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Date:   Mon, 18 Jan 2021 17:59:54 +0000
From:   Marc Zyngier <maz@kernel.org>
To:     Geert Uytterhoeven <geert@linux-m68k.org>
Cc:     Saravana Kannan <saravanak@google.com>,
        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>,
        Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>,
        Linux-Renesas <linux-renesas-soc@vger.kernel.org>
Subject: Re: [PATCH v1 5/5] driver core: Set fw_devlink=on by default
In-Reply-To: <CAMuHMdWDAg6+utMDLunPXmVtnP+13G2s0E-Fcnkc9bkNBs-cEg@mail.gmail.com>
References: <20201218031703.3053753-1-saravanak@google.com>
 <20201218031703.3053753-6-saravanak@google.com>
 <CAMuHMdWDAg6+utMDLunPXmVtnP+13G2s0E-Fcnkc9bkNBs-cEg@mail.gmail.com>
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Hi Geert,

On 2021-01-18 17:39, Geert Uytterhoeven wrote:
> 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").

There is a tentative patch from Saravana here[1], which works around
some issues on my RK3399 platform, and it'd be interesting to find
out whether that helps on your system.

Thanks,

         M.

[1] 
https://lore.kernel.org/r/20210116011412.3211292-1-saravanak@google.com
-- 
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