linux-kernel - Re: [PATCH v4 2/5] powercap/drivers/dtpm: Create a registering system

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Date:   Sun, 28 Mar 2021 18:07:10 +0200
From:   Daniel Lezcano <daniel.lezcano@...aro.org>
To:     Greg KH <gregkh@...uxfoundation.org>
Cc:     rafael@...nel.org, linux-kernel@...r.kernel.org,
        linux-pm@...r.kernel.org, lukasz.luba@....com
Subject: Re: [PATCH v4 2/5] powercap/drivers/dtpm: Create a registering system

On 28/03/2021 13:24, Greg KH wrote:
> On Sun, Mar 28, 2021 at 01:11:30PM +0200, Daniel Lezcano wrote:
>>
>> Hi Greg,
>>
>> On 28/03/2021 08:50, Greg KH wrote:
>>
>> [ ... ]
>>
>>>>> And any reason why you are not using "real" struct devices in this
>>>>> subsystem?  You seem to be rolling your own infrastructure for no good
>>>>> reason.  I imagine you want sysfs support next, right?
>>>>
>>>> Actually, the framework is on top of powercap, so it has de facto the
>>>> sysfs support. On the other side, the dtpm backends are tied with the
>>>> device they manage.
>>>
>>> So why are they not a "real" device in the driver model?  It looks like
>>> you almost are wanting all of that functionality and are having to
>>> implement it "by hand" instead.
>>
>> I'm sorry I misunderstanding your point. dtpm is the backend for the
>> powercap subsystem which is the generic subsystem to do power limitation.
>>
>> We have:
>>
>> struct dtpm_cpu {
>> 	struct dtpm dtmp;
>> 	...
>> }
>>
>> struct dtpm {
>> 	struct powercap powecap;
>> };
>>
>> struct powercap {
>> 	struct device dev;
>> };
> 
> Oh nice.  So you can not use a kref here at all as you already have a
> reference counted device controling your structure.  You can not have 2
> references trying to control the same structure, that way lies madness
> and bugs :(
> 
> So why are you trying to add a kref here as the structure already has
> support for proper lifetimes?

Right, I'll revisit that part. Thanks for the review.

I've a branch which is pulled by Rafael [1]. These parts are already
merged in the dtpm/next branch but not yet in Rafael's tree.

I think a rebase is possible but I would like to avoid that. Would be a
patch on top of the dtpm/next acceptable given your flow with Android ?

  -- Daniel

[1]
https://git.kernel.org/pub/scm/linux/kernel/git/daniel.lezcano/linux.git/log/?h=dtpm/next

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