Message-id: <5836B8D1.9050707@samsung.com>
Date:   Thu, 24 Nov 2016 18:54:25 +0900
From:   Chanwoo Choi <cw00.choi@...sung.com>
To:     hl <hl@...k-chips.com>, myungjoo.ham@...sung.com
Cc:     "linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
        "dbasehore@...omium.org" <dbasehore@...omium.org>,
        "dianders@...omium.org" <dianders@...omium.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-rockchip@...ts.infradead.org" 
        <linux-rockchip@...ts.infradead.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        Tobias Jakobi <tjakobi@...h.uni-bielefeld.de>
Subject: Re: [PATCH v1 & v6 1/2] PM/devfreq: add suspend frequency support

Hi Lin,

On 2016년 11월 24일 18:28, Chanwoo Choi wrote:
> Hi Lin,
> 
> On 2016년 11월 24일 17:34, hl wrote:
>> Hi Chanwoo Choi,
>>
>>
>> On 2016年11月24日 16:16, Chanwoo Choi wrote:
>>> Hi Lin,
>>>
>>> On 2016년 11월 24일 16:34, hl wrote:
>>>> Hi Chanwoo Choi,
>>>>
>>>>      I think the dev_pm_opp_get_suspend_opp() have implement most of
>>>> the funtion, all we need is just define the node in dts, like following:
>>>>
>>>> &dmc_opp_table {
>>>>      opp06 {
>>>>          opp-suspend;
>>>>      };
>>>> };
>>> Two approaches use the 'opp-suspend' property.
>>>
>>> I think that the method to support suspend-opp have to
>>> guarantee following conditions:
>>> - Support the all of devfreq's governors.
>>     As MyungJoo Ham suggestion, i will set the suspend frequency in devfreq_suspend_device(),
>> which will ingore governor.
> 
> Other approach already support the all of governors.
> Before calling the mail, I discussed with Myungjoo Ham.
> Myungjoo prefer to use the devfreq_suspend/devfreq_resume().

It is not correct expression. We need to wait the reply from Myungjoo
to clarify this.

> 
> To Myungjoo,
> Please add your opinion how to support the suspend frequency.

> 
>>> - Devfreq framework have the responsibility to change the
>>>    frequency/voltage for suspend-opp. If we uses the
>>>    new devfreq_suspend(), each devfreq device don't care
>>>    how to support the suspend-opp. Just the developer of each
>>>    devfreq device need to add 'opp-suspend' propet to OPP entry in DT file.
>> Why should support change the voltage in devfreq framework, i think it shuold be handle in
>> specific driver, i think the devfreq only handle it can get the right frequency, then pass it to
> 
> No, the frequency should be handled by governor or framework. 
> The each devfreq device has no any responsibility of next frequency/voltage.
> The governor and core of devfreq can decide the next frequency/voltage.
> You can refer to the cpufreq subsystem.
> 
>> specific driver, i think the voltage should handle in the devfreq->profile->target();
> 
> The call of devfreq->profile->target() have to be handled by devfreq framework.
> If user want to set the suspend frequency, user can add the 'suspend-opp' property.
> It think this way is easy. 
> 
> But,
> If the each devfreq device want to decide the next frequency/voltage only for
> suspend state. We can check the cpufreq subsystem.
> 
> If specific devfreq device want to handle the suspend frequency,
> each devfreq will add the own suspend/resume functions as following:
> 
> 	struct devfreq_dev_profile {
> 		int (*suspend)(struct devfreq *dev);	// new function pointer	
> 		int (*resume)(struct devfreq *dev);	// new function pointer
> 	} a_profile;
> 
> 	a_profile = devfreq_generic_suspend;
> 
> 	The devfreq framework will provide the devfreq_generic_suspend() funticon.
> 		int devfreq_generic_suspend(struce devfreq *dev) {
> 			...
> 			devfreq->profile->target(..., devfreq->suspend_freq);
> 			...
> 		}	
> 
> 	or
> 
> 	a_profile = a_devfreq_suspend; // specific function of each devfreq device
> 
> 	The devfreq_suspend() will call 'devfreq->profile->suspend()' function
> 	instead of devfreq->profile->target(); 
> 
> 	The devfreq call the 'devfreq->profile->suspend()'
> 	to support the suspend frequency.
> 
> Regards,
> Chanwoo Choi

The key difference between two approaches:

Your approach:
- The each developer should add the 'opp-suspend' property to the dts file.
- The each devfreq should call the devfreq_suspend_device()
  to support the suspend frequency.

  If each devfreq doesn't call the devfreq_suspend_device(), devfreq framework
  can support the suspend frequency.

Other approach:
- The each developer only should add the 'opp-suspend' property to the dts file
  without the additional behavior.

In the cpufreq subsystem,
When support the suspend frequency of cpufreq, we just add 'opp-suspend' property
without the additional behavior.

Regards,
Chanwoo Choi

> 
>>> Best Regards,
>>> Chanwoo Choi
>>>
>>>> so i think my way semm more simple.
>>>>
>>>> On 2016年11月24日 15:10, Chanwoo Choi wrote:
>>>>> + Tobias Jakobi,
>>>>>
>>>>> Hi Lin,
>>>>>
>>>>> We need to discuss how to support the suspend-opp of devfreq device.
>>>>> Now, there are two patch thread for suspend-opp of devfreq.
>>>>>
>>>>> The Lin's approach modify the devfreq_suspend_device() to support suspend-opp.
>>>>> The Tobias's approach[1] add new devfreq_suspend() and then call it on dpm_suspend()
>>>>> when entering the suspend state.
>>>>>
>>>>> [1] [RFC 0/4] PM / devfreq: draft for OPP suspend impl
>>>>> - https://patchwork.kernel.org/patch/9443323/
>>>>> - https://patchwork.kernel.org/patch/9443325/
>>>>> - https://patchwork.kernel.org/patch/9443329/
>>>>> - https://patchwork.kernel.org/patch/9443331/
>>>>>
>>>>> I think we need to discuss it together.
>>>>>
>>>>> Regards,
>>>>> Chanwoo Choi
>>>>>
>>>>> On 2016년 11월 24일 15:45, hl wrote:
>>>>>> Hi MyungJoo Ham,
>>>>>>
>>>>>> On 2016年11月24日 14:14, MyungJoo Ham wrote:
>>>>>>> On Thu, Nov 24, 2016 at 11:18 AM, hl <hl@...k-chips.com> wrote:
>>>>>>>> Hi MyungJoo Ham,
>>>>>>> []
>>>>>>>>> We still need to sync the all status even i call target() in
>>>>>>>>> devfreq_suspend/resume_device
>>>>>>>>> directly, so still need update_devfreq() other setp except
>>>>>>>>> devfreq->governor->get_target_freq(devfreq, &freq);
>>>>>>>> And i think it better to be governor behaviors, for userspace they may not
>>>>>>>> want to change
>>>>>>>> the suspend frequency like other governor, the frequency should decide by
>>>>>>>> the user, if they
>>>>>>>> want this function, they should like other governor to rigister a
>>>>>>>> devfreq_monitor_suspend().
>>>>>>>> What do you think about my rev6 patch?
>>>>>>> If I understand the intention correctly, this is for the stability of
>>>>>>> the device due to the behavior or bootloader/SoC-initializer, which
>>>>>>> has nothing to do with governors.
>>>>>>>
>>>>>>> Even if users are using userspace, as long as they set the custom
>>>>>>> frequencies lower than the default, they have the possibility of
>>>>>>> being unstable as ondemand is going to have.
>>>>>>>
>>>>>>>
>>>>>>> To reuse the update_devfreq() code, you may do something like:
>>>>>>>
>>>>>>> static int _update_freq(struct devfreq *devfreq, bool is_suspending)
>>>>>>> {
>>>>>>>       /* original contents of update_freq with if statement with is_suspending wrapping get_target_freq */
>>>>>>> }
>>>>>>> int update_freq(struct devfreq *devfreq)
>>>>>>> {
>>>>>>>      return _update_freq(devfreq, false);
>>>>>>> }
>>>>>>>
>>>>>>>
>>>>>>> There should be other good non-invasive methods that are not governoe-specific as well.
>>>>>>>
>>>>>> Thanks for your suggestion, i will update the new version soon.
>>>>>>> Cheers,
>>>>>>> MyungJoo
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>> _______________________________________________
>>>>>>> Linux-rockchip mailing list
>>>>>>> Linux-rockchip@...ts.infradead.org
>>>>>>> http://lists.infradead.org/mailman/listinfo/linux-rockchip
>>>>>> -- 
>>>>>> Lin Huang
>>>>>>
>>>>>
>>>>>
>>>
>>>
>>>
>>
> 
> 


-- 
Best Regards,
Chanwoo Choi

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