Re: Regarding Devfreq

"Satendra..." <satendra.pratap@xxxxxxxxx> · Wed, 28 Mar 2012 17:41:51 +0530

Hi Ham,
In the below struct :
struct devfreq_dev_status {
        /* both since the last measure */
        unsigned long total_time;
        unsigned long busy_time;
        unsigned long current_frequency;
        void *private_data;
};

How to calculate total_time/busy_time? Does it require hardware support (may be some performance counters)?

Thanks,
Satendra

On 21 March 2012 15:49, 함명주 <myungjoo.ham@xxxxxxxxxxx> wrote:

Hi Stendra,

- Bascially, you can determine the voltage based on frequency; thus, we do not need to determint voltages at DVFS framework. It is corresponding device driver's responsibility even when we have AVS features. Thus, yes, the target callback needs to control both frequency and voltage (and anything else required to change the frequency/voltage)

- I recommend to use regulator framework to control regulators unless you really really need to ignore regulator framework. Don't reinvent the wheel.

- The three steps you've mentioned are correct.

- The mailing list is opened to all. You are welcomed to use it (CC'ed linux-pm) and just CC needed people.

Cheers!
MyungJoo.

------- Original Message -------
Sender : Satendra...<satendra.pratap@xxxxxxxxx>
Date : 2012-03-21 19:03 (GMT+09:00)
Title : Re: Re: Regarding Devfreq

 Hi Ham, 

Thank you very much for your reply. I will try not to disturb you much.
In Devfreq I dont see any API related to voltage scaling. Is it the "->target" function's (in  struct devfreq_dev_profile)
responsibility to change the voltage as well with frequency?
Do we really need to register our regulators using regulator framework of linux for voltage scaling?

For a clear understanding I need to do following to use devfreq (I am sorry as I may be verifying it again):
- define an instance of "struct devfreq_dev_profile" and provide implementations of target, get_dev_status and exit callbacks
- Implement our choice of governer or use any one from already implemented ones.
- call "devfreq_add_device" function from our driver's probe function.

is that it? or do we need to do something else also?

Thanks,
Satendra

On 21 March 2012 15:14, 함명주 <myungjoo.ham@xxxxxxxxxxx> wrote:

Hello Satendra,

- For Devfreq, OPP is optional though recommended for easier implementation. You can still implement all the needed things without OPP. OPP is just a simple data structure to store pairs of voltage and frequency.

- Yes, you need to call devfreq_add_device() and supply the required data. You can implement your own governor or use one of predefined governors. Runtime replacement of governors like CPUfreq is "TODO" for now.

- For example, you can see /drivers/devfreq/exynos4_bus.c. GPU, Display devfreq drivers are under development in other companies (ARM).

Cheers!
MyungJoo.

------- Original Message -------
Sender : Satendra...<satendra.pratap@xxxxxxxxx>
Date : 2012-03-21 17:31 (GMT+09:00)
Title : Re: Regarding Devfreq

 Hi Ham, 

I have studied DVFS and what I feel is that we need to use OPP and Voltage regulator interfaces also to
maintain Optimum Performance Points and to provide APIs to change the voltage.
What I feel is that to use DVFS every driver has to call devfreq_add_device function to register that device to
the devfreq framework. And in order to do that we have to implement devfreq_dev_profile and our choice of governer.

I appreciate your help.

Thanks,
Satendra

On 20 March 2012 12:16, Satendra... <satendra.pratap@xxxxxxxxx> wrote:

Hi Ham, 

We are working on a new SoC for our new product and would want to use your Devfreq
framework for our devices. Would you please let me know any other implementation which
uses devfreq ? so that we could take that as a reference.
Or we would be the first one to start?

Thanks,
Satendra

--
MyungJoo Ham (함명주), PHD
System S/W Lab, S/W Platform Team, Software Center
Samsung Electronics
Cell: +82-10-6714-2858

--
MyungJoo Ham (함명주), PHD
System S/W Lab, S/W Platform Team, Software Center
Samsung Electronics
Cell: +82-10-6714-2858

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