linux-kernel - Re: [PATCH 1/3] PM / devfreq: set min/max freq limit from freq table

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Date:	Mon, 4 Feb 2013 14:03:36 +0530
From:	Rajagopal Venkat <rajagopal.venkat@...aro.org>
To:	myungjoo.ham@...il.com
Cc:	kyungmin.park@...sung.com, mturquette@...aro.org, rjw@...k.pl,
	patches@...aro.org, linaro-dev@...ts.linaro.org,
	linux-pm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/3] PM / devfreq: set min/max freq limit from freq table

MyungJoo, Ping.

On 15 January 2013 16:51, Rajagopal Venkat <rajagopal.venkat@...aro.org> wrote:
> On 14 January 2013 20:06, MyungJoo Ham <myungjoo.ham@...sung.com> wrote:
>> On Tue, Jan 8, 2013 at 2:50 PM, Rajagopal Venkat
>> <rajagopal.venkat@...aro.org> wrote:
>>> Set devfreq device min and max frequency limits when device
>>> is added to devfreq, provided frequency table is supplied.
>>> This helps governors to suggest target frequency with in
>>> limits.
>>>
>>> Signed-off-by: Rajagopal Venkat <rajagopal.venkat@...aro.org>
>>
>> Could you please elaborate the benefit of the patch?
>>
>
> When freq table is supplied, it's unreasonable to suggest the target frequency
> which is - target_freq < min_freq and target_freq > max_freq. It avoids
> unnecessary checks at devfreq drivers.
>
>> The devfreq device drivers are required to choose proper frequencies
>> anyway regardless which values the governors may give (hopefully by
>> choosing the closest value that can support the required performance).
>>
>
> Yes. but then each driver needs to have conditional checks for choosing
> closet value even though freq table is provided.
>
>> Besides, the min/max values are to be set by userspace. Users may
>> enter 0 in order to express that they do not want to limit the
>> behaviors of governors.
>>
>>
>> Cheers,
>> MyungJoo.
>>
>>> ---
>>>  drivers/devfreq/devfreq.c |   24 ++++++++++++++++++++++++
>>>  1 file changed, 24 insertions(+)
>>>
>>> diff --git a/drivers/devfreq/devfreq.c b/drivers/devfreq/devfreq.c
>>> index a8f0173..5782c9b 100644
>>> --- a/drivers/devfreq/devfreq.c
>>> +++ b/drivers/devfreq/devfreq.c
>>> @@ -69,6 +69,29 @@ static struct devfreq *find_device_devfreq(struct device *dev)
>>>  }
>>>
>>>  /**
>>> + * devfreq_set_freq_limits() - Set min and max frequency from freq_table
>>> + * @devfreq:   the devfreq instance
>>> + */
>>> +static void devfreq_set_freq_limits(struct devfreq *devfreq)
>>> +{
>>> +       int idx;
>>> +       unsigned long min = ~0, max = 0;
>>> +
>>> +       if (!devfreq->profile->freq_table)
>>> +               return;
>>> +
>>> +       for (idx = 0; idx < devfreq->profile->max_state; idx++) {
>>> +               if (min > devfreq->profile->freq_table[idx])
>>> +                       min = devfreq->profile->freq_table[idx];
>>> +               if (max < devfreq->profile->freq_table[idx])
>>> +                       max = devfreq->profile->freq_table[idx];
>>> +       }
>>> +
>>> +       devfreq->min_freq = min;
>>> +       devfreq->max_freq = max;
>>> +}
>>> +
>>> +/**
>>>   * devfreq_get_freq_level() - Lookup freq_table for the frequency
>>>   * @devfreq:   the devfreq instance
>>>   * @freq:      the target frequency
>>> @@ -476,6 +499,7 @@ struct devfreq *devfreq_add_device(struct device *dev,
>>>                                                 devfreq->profile->max_state,
>>>                                                 GFP_KERNEL);
>>>         devfreq->last_stat_updated = jiffies;
>>> +       devfreq_set_freq_limits(devfreq);
>>>
>>>         dev_set_name(&devfreq->dev, dev_name(dev));
>>>         err = device_register(&devfreq->dev);
>>> --
>>> 1.7.10.4
>>>
>>> --
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>>
>>
>>
>> --
>> MyungJoo Ham, Ph.D.
>> Mobile Software Platform Lab, DMC Business, Samsung Electronics
>
>
>
> --
> Regards,
> Rajagopal



-- 
Regards,
Rajagopal
--
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