering requirements and hence
> the voting scheme.
Ah, OK. This is the part that I'm missing. So for deeper states you'll
need to be using omap_enter_idle_coupled()
> Hope this clarifies to you as well as Kevin just in case he missed the
> part of the deeper C-states requirements.
Yes, thanks for clarifying.
That being said, I think MCPM can now do essentially what the coupled
states code is doing. Even so, that's probably not a reason to hold up
this patch, but Daniel gets to make that call.
Kevin
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