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

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Date:   Sun, 28 Mar 2021 19:26:58 +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 06:07:10PM +0200, Daniel Lezcano wrote:
> 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 would recommend fixing that up if you can rebase it.  If not, you need
to revert it and start over.  I'll be glad to review it if you cc: me on
the patches.

> 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 ?

This has nothing to do with the Android kernel workflow, sorry.  I am
concerned about proper kernel development and keeping bugs out of it.

thanks,

greg k-h