Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
MIME-Version: 1.0
References: <20221114111513.1436165-1-herve.codina@bootlin.com>
 <20221114111513.1436165-3-herve.codina@bootlin.com> <a1a7fdf4-2608-d6c9-7c7a-f8e8fae3a742@linaro.org>
 <c9a77262-f137-21d9-58af-eb4efb8aadbf@linaro.org> <20221115150417.513955a7@bootlin.com>
 <20221118112349.7f09eefb@bootlin.com> <d9bd5075-9d06-888d-36a9-911e2d7ec5af@linaro.org>
 <20221121165921.559d6538@bootlin.com> <4e54bfb4-bb67-73b8-f58f-56797c5925d3@linaro.org>
 <CAMuHMdU=-ZUzHSb0Z8P3wsLK9cgGVCPdMi6AcjTH23tUQEeEBA@mail.gmail.com>
 <a3e1332e-fc15-8a78-0ddd-6d5b26197f11@linaro.org> <CAMuHMdXzqZB4sKMmroriq5oPp7z=yXiHk=+eQKwSyPhNbYqgYA@mail.gmail.com>
 <1f12883b-1e37-7f2b-f9e9-c8bad290a133@linaro.org> <CAMuHMdVbzg8y2So+A=z8nUwHMoL+XKUrvoXp9QdbCnUve1_Atw@mail.gmail.com>
 <191a7f3e-0733-8058-5829-fe170a06dd5a@linaro.org> <CAMuHMdV1Y4Ldq2Hu5X8awTOWYTHq4DPYWCMkyg-9TQY=DaxREg@mail.gmail.com>
 <978fb5a1-64f3-7ee6-3e98-1e31b8b6a88b@linaro.org>
In-Reply-To: <978fb5a1-64f3-7ee6-3e98-1e31b8b6a88b@linaro.org>
From:   Geert Uytterhoeven <geert@linux-m68k.org>
Date:   Tue, 22 Nov 2022 11:26:07 +0100
Message-ID: <CAMuHMdXMoYnCHBmSwgzriOhL=EEibzsUsMKnnMK_9sZ20339Bw@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>
Content-Type: text/plain; charset="UTF-8"
Precedence: bulk

Hi Krzysztof,

On Tue, Nov 22, 2022 at 11:23 AM Krzysztof Kozlowski
<krzysztof.kozlowski@linaro.org> wrote:
> On 22/11/2022 10:01, Geert Uytterhoeven wrote:
> >>>>> 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).
> >>
> >> I assumed you have there bit for the first device (which can switch
> >> between USB host and USB device) to choose appropriate mode. The
> >> bindings also expressed this - "the USBs are". Never said anything about
> >> dependency between these USBs.
> >>
> >> Are you saying that the mode for first device cannot be changed once the
> >> second device (which is only host) is started? IOW, the mode setup must
> >> happen before any of these devices are started?
> >
> > Exactly.
> >
> >> Anyway with sysctrl approach you will have dependency and you cannot
> >> rely on clock provider-consumer relationship to order that dependency.
> >> What if you make all clocks on and do not take any clocks in USB device?
> >
> > Enabling the clocks does not have anything to do with this ordering.
>
> That was the argument from Herve, that ordering is guaranteed by clocks.
>
> > Clock consumers that are part of the clock domain are probed after
> > clock providers.  If the clock is missing, that would be an incorrect
> > description in DTS.
>
> If not clocks, what else is guaranteeing the ordering? You did not
> express it in DT.

clocks and power-domains

And if not clocks and power-domains... Oops, we didn't express in DT
that the SoC needs to be powered at all ;-)

Can we please stop this pointless discussion?
Thanks!

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