linux-kernel - Re: [PATCH] Revert "PM / devfreq: Modify the device name as devfreq(X) for sysfs"

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Date:   Fri, 21 Feb 2020 17:11:02 +0900
From:   Chanwoo Choi <cw00.choi@...sung.com>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        John Stultz <john.stultz@...aro.org>
Cc:     Orson Zhai <orson.unisoc@...il.com>,
        MyungJoo Ham <myungjoo.ham@...sung.com>,
        Kyungmin Park <kyungmin.park@...sung.com>,
        mingmin.ling@...soc.com, orsonzhai@...il.com,
        jingchao.ye@...soc.com, Linux PM list <linux-pm@...r.kernel.org>,
        lkml <linux-kernel@...r.kernel.org>,
        stable <stable@...r.kernel.org>
Subject: Re: [PATCH] Revert
 "PM / devfreq: Modify the device name as devfreq(X) for sysfs"

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@...uxfoundation.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@...aro.org>
>>>> Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
>>>> Cc: stable@...r.kernel.org
>>>> Signed-off-by: Orson Zhai <orson.unisoc@...il.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?
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?

-- 
Best Regards,
Chanwoo Choi
Samsung Electronics