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

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Date:   Sun, 28 Mar 2021 13:24:51 +0200
From:   Greg KH <gregkh@...uxfoundation.org>
To:     Daniel Lezcano <daniel.lezcano@...aro.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 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?

thanks,

greg k-h