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

From: Geert Uytterhoeven <geert@linux-m68k.org>
To: Ulf Hansson <ulf.hansson@linaro.org>
Cc: Saravana Kannan <saravanak@google.com>,
	Rob Herring <robh+dt@kernel.org>,
	Frank Rowand <frowand.list@gmail.com>,
	Android Kernel Team <kernel-team@android.com>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	DTML <devicetree@vger.kernel.org>
Subject: Re: [PATCH v2 1/2] of: platform: Make sure bus only devices get probed
Date: Tue, 7 Sep 2021 12:52:21 +0200	[thread overview]
Message-ID: <CAMuHMdVawd1_twGnWE7GzbPKXeKr+gCCXfodiBdECLScHRTBag@mail.gmail.com> (raw)
In-Reply-To: <CAPDyKFrGyOWSxe=0DGWNQ75YQgXVa62WF8=pOHNCWUh5PLcdqQ@mail.gmail.com>

Hi Ulf,

On Tue, Sep 7, 2021 at 12:36 PM Ulf Hansson <ulf.hansson@linaro.org> wrote:
> On Fri, 3 Sept 2021 at 16:29, Geert Uytterhoeven <geert@linux-m68k.org> wrote:
> > On Fri, Sep 3, 2021 at 11:19 AM Ulf Hansson <ulf.hansson@linaro.org> wrote:
> > > On Fri, 3 Sept 2021 at 01:04, Saravana Kannan <saravanak@google.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@google.com>
> > > > Tested-by: Saravana Kannan <saravanak@google.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").

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds