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Date: Mon, 26 Nov 2018 09:19:35 +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 3/6] devfreq: add support for suspend/resume of a
devfreq device
Hi Lukasz,
I add the one more comment for devfreq_resume_device()
On 2018년 11월 23일 19:01, Lukasz Luba wrote:
> Hi Chanwoo Choi,
>
> On 11/23/18 12:54 AM, Chanwoo Choi wrote:
>> Hi Lukasz,
>>
>> I add one more comment about devfreq_resume_device().
>>
>> On 2018년 11월 22일 20:00, Lukasz Luba wrote:
>>>
>>>
>>> On 11/22/18 3:58 AM, Chanwoo Choi wrote:
>>>> On 2018년 11월 22일 03:01, Lukasz Luba wrote:
>>>>> The patch adds support for handling suspend/resume process.
>>>>> It uses atomic variables to make sure no race condition
>>>>> affects the process.
>>>>>
>>>>> The patch draws on Tobias Jakobi's work posted ~2 years ago, who tried to
>>>>> solve issue with devfreq device's frequency during suspend/resume.
>>>>> During the discussion on LKML some corner cases and comments appeared
>>>>> related to the design. This patch address them keeping in mind suggestions
>>>>> from Chanwoo Choi.
>>>>
>>>> Please remove the duplicate information about patch history.
>>>>
>>>>>
>>>>> 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 | 45 +++++++++++++++++++++++++++++++++++++++------
>>>>> 1 file changed, 39 insertions(+), 6 deletions(-)
>>>>>
>>>>> diff --git a/drivers/devfreq/devfreq.c b/drivers/devfreq/devfreq.c
>>>>> index cf9c643..7e09de8 100644
>>>>> --- a/drivers/devfreq/devfreq.c
>>>>> +++ b/drivers/devfreq/devfreq.c
>>>>> @@ -872,14 +872,33 @@ EXPORT_SYMBOL(devm_devfreq_remove_device);
>>>>> */
>>>>> int devfreq_suspend_device(struct devfreq *devfreq)
>>>>> {
>>>>> - if (!devfreq)
>>>>> - return -EINVAL;
>>>>> + int ret;
>>>>
>>>> Move 'ret' definition under 'if (devfreq->suspend_freq) {'
>>>> because 'ret' is used if suspend_freq isn't zero.
>>> Not only there, 6 lines above 'ret' is used for
>>> devfreq->governor->event_handler().
>>
>> OK.
>>
>>>>
>>>>> + unsigned long prev_freq;
>>>>> + u32 flags = 0;
>>>>> +
>>>>> + if (!devfreq)
>>>>> + return -EINVAL;
>>>>> +
>>>>> + if (devfreq->governor) {
>>>>> + ret = devfreq->governor->event_handler(devfreq,
>>>>> + DEVFREQ_GOV_SUSPEND, NULL);
>>>>> + if (ret)
>>>>> + return ret;
>>>>> + }
>>>>>
>>>>> - if (!devfreq->governor)
>>>>> - return 0;
>>>>> + if (devfreq->suspend_freq) {
>>>>> + if (atomic_inc_return(&devfreq->suspend_count) > 1)
>>>>> + return 0;
>>>>>
>>>>> - return devfreq->governor->event_handler(devfreq,
>>>>> - DEVFREQ_GOV_SUSPEND, NULL);
>>>>> + ret = devfreq_set_target(devfreq, devfreq->suspend_freq,
>>>>> + &prev_freq, flags);
>>>>
>>>> Remove the 'prev_freq' parameter.
>>> OK
>>>>
>>>>> + if (ret)
>>>>> + return ret;
>>>>> +
>>>>> + devfreq->resume_freq = prev_freq;
>>>>
>>>> As I commented on patch2, if devfreq_set_taget save the current frequency
>>>> to 'devfreq->resume_freq', this line is not needed.
>>> OK
>>>>
>>>>
>>>>> + }
>>>>> +
>>>>> + return 0;
>>>>> }
>>>>> EXPORT_SYMBOL(devfreq_suspend_device);
>>>>>
>>>>> @@ -893,9 +912,23 @@ EXPORT_SYMBOL(devfreq_suspend_device);
>>>>> */
>>>>> int devfreq_resume_device(struct devfreq *devfreq)
>>>>> {
>>>>> + int ret;
>>>>
>>>> Move 'ret' definition under 'if (devfreq->suspend_freq) {'
>>>> because 'ret' is used if suspend_freq isn't zero.
>>> OK
>>
>> If you change the devfreq_resume_device() according to my new comment,
>> please ignore it.
>>
>>>>
>>>>> + unsigned long prev_freq;
>>>>
>>>> Remove prev_freq variable which is not used on this function.
>>>> After calling devfreq_set_target, prev_freq is not used.
>>> OK
>>>>
>>>>> + u32 flags = 0;
>>>>> +
>>>>> if (!devfreq)
>>>>> return -EINVAL;
>>>>>
>>>>> + if (devfreq->suspend_freq) {
In devfreq_resume_device(), it should check the 'devfreq->resume_freq'
instead of 'devfreq->suspend_freq'.
>>>>> + if (atomic_dec_return(&devfreq->suspend_count) >= 1)
>>>>> + return 0;
>>>>> +
>>>>> + ret = devfreq_set_target(devfreq, devfreq->resume_freq,
>>>>> + &prev_freq, flags);
>>>>
>>>> Remove the 'prev_freq' parameter.
>>> OK
>>>>
>>>>> + if (ret)
>>>>> + return ret;
>>>>> + }
>>>>> +
>>>>> if (!devfreq->governor)
>>>>> return 0;
>>
>> Please change the code as following because you uses the following type
>> in the devfreq_suspend_device(). If there is any special issue, please
>> keep the same format in order to improve the readability.
>>
>> if (devfreq->governor) {
>> ret = devfreq->governor->event_handler(devfreq,
>> DEVFREQ_GOV_RESUME, NULL);
>> if (ret)
>> return ret;
>> }
>>
>>
> OK, I will change the code to keep the same format.
> Thank you for the review.
>
> Regards,
> Lukasz
>
>
>
--
Best Regards,
Chanwoo Choi
Samsung Electronics
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