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

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Date:   Sat, 04 Aug 2018 17:01:48 +0300
From:   Dmitry Osipenko <digetx@...il.com>
To:     Linus Walleij <linus.walleij@...aro.org>
Cc:     Stefan Agner <stefan@...er.ch>,
        "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 Friday, 3 August 2018 20:24:56 MSK Linus Walleij wrote:
> 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_az
> > Oic7AA@...l.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.

Yes, it is not very good.

> 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.

Sounds interesting, maybe you could help to convert Tegra drivers to a such 
method and others will follow afterwards.

> > This should definitely go in, at least as a stop gap solution.
> 
> Agreed. (And patch applied.)

The best solution will be to fix the deferred probing, it's awkward that it 
could break suspend-resume order. Hopefully somebody with a good knowledge of 
driver/base will manage to fix it eventually.