linux-kernel - Re: [PATCH 1/3] gpio: mxc: Support module build

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Date:   Thu, 16 Jul 2020 15:54:55 +0200
From:   Linus Walleij <linus.walleij@...aro.org>
To:     Anson Huang <anson.huang@....com>
Cc:     Russell King <linux@...linux.org.uk>,
        Shawn Guo <shawnguo@...nel.org>,
        Sascha Hauer <s.hauer@...gutronix.de>,
        Sascha Hauer <kernel@...gutronix.de>,
        Fabio Estevam <festevam@...il.com>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>,
        Bartosz Golaszewski <bgolaszewski@...libre.com>,
        "oleksandr.suvorov@...adex.com" <oleksandr.suvorov@...adex.com>,
        Adam Ford <aford173@...il.com>,
        Andreas Kemnade <andreas@...nade.info>,
        "hverkuil-cisco@...all.nl" <hverkuil-cisco@...all.nl>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        Leo Li <leoyang.li@....com>, Vinod Koul <vkoul@...nel.org>,
        Geert Uytterhoeven <geert+renesas@...der.be>,
        Olof Johansson <olof@...om.net>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "open list:GPIO SUBSYSTEM" <linux-gpio@...r.kernel.org>,
        dl-linux-imx <linux-imx@....com>
Subject: Re: [PATCH 1/3] gpio: mxc: Support module build

On Wed, Jul 15, 2020 at 4:44 AM Anson Huang <anson.huang@....com> wrote:

> > Subject: RE: [PATCH 1/3] gpio: mxc: Support module build
> >
> > Hi, Linus
> >
> > > Subject: Re: [PATCH 1/3] gpio: mxc: Support module build
> > >
> > > On Wed, Jul 8, 2020 at 1:28 AM Anson Huang <Anson.Huang@....com>
> > > wrote:
> > >
> > > >  subsys_initcall(gpio_mxc_init);
> > > > +
> > > > +MODULE_AUTHOR("Shawn Guo <shawn.guo@...aro.org>");
> > > > +MODULE_DESCRIPTION("i.MX GPIO Driver"); MODULE_LICENSE("GPL");
> > >
> > > You are making this modualrizable but keeping the subsys_initcall(),
> > > which doesn't make very much sense. It is obviously not necessary to
> > > do this probe at subsys_initcall() time, right?
> > >
> >
> > If building it as module, the subsys_initcall() will be equal to module_init(), I
> > keep it unchanged is because I try to make it identical when built-in, since
> > most of the config will still have it built-in, except the Android GKI support.
> > Does it make sense?
> >
> > > Take this opportunity to convert the driver to use
> > > module_platform_driver() as well.
> >
> > If you think it has to be or it is better to use module_platform_driver(), I will do
> > it in V2.
>
> I tried to replace the subsys_initcall() with module_platform_driver(), but met issue
> about " register_syscore_ops(&mxc_gpio_syscore_ops);" which is called in gpio_mxc_init()
> function, this function should be called ONLY once, moving it to .probe function is NOT
> working, so we may need to keep the gpio_mxc_init(), that is another reason that we may
> need to keep subsys_initcall()?

This looks a bit dangerous to keep like this while allowing this
code to be used from a module.

What happens if you insmod and rmmod this a few times, really?
How is this tested?

This is not really modularized if that isn't working, just that modprobing
once works isn't real modularization IMO, it seems more like a
quick and dirty way to get Androids GKI somewhat working with the module
while not properly making the module a module.

You need input from the driver maintainers on how to handle this.

Yours,
Linus Walleij