linux-kernel - Re: [PATCH v1 5/5] driver core: Set fw

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Date:   Mon, 25 Jan 2021 10:16:55 -0800
From:   Saravana Kannan <saravanak@...gle.com>
To:     Tudor.Ambarus@...rochip.com
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Android Kernel Team <kernel-team@...roid.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Jisheng Zhang <Jisheng.Zhang@...aptics.com>,
        Kevin Hilman <khilman@...libre.com>,
        John Stultz <john.stultz@...aro.org>,
        Nicolas Saenz Julienne <nsaenzjulienne@...e.de>,
        Marc Zyngier <maz@...nel.org>,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        Nicolas.Ferre@...rochip.com, Ludovic.Desroches@...rochip.com,
        alexandre.belloni@...tlin.com, Claudiu.Beznea@...rochip.com
Subject: Re: [PATCH v1 5/5] driver core: Set fw_devlink=on by default

On Mon, Jan 25, 2021 at 9:05 AM <Tudor.Ambarus@...rochip.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@...gle.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.

-Saravana