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From:   Olof Johansson <olof@lixom.net>
Date:   Mon, 19 Sep 2022 15:56:09 -0700
Message-ID: <CAOesGMh5GHCONTQ9M1Ro7zW-hkL_1F7Xt=xRV0vYSfPY=7LYkQ@mail.gmail.com>
Subject: Re: [PATCH v2 0/2] Fix console probe delay when stdout-path isn't set
To:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc:     Saravana Kannan <saravanak@google.com>,
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Precedence: bulk

On Mon, Sep 19, 2022 at 1:44 AM Greg Kroah-Hartman
<gregkh@linuxfoundation.org> wrote:
>
> On Sun, Sep 18, 2022 at 08:44:27PM -0700, Olof Johansson wrote:
> > On Tue, Aug 23, 2022 at 8:37 AM Greg Kroah-Hartman
> > <gregkh@linuxfoundation.org> wrote:
> > >
> > > On Thu, Jun 30, 2022 at 06:26:38PM -0700, Saravana Kannan wrote:
> > > > These patches are on top of driver-core-next.
> > > >
> > > > Even if stdout-path isn't set in DT, this patch should take console
> > > > probe times back to how they were before the deferred_probe_timeout
> > > > clean up series[1].
> > >
> > > Now dropped from my queue due to lack of a response to other reviewer's
> > > questions.
> >
> > What happened to this patch? I have a 10 second timeout on console
> > probe on my SiFive Unmatched, and I don't see this flag being set for
> > the serial driver. In fact, I don't see it anywhere in-tree. I can't
> > seem to locate another patchset from Saravana around this though, so
> > I'm not sure where to look for a missing piece for the sifive serial
> > driver.
> >
> > This is the second boot time regression (this one not fatal, unlike
> > the Layerscape PCIe one) from the fw_devlink patchset.
> >
> > Greg, can you revert the whole set for 6.0, please? It's obviously
> > nowhere near tested enough to go in and I expect we'll see a bunch of
> > -stable fixups due to this if we let it remain in.
>
> What exactly is "the whole set"?  I have the default option fix queued
> up and will send that to Linus later this week (am traveling back from
> Plumbers still), but have not heard any problems about any other issues
> at all other than your report.

I stand corrected in this case, the issue on the Hifive Unmatched was
a regression due to a PWM clock change -- I just sent a patch for that
(serial driver fix).

So it seems like as long as the fw_devlink.strict=1 patch is reverted,
things are back to a working state here.

I still struggle with how the fw_devlink patchset is expected to work
though, since DT is expected to describe the hardware configuration,
and it has no knowledge of whether there are drivers that will be
bound to any referenced supplier devnodes. It's not going to work well
to assume that they will always be bound, and to add 10 second
timeouts for those cases isn't a good solution. Seems like the number
of special cases will keep adding up.

The whole design feels like it's falling short, and it's been patched
here and there to deal with the shortcomings, instead of revisiting
the full solution. (The patches are the console one, and another to
deal with nfsroot boots).

As long as it doesn't keep regressing others, I suppose the work to
redesign it can happen in-tree, but it's not usually how we try to do
it for new functionality. Especially since it's still being iterated
on (with active patch sets posted around -rc1 for improvements).

Oh, and one more thing for the future -- the main patch that changes
behavior due to dependency tracking is 2f8c3ae8288e, named "driver
core: Add wait_for_init_devices_probe helper function". It's easy to
overlook this when looking at a list of patches since it's said to
just introduce a helper.


-Olof