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

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Message-ID: <541866A2.70007@ti.com>
Date:	Tue, 16 Sep 2014 11:34:42 -0500
From:	Nishanth Menon <nm@...com>
To:	<daniel.lezcano@...aro.org>
CC:	Santosh Shilimkar <santosh.shilimkar@...com>,
	Paul Walmsley <paul@...an.com>,
	Tony Lindgren <tony@...mide.com>, Keerthy <j-keerthy@...com>,
	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@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	Kevin Hilman <khilman@...aro.org>,
	linux-pm <linux-pm@...r.kernel.org>
Subject: Re: [PATCH 08/10] ARM: OMAP5/DRA7: PM: cpuidle MPU CSWR support


Daniel,

On 09/05/2014 04:18 PM, Nishanth Menon wrote:
> Daniel,
> 
> On 13:22-20140827, Kevin Hilman wrote:
>> 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.
> 
> 
> Gentle ping.. You can find the discussion and the patch here:
> https://patchwork.kernel.org/patch/4764661/
> 

Ping on this again.. we are pretty close to approaching v3.18 merge
window and this discussion has'nt gotten further.

-- 
Regards,
Nishanth Menon
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