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Message-ID: <7662d626-5c3e-aec5-05e4-c6cd2e56ef49@partner.samsung.com>
Date: Tue, 4 Dec 2018 10:53:25 +0100
From: Lukasz Luba <l.luba@...tner.samsung.com>
To: Chanwoo Choi <cw00.choi@...sung.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 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;
---->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;
---->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;
>>>>
>>>
>>>
>>
>>
>
>
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