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Subject: Re: [PATCH] Revert
 "PM / devfreq: Modify the device name as devfreq(X) for sysfs"
To:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Chanwoo Choi <chanwoo@kernel.org>
Cc:     John Stultz <john.stultz@linaro.org>,
        Orson Zhai <orson.unisoc@gmail.com>,
        MyungJoo Ham <myungjoo.ham@samsung.com>,
        Kyungmin Park <kyungmin.park@samsung.com>,
        mingmin.ling@unisoc.com, orsonzhai@gmail.com,
        jingchao.ye@unisoc.com, Linux PM list <linux-pm@vger.kernel.org>,
        lkml <linux-kernel@vger.kernel.org>,
        stable <stable@vger.kernel.org>
From:   Chanwoo Choi <cw00.choi@samsung.com>
Organization: Samsung Electronics
Message-ID: <76f1ac9b-f130-d6f6-eb04-e81f9f06451e@samsung.com>
Date:   Mon, 24 Feb 2020 11:17:04 +0900
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On 2/24/20 2:54 AM, Greg Kroah-Hartman wrote:
> On Sat, Feb 22, 2020 at 08:55:22AM +0900, Chanwoo Choi wrote:
>> On Fri, Feb 21, 2020 at 8:13 PM Greg Kroah-Hartman
>> <gregkh@linuxfoundation.org> wrote:
>>>
>>> On Fri, Feb 21, 2020 at 05:11:02PM +0900, Chanwoo Choi wrote:
>>>> On 2/21/20 4:06 PM, Greg Kroah-Hartman wrote:
>>>>> On Thu, Feb 20, 2020 at 11:47:41AM -0800, John Stultz wrote:
>>>>>> On Thu, Feb 20, 2020 at 11:15 AM Greg Kroah-Hartman
>>>>>> <gregkh@linuxfoundation.org> wrote:
>>>>>>>
>>>>>>> On Fri, Feb 21, 2020 at 01:37:04AM +0800, Orson Zhai wrote:
>>>>>>>> This reverts commit 4585fbcb5331fc910b7e553ad3efd0dd7b320d14.
>>>>>>>>
>>>>>>>> The name changing as devfreq(X) breaks some user space applications,
>>>>>>>> such as Android HAL from Unisoc and Hikey [1].
>>>>>>>> The device name will be changed unexpectly after every boot depending
>>>>>>>> on module init sequence. It will make trouble to setup some system
>>>>>>>> configuration like selinux for Android.
>>>>>>>>
>>>>>>>> So we'd like to revert it back to old naming rule before any better
>>>>>>>> way being found.
>>>>>>>>
>>>>>>>> [1] https://protect2.fireeye.com/url?k=00fa721e-5d2a7af6-00fbf951-000babff32e3-95e4b92259b05656&u=https://lkml.org/lkml/2018/5/8/1042
>>>>>>>>
>>>>>>>> Cc: John Stultz <john.stultz@linaro.org>
>>>>>>>> Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
>>>>>>>> Cc: stable@vger.kernel.org
>>>>>>>> Signed-off-by: Orson Zhai <orson.unisoc@gmail.com>
>>>>>>>>
>>>>>>>> ---
>>>>>>>>  drivers/devfreq/devfreq.c | 4 +---
>>>>>>>>  1 file changed, 1 insertion(+), 3 deletions(-)
>>>>>>>>
>>>>>>>> diff --git a/drivers/devfreq/devfreq.c b/drivers/devfreq/devfreq.c
>>>>>>>> index cceee8b..7dcf209 100644
>>>>>>>> --- a/drivers/devfreq/devfreq.c
>>>>>>>> +++ b/drivers/devfreq/devfreq.c
>>>>>>>> @@ -738,7 +738,6 @@ struct devfreq *devfreq_add_device(struct device *dev,
>>>>>>>>  {
>>>>>>>>       struct devfreq *devfreq;
>>>>>>>>       struct devfreq_governor *governor;
>>>>>>>> -     static atomic_t devfreq_no = ATOMIC_INIT(-1);
>>>>>>>>       int err = 0;
>>>>>>>>
>>>>>>>>       if (!dev || !profile || !governor_name) {
>>>>>>>> @@ -800,8 +799,7 @@ struct devfreq *devfreq_add_device(struct device *dev,
>>>>>>>>       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));
>>>>>>>> +     dev_set_name(&devfreq->dev, "%s", dev_name(dev));
>>>>>>>>       err = device_register(&devfreq->dev);
>>>>>>>>       if (err) {
>>>>>>>>               mutex_unlock(&devfreq->lock);
>>>>>>>> --
>>>>>>>> 2.7.4
>>>>>>>>
>>>>>>>
>>>>>>> Thanks for this, I agree, this needs to get back to the way things were
>>>>>>> as it seems to break too many existing systems as-is.
>>>>>>>
>>>>>>> I'll queue this up in my tree now, thanks.
>>>>>>
>>>>>> Oof this old thing. I unfortunately didn't get back to look at the
>>>>>> devfreq name node issue or the compatibility links, since the impact
>>>>>> of the regression (breaking the powerHAL's interactions with the gpu)
>>>>>> wasn't as big as other problems we had. While the regression was
>>>>>> frustrating, my only hesitancy at this point is that its been this way
>>>>>> since 4.10, so reverting the problematic patch is likely to break any
>>>>>> new users since then.
>>>>>
>>>>> Looks like most users just revert that commit in their trees:
>>>>>     https://protect2.fireeye.com/url?k=1012ad0f-4dc2a5e7-10132640-000babff32e3-35779c5ed675ef0f&u=https://source.codeaurora.org/quic/la/kernel/msm-4.14/commit/drivers/devfreq?h=msm-4.14&id=ccf273f6d89ad0fa8032e9225305ad6f62c7770c
>>>>>
>>>>> So we should be ok here.
>>>>
>>>> I'm sorry about changing the devfreq node name.
>>>>
>>>> OK. Do you pick this patch to your tree?
>>>
>>> Yes, I can do that.
>>
>> If you agree, how about merging it to devfreq.git
>> for preventing the potential merge conflict with other devfreq patches?
> 
> Sure, but it should go for 5.6-final, right?

OK.I'll send pull-request of this patch for v5.6-rc4.

> 
>>>> or If not, I'll apply it to devfreq-next branch for v5.7-rc1.
>>>>
>>>> And do you apply it to kernel of linux-stable tree since 4.11?
>>>
>>> Yeah, I'll mark it for stable.
>>
>> Thanks.
>>
>>>
>>> Can I get an ack from you for this?
>>
>> OK. but, if it will be merged to devfreq.git,
>> can I get an ack from you?
> 
> Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Thanks. I applied it to devfreq-fixes branch for v5.6-rc4.

-- 
Best Regards,
Chanwoo Choi
Samsung Electronics