linux-kernel - Re: [PATCH 08/10] ARM: OMAP5/DRA7: PM: cpuidle MPU CSWR support

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Date:	Wed, 27 Aug 2014 13:22:43 -0700
From:	Kevin Hilman <khilman@...aro.org>
To:	Santosh Shilimkar <santosh.shilimkar@...com>
Cc:	Nishanth Menon <nm@...com>, Paul Walmsley <paul@...an.com>,
	Tony Lindgren <tony@...mide.com>, Keerthy <j-keerthy@...com>,
	<daniel.lezcano@...aro.org>, lkml <linux-kernel@...r.kernel.org>,
	Tero Kristo <t-kristo@...com>,
	Benoît Cousson <bcousson@...libre.com>,
	linux-omap <linux-omap@...r.kernel.org>,
	"linux-arm-kernel\@lists.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH 08/10] ARM: OMAP5/DRA7: PM: cpuidle MPU CSWR support

Santosh Shilimkar <santosh.shilimkar@...com> writes:

> On Wednesday 27 August 2014 03:35 PM, Nishanth Menon wrote:
>> On Wed, Aug 27, 2014 at 2:13 PM, Kevin Hilman
>> <khilman@...prootsystems.com> 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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