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

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Message-ID: <e60cd1f07f7c7515c117fa3446914c7f@agner.ch>
Date:   Mon, 06 Aug 2018 15:03:01 +0200
From:   Stefan Agner <stefan@...er.ch>
To:     Dmitry Osipenko <digetx@...il.com>
Cc:     Linus Walleij <linus.walleij@...aro.org>, 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
Subject: Re: [PATCH v1 1/2] pinctrl: tegra: Move drivers registration to
 arch_init level

On 04.08.2018 16:01, Dmitry Osipenko wrote:
> 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.
> 

Btw, just noticed this now:
GPIO driver -> arch_initcall
pinctrl driver -> subsys_initcall

And arch is before subsys. So we initialize GPIO driver first? But isn't
pinctrl required for the GPIO range?

Afaik, especially with gpio-ranges enabled, the GPIO probe will return
-EPROBE_DEFER (I think due to pinctrl_get_device_gpio_range).

So my intuition would be that it should be the other way around...

--
Stefan

>> 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.