linux-kernel - Re: [PATCH v1 1/2] pinctrl: tegra: Move drivers registration to arch

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Message-ID: <CACRpkda+t=0aJMSKre+U-GHN2d47pV3b_g13PcinXScP_UX5Ng@mail.gmail.com>
Date:   Fri, 3 Aug 2018 19:24:56 +0200
From:   Linus Walleij <linus.walleij@...aro.org>
To:     Stefan Agner <stefan@...er.ch>
Cc:     Dmitry Osipenko <digetx@...il.com>,
        "thierry.reding@...il.com" <thierry.reding@...il.com>,
        Jon Hunter <jonathanh@...dia.com>,
        Marcel Ziswiler <marcel@...wiler.com>,
        linux-tegra@...r.kernel.org,
        "open list:GPIO SUBSYSTEM" <linux-gpio@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v1 1/2] pinctrl: tegra: Move drivers registration to
 arch_init level

On Thu, Aug 2, 2018 at 1:31 PM Stefan Agner <stefan@...er.ch> wrote:

> A while back at least using those init lists were not well received even
> for GPIO/pinctrl drivers:
>
> https://lore.kernel.org/lkml/CACRpkdYk0zW12qNXgOstTLmdVDYacu0Un+8quTN+J_azOic7AA@mail.gmail.com/T/#mf0596982324a6489b5537b0531ac5aed60a316ba

You shouldn't listen too much to that guy he's not trustworthy.

> I still think we should make an exception for GPIO/pinctrl and use
> earlier initcalls. Platform GPIO/pinctrl drivers provide basic
> infrastructure often used by many other drivers, we want to have them
> loaded early. It avoids unnecessary EPROBE_DEFER and hence probably even
> boots faster.

When we have the pin control and GPIO at different initlevels it makes me
uneasy because I feel we have implicit init dependencies that seem more
than a little fragile.

My recent thinking has involved the component method used in DRM drivers
such as drivers/gpu/drm/vc4/vc4_drv.c where a few different component
subdrivers are linked together at bind time (not probe time!) into a master
component.

Rob was no big fan of this but the DRM people like it and I was thinking to
make a try at it.

This way we could at least probe and bind the pin control and GPIO drivers
at the *same* initlevel and express the dependencies between them
somewhat.

> This should definitely go in, at least as a stop gap solution.

Agreed. (And patch applied.)

Yours,
Linus Walleij