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SubjectRe: [PATCH v3 5/8] PM / devfreq: Get the available next frequency on update_devfreq()
Hi,

On 2017년 10월 11일 22:33, Chanwoo Choi wrote:
> On Wed, Oct 11, 2017 at 8:30 PM, MyungJoo Ham <myungjoo.ham@samsung.com> wrote:
>>> The update_devfreq() considers only user frequency (min_freq/max_freq)
>>> and the next target_freq provided by the governor. But, the commit
>>> a76caf55e5b35 ("thermal: Add devfreq cooling") is able to disable
>>> OPP as a cooling device. In result, the update_devfreq() have to
>>> consider the 'opp->available' status in order to decicde the next freq
>>> by the devfreq_recommended_opp().
>>>
>>> Signed-off-by: Chanwoo Choi <cw00.choi@samsung.com>
>>> ---
>>> drivers/devfreq/devfreq.c | 9 ++++++++-
>>> 1 file changed, 8 insertions(+), 1 deletion(-)
>>>
>>> diff --git a/drivers/devfreq/devfreq.c b/drivers/devfreq/devfreq.c
>>> index 1c4b377cacfb..3b9662ffe603 100644
>>> --- a/drivers/devfreq/devfreq.c
>>> +++ b/drivers/devfreq/devfreq.c
>>> @@ -255,6 +255,7 @@ static int devfreq_notify_transition(struct devfreq *devfreq,
>>> int update_devfreq(struct devfreq *devfreq)
>>> {
>>> struct devfreq_freqs freqs;
>>> + struct dev_pm_opp *opp;
>>> unsigned long freq, cur_freq;
>>> int err = 0;
>>> u32 flags = 0;
>>> @@ -273,7 +274,7 @@ int update_devfreq(struct devfreq *devfreq)
>>> return err;
>>>
>>> /*
>>> - * Adjust the frequency with user freq and QoS.
>>> + * Adjust the frequency with user freq, QoS and available freq.
>>> *
>>> * List from the highest priority
>>> * max_freq
>>> @@ -289,6 +290,12 @@ int update_devfreq(struct devfreq *devfreq)
>>> flags |= DEVFREQ_FLAG_LEAST_UPPER_BOUND; /* Use LUB */
>>> }
>>>
>>> + opp = devfreq_recommended_opp(devfreq->dev.parent, &freq, flags);
>>> + if (IS_ERR(opp))
>>> + return PTR_ERR(opp);
>>> + freq = dev_pm_opp_get_freq(opp);
>>> + dev_pm_opp_put(opp);
>>> +
>>
>> Is this really necessary?
>
> The requirement is due to devfreq_cooling device using
> dev_pm_opp_disable/enable().

I got the better solution. If struct devfreq contains the 'scaling_min/max_freq'
variable, this issue could be fixed. I'll update it with scaling_min/max_freq'
variables on v4.

>
> I added the detailed explanation on cover letter as following:
> If this code is not included, the notifiee using TRANSITION_NOTIFIER
> receives the wrong next target_freq. On the cpufreq, cpufreq doesn't
> use the 'dev_pm_opp_disable/enable()' function and then there is no
> the same issue on cpufreq.
>
> [Cover letter's description about this patch]
> For example,
> - devfreq's min_freq is 100Mhz and max_freq is 700Mhz.
> - OPP disabled 500/600/700Mhz due to devfreq-cooling.c.
> - simple_ondemand govenor decided the next target_freq (600Mhz)
> |----------|-------------------------------------------------------------|
> |Freq(MHz) |100 |200 |300 |400 |500 |600 |70 0 |
> |Devfreq |min_freq| | | | | |max_freq|
> |OPP avail |enabled |enabled|enabled|enabled |Disabled| Disabled|Disabled|
> |Ondmenad | | | | | |next_freq| |
> |------------------------------------------------------------------------|
>
> In result,
> - Before this patch, target_freq is 600Mhz
> and TRANSITION_NOTIFIER sends the next_freq is 600Mhz to the notifiee.
> - After this patch, target_freq is 400Mhz because 500/600 were disabled by OPP.
> and TRANSITION_NOTIFIER sends the next_freq is 400Mhz to the notifiee.
> --------------
>
>>
>> devfreq_recommended_opp is going to be called by the device driver
>> invoked by devfreq->profile->target() function anyway.
>>
>> We are now going to call devfreq_recommended_opp twice in this context.
>>
>>> if (devfreq->profile->get_cur_freq)
>>> devfreq->profile->get_cur_freq(devfreq->dev.parent, &cur_freq);
>>> else
>>> --
>
> Right. The devfreq_recommended_opp() is called twice.
> I wish there was a better way.
>


--
Best Regards,
Chanwoo Choi
Samsung Electronics

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