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From:   Geert Uytterhoeven <geert@linux-m68k.org>
Date:   Fri, 1 Jul 2022 09:38:55 +0200
Message-ID: <CAMuHMdW78nybK8LH2cDpM_0TCF-==QojaW8rKjudUhfJWNO0jA@mail.gmail.com>
Subject: Re: [PATCH v2 1/9] PM: domains: Delete usage of driver_deferred_probe_check_state()
To:     Saravana Kannan <saravanak@google.com>
Cc:     Tony Lindgren <tony@atomide.com>, Rob Herring <robh@kernel.org>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        "Rafael J. Wysocki" <rafael@kernel.org>,
        Kevin Hilman <khilman@kernel.org>,
        Ulf Hansson <ulf.hansson@linaro.org>,
        Len Brown <len.brown@intel.com>, Pavel Machek <pavel@ucw.cz>,
        Joerg Roedel <joro@8bytes.org>, Will Deacon <will@kernel.org>,
        Andrew Lunn <andrew@lunn.ch>,
        Heiner Kallweit <hkallweit1@gmail.com>,
        Russell King <linux@armlinux.org.uk>,
        "David S. Miller" <davem@davemloft.net>,
        Eric Dumazet <edumazet@google.com>,
        Jakub Kicinski <kuba@kernel.org>,
        Paolo Abeni <pabeni@redhat.com>,
        Linus Walleij <linus.walleij@linaro.org>,
        Hideaki YOSHIFUJI <yoshfuji@linux-ipv6.org>,
        David Ahern <dsahern@kernel.org>,
        Android Kernel Team <kernel-team@android.com>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Linux PM list <linux-pm@vger.kernel.org>,
        Linux IOMMU <iommu@lists.linux-foundation.org>,
        netdev <netdev@vger.kernel.org>,
        "open list:GPIO SUBSYSTEM" <linux-gpio@vger.kernel.org>,
        Alexander Stein <alexander.stein@ew.tq-group.com>
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Hi Saravana,

On Fri, Jul 1, 2022 at 1:11 AM Saravana Kannan <saravanak@google.com> wrote:
> On Mon, Jun 27, 2022 at 2:10 AM Tony Lindgren <tony@atomide.com> wrote:
> > * Saravana Kannan <saravanak@google.com> [220623 08:17]:
> > > On Thu, Jun 23, 2022 at 12:01 AM Tony Lindgren <tony@atomide.com> wrote:
> > > > * Saravana Kannan <saravanak@google.com> [220622 19:05]:
> > > > > On Tue, Jun 21, 2022 at 9:59 PM Tony Lindgren <tony@atomide.com> wrote:
> > > > > > This issue is no directly related fw_devlink. It is a side effect of
> > > > > > removing driver_deferred_probe_check_state(). We no longer return
> > > > > > -EPROBE_DEFER at the end of driver_deferred_probe_check_state().
> > > > >
> > > > > Yes, I understand the issue. But driver_deferred_probe_check_state()
> > > > > was deleted because fw_devlink=on should have short circuited the
> > > > > probe attempt with an  -EPROBE_DEFER before reaching the bus/driver
> > > > > probe function and hitting this -ENOENT failure. That's why I was
> > > > > asking the other questions.
> > > >
> > > > OK. So where is the -EPROBE_DEFER supposed to happen without
> > > > driver_deferred_probe_check_state() then?
> > >
> > > device_links_check_suppliers() call inside really_probe() would short
> > > circuit and return an -EPROBE_DEFER if the device links are created as
> > > expected.
> >
> > OK
> >
> > > > Hmm so I'm not seeing any supplier for the top level ocp device in
> > > > the booting case without your patches. I see the suppliers for the
> > > > ocp child device instances only.
> > >
> > > Hmmm... this is strange (that the device link isn't there), but this
> > > is what I suspected.
> >
> > Yup, maybe it's because of the supplier being a device in the child
> > interconnect for the ocp.
>
> Ugh... yeah, this is why the normal (not SYNC_STATE_ONLY) device link
> isn't being created.
>
> So the aggregated view is something like (I had to set tabs = 4 space
> to fit it within 80 cols):
>
>     ocp: ocp {         <========================= Consumer
>         compatible = "simple-pm-bus";
>         power-domains = <&prm_per>; <=========== Supplier ref
>
>                 l4_wkup: interconnect@44c00000 {
>             compatible = "ti,am33xx-l4-wkup", "simple-pm-bus";
>
>             segment@200000 {  /* 0x44e00000 */
>                 compatible = "simple-pm-bus";
>
>                 target-module@0 { /* 0x44e00000, ap 8 58.0 */
>                     compatible = "ti,sysc-omap4", "ti,sysc";
>
>                     prcm: prcm@0 {
>                         compatible = "ti,am3-prcm", "simple-bus";
>
>                         prm_per: prm@c00 { <========= Actual Supplier
>                             compatible = "ti,am3-prm-inst", "ti,omap-prm-inst";
>                         };
>                     };
>                 };
>             };
>         };
>     };
>
> The power-domain supplier is the great-great-great-grand-child of the
> consumer. It's not clear to me how this is valid. What does it even
> mean?
>
> Rob, is this considered a valid DT?
>
> Geert, thoughts on whether this is a correct use of simple-pm-bus device?

Well, if the hardware is wired that way...

It's not that dissimilar from CPU cores, and interrupt and GPIO
controllers in power domains and clocked by controllable clocks:
you can cut the branch you're sitting on, and you have to be careful
when going to sleep, and make sure your wake-up sources are still
functional.

> Also, how is the power domain attach/get working in this case? As far
> as I can tell, at least for "simple-pm-bus" devices, the pm domain
> attachment is happening under:
> really_probe() -> call_driver_probe -> platform_probe() ->
> dev_pm_domain_attach()
>
> So, how is the pm domain attach succeeding in the first place without
> my changes?

That's a software thing ;-)

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