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From:   Geert Uytterhoeven <geert@linux-m68k.org>
Date:   Mon, 15 Feb 2021 16:16:27 +0100
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Subject: Re: [PATCH v4 0/8] Make fw_devlink=on more forgiving
To:     Saravana Kannan <saravanak@google.com>
Cc:     Jonathan Corbet <corbet@lwn.net>,
        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>, Len Brown <lenb@kernel.org>,
        Pavel Machek <pavel@ucw.cz>,
        Michael Turquette <mturquette@baylibre.com>,
        Stephen Boyd <sboyd@kernel.org>,
        Rob Herring <robh+dt@kernel.org>,
        Frank Rowand <frowand.list@gmail.com>,
        Marc Zyngier <maz@kernel.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        "open list:DOCUMENTATION" <linux-doc@vger.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
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        linux-clk <linux-clk@vger.kernel.org>,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <devicetree@vger.kernel.org>,
        ACPI Devel Maling List <linux-acpi@vger.kernel.org>,
        Marek Szyprowski <m.szyprowski@samsung.com>,
        Android Kernel Team <kernel-team@android.com>,
        Linux-Renesas <linux-renesas-soc@vger.kernel.org>
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Hi Saravana,

On Fri, Feb 12, 2021 at 4:00 AM Saravana Kannan <saravanak@google.com> wrote:
> On Thu, Feb 11, 2021 at 5:00 AM Geert Uytterhoeven <geert@linux-m68k.org> wrote:
> >   1. R-Car Gen2 (Koelsch), R-Car Gen3 (Salvator-X(S), Ebisu).
> >
> >       - Commit 2dfc564bda4a31bc ("soc: renesas: rcar-sysc: Mark device
> >         node OF_POPULATED after init") is no longer needed (but already
> >         queued for v5.12 anyway)
>
> Rob doesn't like the proliferation of OF_POPULATED and we don't need
> it anymore, so maybe work it out with him? It's a balance between some
> wasted memory (struct device(s)) vs not proliferating OF_POPULATED.

> >   2. SH/R-Mobile AG5 (kzm9g), APE6 (ape6evm), A1 (armadillo800-eva)
> >
> >       - "PATCH] soc: renesas: rmobile-sysc: Set OF_POPULATED and absorb
> >         reset handling" is no longer needed
> >         https://lore.kernel.org/linux-arm-kernel/20210205133319.1921108-1-geert+renesas@glider.be/
>
> Good to see more evidence that this series is fixing things at a more
> generic level.

I spoke too soon: if CONFIG_POWER_RESET_RMOBILE=n,
booting fails again, as everything is waiting on the system controller,
which never becomes available.
Rcar-sysc doesn't suffer from this problem, cfr. above.
Perhaps because the rmobile-sysc bindings use a hierarchical instead
of a linear PM domain description, and thus consumers point to the
children of the system controller node?
Cfr. system-controller@e6180000 in arch/arm/boot/dts/r8a7740.dtsi.

> >       - On R-Mobile A1, I get a BUG and a memory leak:
> >
> >             BUG: spinlock bad magic on CPU#0, swapper/1
> >              lock: lcdc0_device+0x10c/0x308, .magic: 00000000, .owner:
> > <none>/-1, .owner_cpu: 0
> >             CPU: 0 PID: 1 Comm: swapper Not tainted
> > 5.11.0-rc5-armadillo-00032-gf0a85c26907e #266
> >             Hardware name: Generic R8A7740 (Flattened Device Tree)
> >             [<c010c3c8>] (unwind_backtrace) from [<c010a49c>]
> > (show_stack+0x10/0x14)
> >             [<c010a49c>] (show_stack) from [<c0159534>]
> > (do_raw_spin_lock+0x20/0x94)
> >             [<c0159534>] (do_raw_spin_lock) from [<c04089d8>]
> > (dev_pm_get_subsys_data+0x30/0xa0)
> >             [<c04089d8>] (dev_pm_get_subsys_data) from [<c0413698>]
> > (genpd_add_device+0x34/0x1c0)
> >             [<c0413698>] (genpd_add_device) from [<c041389c>]
> > (of_genpd_add_device+0x34/0x4c)
> >             [<c041389c>] (of_genpd_add_device) from [<c0a1e9bc>]
> > (board_staging_register_device+0xf8/0x118)
> >             [<c0a1e9bc>] (board_staging_register_device) from

This is indeed a pre-existing problem.
of_genpd_add_device() is called before platform_device_register(),
as it needs to attach the genpd before the device is probed.
But the spinlock is only initialized when the device is registered.
This was masked before due to an unrelated wait context check failure,
which disabled any further spinlock checks, and exposed by fw_devlinks
changing probe order.
Patch sent.
"[PATCH] staging: board: Fix uninitialized spinlock when attaching genpd"
https://lore.kernel.org/r/20210215151405.2551143-1-geert+renesas@glider.be


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