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From:   Geert Uytterhoeven <geert@linux-m68k.org>
Date:   Mon, 18 Jan 2021 18:39:10 +0100
Message-ID: <CAMuHMdWDAg6+utMDLunPXmVtnP+13G2s0E-Fcnkc9bkNBs-cEg@mail.gmail.com>
Subject: Re: [PATCH v1 5/5] driver core: Set fw_devlink=on by default
To:     Saravana Kannan <saravanak@google.com>
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        "Rafael J. Wysocki" <rafael@kernel.org>,
        Android Kernel Team <kernel-team@android.com>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Jisheng Zhang <Jisheng.Zhang@synaptics.com>,
        Kevin Hilman <khilman@baylibre.com>,
        John Stultz <john.stultz@linaro.org>,
        Nicolas Saenz Julienne <nsaenzjulienne@suse.de>,
        Marc Zyngier <maz@kernel.org>,
        Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>,
        Linux-Renesas <linux-renesas-soc@vger.kernel.org>
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Hi Saravana,

On Fri, Dec 18, 2020 at 4:34 AM Saravana Kannan <saravanak@google.com> wrote:
> Cyclic dependencies in some firmware was one of the last remaining
> reasons fw_devlink=on couldn't be set by default. Now that cyclic
> dependencies don't block probing, set fw_devlink=on by default.
>
> Setting fw_devlink=on by default brings a bunch of benefits (currently,
> only for systems with device tree firmware):
> * Significantly cuts down deferred probes.
> * Device probe is effectively attempted in graph order.
> * Makes it much easier to load drivers as modules without having to
>   worry about functional dependencies between modules (depmod is still
>   needed for symbol dependencies).
>
> If this patch prevents some devices from probing, it's very likely due
> to the system having one or more device drivers that "probe"/set up a
> device (DT node with compatible property) without creating a struct
> device for it.  If we hit such cases, the device drivers need to be
> fixed so that they populate struct devices and probe them like normal
> device drivers so that the driver core is aware of the devices and their
> status. See [1] for an example of such a case.
>
> [1] - https://lore.kernel.org/lkml/CAGETcx9PiX==mLxB9PO8Myyk6u2vhPVwTMsA5NkD-ywH5xhusw@mail.gmail.com/
> Signed-off-by: Saravana Kannan <saravanak@google.com>

Shimoda-san reported that next-20210111 and later fail to boot
on Renesas R-Car Gen3 platforms. No output is seen, unless earlycon
is enabled.

I have bisected this to commit e590474768f1cc04 ("driver core: Set
fw_devlink=on by default").

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