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Message-id: <54BE02F3.4060808@samsung.com>
Date: Tue, 20 Jan 2015 16:25:39 +0900
From: Chanwoo Choi <cw00.choi@...sung.com>
To: myungjoo.ham@...sung.com
Cc: "kgene@...nel.org" <kgene@...nel.org>,
박경민 <kyungmin.park@...sung.com>,
"rafael.j.wysocki@...el.com" <rafael.j.wysocki@...el.com>,
"mark.rutland@....com" <mark.rutland@....com>,
ABHILASH KESAVAN <a.kesavan@...sung.com>,
"tomasz.figa@...il.com" <tomasz.figa@...il.com>,
Krzysztof Kozlowski <k.kozlowski@...sung.com>,
Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>,
"robh+dt@...nel.org" <robh+dt@...nel.org>,
대인기 <inki.dae@...sung.com>,
"linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
"linux-arm-kernel@...ts.infradead.org"
<linux-arm-kernel@...ts.infradead.org>,
"linux-samsung-soc@...r.kernel.org"
<linux-samsung-soc@...r.kernel.org>
Subject: Re: [PATCHv8 1/9] devfreq: event: Add new devfreq_event class to
provide basic data for devfreq governor
Dear Myungjoo,
On 01/20/2015 03:59 PM, MyungJoo Ham wrote:
>>
>> Dear Myungjoo,
>>
>> On 01/20/2015 01:34 PM, MyungJoo Ham wrote:
>>>>
> []
>>>> +
>>>> + mutex_lock(&edev->lock);
>>>> + if (edev->desc->ops && edev->desc->ops->enable) {
>>>> + ret = edev->desc->ops->enable(edev);
>>>> + if (ret < 0)
>>>> + goto err;
>>>> + }
>>>
>>> Is there any reason to call enable(edev) even when enable_count is already > 0
>>> while you do not call disable(edev) while enable_count > 0?
>>>
>>> I think this may incur errors in the related device drivers.
>>> (e.g., incorrect pairing of clk/runtime-pm/regulator enable/disable
>>> at the device driver side)
>>
>> You're right. This part has potential errors. I'll fix it as following:
>> If edev is already enabled, devfreq_event_enable_edev() will just return
>> without any operation because devfreq-event(edev) can handle only one event
>> at the same time.
>>
>> mutex_lock(&edev->lock);
>> if (edev->enable_count)
>> dev_warn(&edev->dev, "%s is already enabled\n", edev->desc->name);
>> ret = -EINVAL;
>> goto err;
>> }
>>
>> if (edev->desc->ops && edev->desc->ops->enable) {
>> ret = edev->desc->ops->enable(edev);
>> if (ret < 0)
>> goto err;
>> }
>> edev->enable_count++;
>
> No, your suggested modification creates another bug.
>
> It should not emit "warn" when enable_count > 0 at enable().
> It is a natural behavior from drivers.
> - You may have multiple drivers using edev.
> - You may have multiple threads using edev.
The devfreq-event cannot be used in multiple drivers in current version
If multiple driver set the event to devfreq-event device by using
devfreq_event_set_event() at the same time, previous event will be ignored.
If multiple drivers want to use devfreq-event device at the same time,
I have to implement additional feature.
>
> Thus, the above 12 lines should be replaced with:
>
> if (edev->desc->ops && edev->desc->ops->enable &&
> edev->enable_count == 0) {
> ret = edev->desc->ops->enable(edev);
> if (ret < 0)
> goto err;
> }
> edev->enable_count++;
>
>>
>>
>>>
>>>> + edev->enable_count++;
>>>> +err:
>>>> + mutex_unlock(&edev->lock);
>>>> +
>>>> + return ret;
>>>> +}
>>>> +EXPORT_SYMBOL_GPL(devfreq_event_enable_edev);
>>>> +
>>>> +/**
>>>> + * devfreq_event_disable_edev() - Disable the devfreq-event dev and decrease
>>>> + * the enable_count of the devfreq-event dev.
>>>> + * @edev : the devfreq-event device
>>>> + *
>>>> + * Note that this function decrease the enable_count and disable the
>>>> + * devfreq-event device. After the devfreq-event device is disabled,
>>>> + * devfreq device can't use the devfreq-event device for get/set/reset
>>>> + * operations.
>>>> + */
>>>> +int devfreq_event_disable_edev(struct devfreq_event_dev *edev)
>>>> +{
>>>> + int ret = 0;
>>>> +
>>>> + if (!edev || !edev->desc)
>>>> + return -EINVAL;
>>>> +
>>>> + mutex_lock(&edev->lock);
>>>> + if (edev->enable_count > 0) {
>>>> + edev->enable_count--;
>>>> + } else {
>>>> + dev_warn(&edev->dev, "unbalanced enable_count\n");
>>>> + ret = -EINVAL;
>>>> + goto err;
>>>> + }
>>>> +
>>>> + if (edev->desc->ops && edev->desc->ops->disable) {
>>>> + ret = edev->desc->ops->disable(edev);
>>>> + if (ret < 0) {
>>>> + edev->enable_count++;
>>>> + goto err;
>>>> + }
>
> Anyway, have you seen other subsystems doing fall-back operations as you've
> done by "edev->enable_count++" here? Or is this your own idea on falling back
> from errors with a disable callback?
I removed "edev->enable_count++" when fail to diable devfreq-event
and modify it as following:
+int devfreq_event_disable_edev(struct devfreq_event_dev *edev)
+{
+ int ret = 0;
+
+ if (!edev || !edev->desc)
+ return -EINVAL;
+
+ mutex_lock(&edev->lock);
+ if (!edev->enable_count) {
+ dev_warn(&edev->dev,
+ "%s is already disabled\n", edev->desc->name);
+ goto err;
+ }
+
+ if (edev->desc->ops && edev->desc->ops->disable) {
+ ret = edev->desc->ops->disable(edev);
+ if (ret < 0)
+ goto err;
+ }
+ edev->enable_count--;
+err:
+ mutex_unlock(&edev->lock);
+
+ return ret;
+}
+EXPORT_SYMBOL_GPL(devfreq_event_disable_edev);
>
>>>> + }
>>>
>>> You did it correctly with disable here;
>>> not calling it when it is not required.
>
> Uh..yeah.. the original patch was incorrect..
>
>>
>> As I explained, I'll fix it as following:
>>
>> mutex_lock(&edev->lock);
>> if (!edev->enable_count) {
>> dev_warn(&edev->dev, "%s is already disabled\n", edev->desc->name);
>> ret = -EINVAL;
>> goto err;
>> }
>>
>> if (edev->desc->ops && edev->desc->ops->disable) {
>> ret = edev->desc->ops->disable(edev);
>> if (ret < 0)
>> goto err;
>> }
>> edev->enable_count--;
>
> Uh.... I'd say it is still incorrect.
I explained it about this problem on the upper.
>
> mutex_lock(&edev->lock);
> if (!edev->enable_count) {
> dev_warn(&edev->dev, "%s is already disabled\n", edev->desc->name);
> ret = -EINVAL;
> goto err;
> }
>
> edev->enable_count--;
> if (edev->desc->ops && edev->desc->ops->disable &&
> !edev->enable_count) {
> ret = edev->desc->ops->disable(edev);
> if (ret < 0)
> goto err;
> }
[snip]
Best Regards,
Chanwoo Choi
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