linux-kernel - Re: [RFC v1 PATCH 3/3] driver: update all the code that use soc_device

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Message-ID: <CAK8P3a1Mu2F0irDDCL-50HiHth29iYFL5b7WHZ=UX6W7zzoxAg@mail.gmail.com>
Date:   Mon, 19 Apr 2021 14:16:36 +0200
From:   Arnd Bergmann <arnd@...db.de>
To:     Dominique MARTINET <dominique.martinet@...ark-techno.com>
Cc:     Geert Uytterhoeven <geert@...ux-m68k.org>,
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Subject: Re: [RFC v1 PATCH 3/3] driver: update all the code that use soc_device_match

On Mon, Apr 19, 2021 at 11:33 AM Dominique MARTINET
<dominique.martinet@...ark-techno.com> wrote:
> Geert Uytterhoeven wrote on Mon, Apr 19, 2021 at 11:03:24AM +0200:
>
> > soc_device_match() should only be used as a last resort, to identify
> > systems that cannot be identified otherwise.  Typically this is used for
> > quirks, which should only be enabled on a very specific subset of
> > systems.  IMHO such systems should make sure soc_device_match()
> > is available early, by registering their SoC device early.
>
> I definitely agree there, my suggestion to defer was only because I know
> of no other way to influence the ordering of drivers loading reliably
> and gave up on soc being init'd early.

In some cases, you can use the device_link infrastructure to deal
with dependencies between devices. Not sure if this would help
in your case, but have a look at device_link_add() etc in drivers/base/core.c

> In this particular case the problem is that since 7d981405d0fd ("soc:
> imx8m: change to use platform driver") the soc probe tries to use the
> nvmem driver for ocotp fuses for imx8m devices, which isn't ready yet.
> So soc loading gets pushed back to the end of the list because it gets
> defered and other drivers relying on soc_device_match get confused
> because they wrongly think a device doesn't match a quirk when it
> actually does.
>
> If there is a way to ensure the nvmem driver gets loaded before the soc,
> that would also solve the problem nicely, and avoid the need to mess
> with all the ~50 drivers which use it.
>
> Is there a way to control in what order drivers get loaded? Something in
> the dtb perhaps?

For built-in drivers, load order depends on the initcall level and
link order (how things are lined listed in the Makefile hierarchy).

For loadable modules, this is up to user space in the end.

Which of the drivers in this scenario are loadable modules?

        Arnd