linux-kernel - Re: [PATCH v2 1/2] of: platform: Make sure bus only devices get probed

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Date:   Tue, 7 Sep 2021 13:02:15 +0200
From:   Ulf Hansson <ulf.hansson@...aro.org>
To:     Geert Uytterhoeven <geert@...ux-m68k.org>
Cc:     Saravana Kannan <saravanak@...gle.com>,
        Rob Herring <robh+dt@...nel.org>,
        Frank Rowand <frowand.list@...il.com>,
        Android Kernel Team <kernel-team@...roid.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        DTML <devicetree@...r.kernel.org>
Subject: Re: [PATCH v2 1/2] of: platform: Make sure bus only devices get probed

On Tue, 7 Sept 2021 at 12:52, Geert Uytterhoeven <geert@...ux-m68k.org> wrote:
>
> Hi Ulf,
>
> On Tue, Sep 7, 2021 at 12:36 PM Ulf Hansson <ulf.hansson@...aro.org> wrote:
> > On Fri, 3 Sept 2021 at 16:29, Geert Uytterhoeven <geert@...ux-m68k.org> wrote:
> > > On Fri, Sep 3, 2021 at 11:19 AM Ulf Hansson <ulf.hansson@...aro.org> wrote:
> > > > On Fri, 3 Sept 2021 at 01:04, Saravana Kannan <saravanak@...gle.com> wrote:
> > > > > fw_devlink could end up creating device links for bus only devices.
> > > > > However, bus only devices don't get probed and can block probe() or
> > > > > sync_state() [1] call backs of other devices. To avoid this, set up
> > > > > these devices to get probed by the simple-pm-bus.
> > > > >
> > > > > [1] - https://lore.kernel.org/lkml/CAPDyKFo9Bxremkb1dDrr4OcXSpE0keVze94Cm=zrkOVxHHxBmQ@mail.gmail.com/
> > > > > Signed-off-by: Saravana Kannan <saravanak@...gle.com>
> > > > > Tested-by: Saravana Kannan <saravanak@...gle.com>
> > > >
> > > > Again, this looks like a nice solution to the problem.
> > > >
> > > > One question though. The Kconfig SIMPLE_PM_BUS, should probably be
> > > > "default y" - or something along those lines to make sure fw_devlink
> > > > works as expected.
> > >
> > > I would love for SIMPLE_PM_BUS to go away, and all of its functionality
> > > to be usurped by the standard simple-bus handling.
> > >
> > > In the modern world, everything uses power management and Runtime
> > > PM, and the distinction between "simple-bus" and "simple-pm-bus"
> > > is purely artificial.
> >
> > I think it's not that easy, but maybe I am wrong.
> >
> > Today we have an opt-in way of supporting runtime PM (and power
> > management). In most cases it's up to drivers or subsystem level code
> > to decide if runtime PM should be enabled for the device.
> >
> > Would it really be okay to enable runtime PM for all of them?
>
> You're talking about the software policy side.
>
> From my PoV, the issue is that this decision is leaked into DT, through
> the different compatible values ("simple-pm-bus" vs. "simple-bus").

Yes, I do agree with you there.

On the other hand, it's probably not the only place where it's used as
"software configuration", so I don't have a big issue with it.

Kind regards
Uffe