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Date: Wed, 05 Dec 2018 09:09:36 +0900
From: Chanwoo Choi <cw00.choi@...sung.com>
To: Lukasz Luba <l.luba@...tner.samsung.com>,
linux-arm-kernel@...ts.infradead.org,
linux-samsung-soc@...r.kernel.org, linux-kernel@...r.kernel.org,
linux-pm@...r.kernel.org, devicetree@...r.kernel.org
Cc: tjakobi@...h.uni-bielefeld.de, myungjoo.ham@...sung.com,
kyungmin.park@...sung.com, rjw@...ysocki.net, len.brown@...el.com,
pavel@....cz, gregkh@...uxfoundation.org, keescook@...omium.org,
anton@...msg.org, ccross@...roid.com, tony.luck@...el.com,
robh+dt@...nel.org, mark.rutland@....com, kgene@...nel.org,
krzk@...nel.org, m.szyprowski@...sung.com, b.zolnierkie@...sung.com
Subject: Re: [PATCH v2 2/5] devfreq: add support for suspend/resume of a
devfreq device
Hi Lukasz,
On 2018년 12월 04일 18:53, Lukasz Luba wrote:
> Hi Chanwoo,
>
> On 12/4/18 7:10 AM, Chanwoo Choi wrote:
>> Hi Lukasz,
>>
>> I add the comment about 'suspend_count'.
>>
>> On 2018년 12월 04일 14:43, Chanwoo Choi wrote:
>>> Hi,
>>>
>>> On 2018년 12월 04일 14:36, Chanwoo Choi wrote:
>>>> Hi Lukasz,
>>>>
>>>> Looks good to me. But, I add the some comments.
>>>> If you will fix it, feel free to add my tag:
>>>> Reviewed-by: Chanwoo choi <cw00.choi@...sung.com>
>>>
>>> Sorry. Fix typo 'choi' to 'Choi' as following.
>>> Reviewed-by: Chanwoo Choi <cw00.choi@...sung.com>
>>>
>>>>
>>>> On 2018년 12월 03일 23:31, Lukasz Luba wrote:
>>>>> The patch prepares devfreq device for handling suspend/resume
>>>>> functionality. The new fields will store needed information during this
>>>>
>>>> nitpick. Remove unneeded space. There are two spaces between '.' and 'The new'.
>>>>
>>>>> process. Devfreq framework handles opp-suspend DT entry and there is no
>>>>
>>>> ditto.
>>>>
>>>>> need of modyfications in the drivers code. It uses atomic variables to
>>>>
>>>> ditto.
>>>>
>>>>> make sure no race condition affects the process.
>>>>>
>>>>> The patch is based on earlier work by Tobias Jakobi.
>>>>
>>>> Please remove it from each patch description.
>>>>
>>>>>
>>>>> Suggested-by: Tobias Jakobi <tjakobi@...h.uni-bielefeld.de>
>>>>> Suggested-by: Chanwoo Choi <cw00.choi@...sung.com>
>>>>> Signed-off-by: Lukasz Luba <l.luba@...tner.samsung.com>
>>>>> ---
>>>>> drivers/devfreq/devfreq.c | 51 +++++++++++++++++++++++++++++++++++++++--------
>>>>> include/linux/devfreq.h | 7 +++++++
>>>>> 2 files changed, 50 insertions(+), 8 deletions(-)
>>>>>
>>>>> diff --git a/drivers/devfreq/devfreq.c b/drivers/devfreq/devfreq.c
>>>>> index a9fd61b..36bed24 100644
>>>>> --- a/drivers/devfreq/devfreq.c
>>>>> +++ b/drivers/devfreq/devfreq.c
>>>>> @@ -316,6 +316,10 @@ static int devfreq_set_target(struct devfreq *devfreq, unsigned long new_freq,
>>>>> "Couldn't update frequency transition information.\n");
>>>>>
>>>>> devfreq->previous_freq = new_freq;
>>>>> +
>>>>> + if (devfreq->suspend_freq)
>>>>> + devfreq->resume_freq = cur_freq;
>>>>> +
>>>>> return err;
>>>>> }
>>>>>
>>>>> @@ -667,6 +671,9 @@ struct devfreq *devfreq_add_device(struct device *dev,
>>>>> }
>>>>> devfreq->max_freq = devfreq->scaling_max_freq;
>>>>>
>>>>> + devfreq->suspend_freq = dev_pm_opp_get_suspend_opp_freq(dev);
>>>>> + atomic_set(&devfreq->suspend_count, 0);
>>>>> +
>>>>> dev_set_name(&devfreq->dev, "devfreq%d",
>>>>> atomic_inc_return(&devfreq_no));
>>>>> err = device_register(&devfreq->dev);
>>>>> @@ -867,14 +874,28 @@ EXPORT_SYMBOL(devm_devfreq_remove_device);
>>>>> */
>>>>> int devfreq_suspend_device(struct devfreq *devfreq)
>>>>> {
>>>>> + int ret;
>>>>> +
>>>>> if (!devfreq)
>>>>> return -EINVAL;
>>>>>
>>>>> - if (!devfreq->governor)
>>>>> - return 0;
>>>>> + if (devfreq->governor) {
>>>>> + ret = devfreq->governor->event_handler(devfreq,
>>>>> + DEVFREQ_GOV_SUSPEND, NULL);
>>>>> + if (ret)
>>>>> + return ret;
>>>>> + }
>>>>> +
>>>>> + if (devfreq->suspend_freq) {
>>>>> + if (atomic_inc_return(&devfreq->suspend_count) > 1)
>>>>> + return 0;
>>>>> +
>>>>> + ret = devfreq_set_target(devfreq, devfreq->suspend_freq, 0);
>>>>> + if (ret)
>>>>> + return ret;
>>>>> + }
>>
>> In this patch, if some users call 'devfreq_suspend_device' twice,
>> 'devfreq->governor->event_handler(devfreq, DEVFREQ_GOV_SUSPEND, NULL)'
>> is called twice but devfreq_set_target() is called only one.
>> I knew that it is no problem for operation.
>>
>> But,
>> I think that you better to use 'suspend_count' as the reference count
>> of devfreq_suspend/resume_device(). But, if you use 'suspend_count'
>> in order to check whether this devfreq is suspended or not,
>> we can reduce the unneeded redundant call when calling it twice.
>>
>> clock and regulator used the 'reference count' method in order to
>> remove the redundant call.
>
> I think I've got the point. I will move the atomic check just
> after the !devfreq check. Something like the code bellow is what you
> would like to see?
> ---8<-----
> if (!devfreq)
> return -EINVAL;
> if (atomic_inc_return(&devfreq->suspend_count) > 1)
> return0;
Looks good to me. I agree.
>
> ---->8-------
>>
>>
>>>>>
>>>>> - return devfreq->governor->event_handler(devfreq,
>>>>> - DEVFREQ_GOV_SUSPEND, NULL);
>>>>> + return 0;
>>>>> }
>>>>> EXPORT_SYMBOL(devfreq_suspend_device);
>>>>>
>>>>> @@ -888,14 +909,28 @@ EXPORT_SYMBOL(devfreq_suspend_device);
>>>>> */
>>>>> int devfreq_resume_device(struct devfreq *devfreq)
>>>>> {
>>>>> + int ret;
>>>>> +
>>>>> if (!devfreq)
>>>>> return -EINVAL;
>>>>>
>>>>> - if (!devfreq->governor)
>>>>> - return 0;
>>>>> + if (devfreq->resume_freq) {
>>>>> + if (atomic_dec_return(&devfreq->suspend_count) >= 1)
>>>>> + return 0;
>>
>> ditto.
> Same approach here:
> ---8<-----
> if (!devfreq)
> return -EINVAL;
> if (atomic_dec_return(&devfreq->suspend_count) >= 1)
> return 0;
Looks good to me.
> ---->8-------
>
> Regards,
> Lukasz
>>
>>>>>
>>>>> - return devfreq->governor->event_handler(devfreq,
>>>>> - DEVFREQ_GOV_RESUME, NULL);
>>>>> + ret = devfreq_set_target(devfreq, devfreq->resume_freq, 0);
>>>>> + if (ret)
>>>>> + return ret;
>>>>> + }
>>>>> +
>>>>> + if (devfreq->governor) {
>>>>> + ret = devfreq->governor->event_handler(devfreq,
>>>>> + DEVFREQ_GOV_RESUME, NULL);
>>>>> + if (ret)
>>>>> + return ret;
>>>>> + }
>>>>> +
>>>>> + return 0;
>>>>> }
>>>>> EXPORT_SYMBOL(devfreq_resume_device);
>>>>>
>>>>> diff --git a/include/linux/devfreq.h b/include/linux/devfreq.h
>>>>> index e4963b0..d985199 100644
>>>>> --- a/include/linux/devfreq.h
>>>>> +++ b/include/linux/devfreq.h
>>>>> @@ -131,6 +131,9 @@ struct devfreq_dev_profile {
>>>>> * @scaling_min_freq: Limit minimum frequency requested by OPP interface
>>>>> * @scaling_max_freq: Limit maximum frequency requested by OPP interface
>>>>> * @stop_polling: devfreq polling status of a device.
>>>>> + * @suspend_freq: frequency of a device set during suspend phase.
>>>>> + * @resume_freq: frequency of a device set in resume phase.
>>>>> + * @suspend_count: suspend requests counter for a device.
>>>>> * @total_trans: Number of devfreq transitions
>>>>> * @trans_table: Statistics of devfreq transitions
>>>>> * @time_in_state: Statistics of devfreq states
>>>>> @@ -167,6 +170,10 @@ struct devfreq {
>>>>> unsigned long scaling_max_freq;
>>>>> bool stop_polling;
>>>>>
>>>>> + unsigned long suspend_freq;
>>>>> + unsigned long resume_freq;
>>>>> + atomic_t suspend_count;
>>>>> +
>>>>> /* information for device frequency transition */
>>>>> unsigned int total_trans;
>>>>> unsigned int *trans_table;
>>>>>
>>>>
>>>>
>>>
>>>
>>
>>
>
>
--
Best Regards,
Chanwoo Choi
Samsung Electronics
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