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From:   Geert Uytterhoeven <geert@linux-m68k.org>
Date:   Tue, 22 Nov 2022 09:25:36 +0100
Message-ID: <CAMuHMdVbzg8y2So+A=z8nUwHMoL+XKUrvoXp9QdbCnUve1_Atw@mail.gmail.com>
Subject: Re: [PATCH v2 2/7] dt-bindings: clock: renesas,r9a06g032-sysctrl: Add
 h2mode property
To:     Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Cc:     Herve Codina <herve.codina@bootlin.com>,
        Michael Turquette <mturquette@baylibre.com>,
        Stephen Boyd <sboyd@kernel.org>,
        Rob Herring <robh+dt@kernel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@linaro.org>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Magnus Damm <magnus.damm@gmail.com>,
        Gareth Williams <gareth.williams.jx@renesas.com>,
        linux-renesas-soc@vger.kernel.org, linux-clk@vger.kernel.org,
        devicetree@vger.kernel.org, linux-kernel@vger.kernel.org,
        linux-usb@vger.kernel.org,
        Thomas Petazzoni <thomas.petazzoni@bootlin.com>,
        Miquel Raynal <miquel.raynal@bootlin.com>
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Precedence: bulk

Hi Krzysztof,

On Tue, Nov 22, 2022 at 8:45 AM Krzysztof Kozlowski
<krzysztof.kozlowski@linaro.org> wrote:
> On 21/11/2022 21:46, Geert Uytterhoeven wrote:
> >> This does not change anything. Herve wrote:
> >>
> >>> probe some devices (USB host and probably others)
> >>
> >> Why some can be probed earlier and some not, if there are no
> >> dependencies? If there are dependencies, it's the same case with sysctrl
> >> touching the register bit and the USB controller touching it (as well
> >> via syscon, but that's obvious, I assume).
> >>
> >> Where is the synchronization problem?
> >
> > The h2mode bit (and probably a few other controls we haven't figured out
> > yet) in the sysctrl must be set before any of the USB devices is active.
> > Hence it's safest for the sysctrl to do this before any of the USB drivers
> > probes.
>
> Again, this does not differ from many, many of other devices. All of
> them must set something in system controller block, before they start
> operating (or at specific time). It's exactly the same everywhere.

The issue here is that there are two _different drivers_ (USB host
and device). When both are modular, and the driver that depends on the
sysctrl setting is loaded second, you have a problem: the sysctrl change
must not be done when the first driver is already using the hardware.

Hence the sysctrl driver should take care of it itself during early
initialization (it's the main clock controller, so it's a dependency
for all other I/O device drivers).

Gr{oetje,eeting}s,

                        Geert

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