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From:   Saravana Kannan <saravanak@google.com>
Date:   Thu, 28 Jan 2021 09:04:57 -0800
Message-ID: <CAGETcx-GbSEYxWTB+sDQCh9-sQmKi=ejcBf=036YeQhY-DQu9A@mail.gmail.com>
Subject: Re: [PATCH v1 5/5] driver core: Set fw_devlink=on by default
To:     Tudor.Ambarus@microchip.com
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        "Rafael J. Wysocki" <rafael@kernel.org>,
        Android Kernel Team <kernel-team@android.com>,
        LKML <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>,
        Geert Uytterhoeven <geert@linux-m68k.org>,
        Nicolas.Ferre@microchip.com, Ludovic.Desroches@microchip.com,
        alexandre.belloni@bootlin.com, Claudiu.Beznea@microchip.com
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On Thu, Jan 28, 2021 at 2:59 AM <Tudor.Ambarus@microchip.com> wrote:
>
> Hi, Saravana,
>
> On 1/25/21 8:16 PM, Saravana Kannan wrote:
> > EXTERNAL EMAIL: Do not click links or open attachments unless you know the content is safe
> >
> > On Mon, Jan 25, 2021 at 9:05 AM <Tudor.Ambarus@microchip.com> wrote:
> >>
> >> Hi, Saravana,
> >>
> >> On 12/18/20 5:17 AM, Saravana Kannan 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>
> >>
> >> next-20210125 fails to boot on at91 sama5d2 platforms. No output is
> >> seen, unless earlyprintk is enabled.
> >>
> >> I have bisected this to commit e590474768f1cc04 ("driver core: Set
> >> fw_devlink=on by default").
> >>
> >> I've attached a log that I'm seeing on a sama5d2_xplained (sama5_defconfig
> >> and arch/arm/boot/dts/at91-sama5d2_xplained.dts). I enabled the
> >> following logs:
> >> 1. The ones in device_links_check_suppliers()
> >> 2. The ones in device_link_add()
> >> 3. initcall_debug=1
> >>
> >> There seem to be some probe fails due to the pmc supplier not being ready:
> >> calling  at_xdmac_init+0x0/0x18 @ 1
> >> platform f0010000.dma-controller: probe deferral - supplier f0014000.pmc not ready
> >> platform f0004000.dma-controller: probe deferral - supplier f0014000.pmc not ready
> >> initcall at_xdmac_init+0x0/0x18 returned -19 after 19531 usecs
> >>
> >> calling  udc_driver_init+0x0/0x18 @ 1
> >> platform 300000.gadget: probe deferral - supplier f0014000.pmc not ready
> >> initcall udc_driver_init+0x0/0x18 returned -19 after 7524 usecs
> >>
> >> There are others too. I'm checking them.
> >
> > Thanks Tudor. I'll look into this within a few days. I'm also looking
> > into coming up with a more generic solution.
> >
>
> I've sent a patch addressing this at:
> https://lore.kernel.org/lkml/20210128104446.164269-1-tudor.ambarus@microchip.com/T/#u
>
> Can you please take a look?

Thanks for taking a look at this. I responded in that thread.

-Saravana