Message-id: <5836B2C2.6090308@samsung.com>
Date:   Thu, 24 Nov 2016 18:28:34 +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 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().

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

>> 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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