netdev - Re: How to fix WARN from drivers/base/dd.c in next-20200401 if CONFIG

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Date:   Fri, 3 Apr 2020 13:47:46 +0200
From:   Geert Uytterhoeven <geert@...ux-m68k.org>
To:     John Stultz <john.stultz@...aro.org>
Cc:     Yoshihiro Shimoda <yoshihiro.shimoda.uh@...esas.com>,
        "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
        "rafael@...nel.org" <rafael@...nel.org>,
        "iommu@...ts.linux-foundation.org" <iommu@...ts.linux-foundation.org>,
        LKML <linux-kernel@...r.kernel.org>,
        netdev <netdev@...r.kernel.org>
Subject: Re: How to fix WARN from drivers/base/dd.c in next-20200401 if CONFIG_MODULES=y?

Hi John,

On Thu, Apr 2, 2020 at 7:27 PM John Stultz <john.stultz@...aro.org> wrote:
> On Thu, Apr 2, 2020 at 3:17 AM Yoshihiro Shimoda
> <yoshihiro.shimoda.uh@...esas.com> wrote:
> >
> > I found an issue after applied the following patches:
> > ---
> > 64c775f driver core: Rename deferred_probe_timeout and make it global
> > 0e9f8d0 driver core: Remove driver_deferred_probe_check_state_continue()
> > bec6c0e pinctrl: Remove use of driver_deferred_probe_check_state_continue()
> > e2cec7d driver core: Set deferred_probe_timeout to a longer default if CONFIG_MODULES is set

Note that just setting deferred_probe_timeout = -1 like for the
CONFIG_MODULES=n case doesn't help.

> > c8c43ce driver core: Fix driver_deferred_probe_check_state() logic
> > ---
> >
> > Before these patches, on my environment [1], some device drivers
> > which has iommus property output the following message when probing:
> >
> > [    3.222205] ravb e6800000.ethernet: ignoring dependency for device, assuming no driver
> > [    3.257174] ravb e6800000.ethernet eth0: Base address at 0xe6800000, 2e:09:0a:02:eb:2d, IRQ 117.
> >
> > So, since ravb driver is probed within 4 seconds, we can use NFS rootfs correctly.
> >
> > However, after these patches are applied, since the patches are always waiting for 30 seconds
> > for of_iommu_configure() when IOMMU hardware is disabled, drivers/base/dd.c output WARN.
> > Also, since ravb cannot be probed for 30 seconds, we cannot use NFS rootfs anymore.
> > JFYI, I copied the kernel log to the end of this email.
>
> Hey,
>   Terribly sorry for the trouble. So as Robin mentioned I have a patch
> to remove the WARN messages, but I'm a bit more concerned about why
> after the 30 second delay, the ethernet driver loads:
>   [   36.218666] ravb e6800000.ethernet eth0: Base address at
> 0xe6800000, 2e:09:0a:02:eb:2d, IRQ 117.
> but NFS fails.
>
> Is it just that the 30 second delay is too long and NFS gives up?

I added some debug code to mount_nfs_root(), which shows that the first
3 tries happen before ravb is instantiated, and the last 3 tries happen
after.  So NFS root should work, if the network works.

However, it seems the Ethernet PHY is never initialized, hence the link
never becomes ready.  Dmesg before/after:

     ravb e6800000.ethernet eth0: Base address at 0xe6800000,
2e:09:0a:02:ea:ff, IRQ 108.

Good.

     ...
    -gpio_rcar e6052000.gpio: sense irq = 11, type = 8

This is the GPIO the PHY IRQ is connected to.
Note that that GPIO controller has been instantiated before.

     ...
    -Micrel KSZ9031 Gigabit PHY e6800000.ethernet-ffffffff:00:
attached PHY driver [Micrel KSZ9031 Gigabit PHY]
(mii_bus:phy_addr=e6800000.ethernet-ffffffff:00, irq=197)
     ...
    -ravb e6800000.ethernet eth0: Link is Up - 1Gbps/Full - flow control off

Oops.

    -Sending DHCP requests .., OK
    -IP-Config: Got DHCP answer from ...
     ...
    +VFS: Unable to mount root fs via NFS, trying floppy.
    +VFS: Cannot open root device "nfs" or unknown-block(2,0): error -6

> Does booting with deferred_probe_timeout=0 work?

It does, as now everything using optional links (DMA and IOMMU) is now
instantiated on first try.

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-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