linux-kernel - Re: [PATCH] pinctrl: generic: Avoid several implicit enum conversions

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Date:   Tue, 25 Sep 2018 09:23:09 -0700
From:   Nick Desaulniers <ndesaulniers@...gle.com>
To:     Nathan Chancellor <natechancellor@...il.com>
Cc:     linus.walleij@...aro.org, linux-gpio@...r.kernel.org,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] pinctrl: generic: Avoid several implicit enum conversions

On Tue, Sep 25, 2018 at 9:15 AM Nathan Chancellor
<natechancellor@...il.com> wrote:
>
> On Tue, Sep 25, 2018 at 12:58:16PM +0200, Linus Walleij wrote:
> > On Tue, Sep 25, 2018 at 8:19 AM Nathan Chancellor
> > <natechancellor@...il.com> wrote:
> >
> > > Clang warns when one enumerated type is implicitly converted to another,
> > > which happens several times in the pinctrl drivers for a few reasons:
> > >
> > > * The PCONFDUMP macro, which sets the param member in pin_config_item.
> > > * The pinconf_generic_params structure, which is used by drivers to
> > >   configure their bindings, which has a param member like pin_config_item.
> > > * The pinconf_to_config_packed, which takes either the generic enum
> > >   pin_config_param or a specialized one.
> > >
> > > Drivers are allowed to extend this enumerated type because of the gap
> > > betweem PIN_CONFIG_END and PIN_CONFIG_MAX. Make it clear to Clang that
> > > this is allowed by changing param's type in all of these instances to
> > > int so no conversion needs to happen.
> > >
> > > Link: https://github.com/ClangBuiltLinux/linux/issues/138
> > > Signed-off-by: Nathan Chancellor <natechancellor@...il.com>
> >
> > I'm not superhappy about this because that enum is great for readability,
> > even if the static syntax checker is unhappy.
> >
> > If we can't have an enum here I would argue that we can just as well
> > remove the enum altogether and just use #define for the config
> > parameters, would you agree?
> >
> > Yours,
> > Linus Walleij
>
> Hi Linus,
>
> I see no reason to get rid of the enums. All this patch should do is
> silence Clang's warnings because there is no other way to tell it that
> this construct is okay except for changing the parameter/member type to
> int (so no conversion needs to happen) or an explicit cast, which will
> result in more noise in my opinion since this warning happens at least
> 10-15 times in the pinctrl drivers. There's no fundamental change to
> how the enums are used.
>
> See these other commits for similar fixes:
>
> 3eb95feac113 ("mm/zsmalloc.c: change stat type parameter to int")
> 04fecbf51b3c ("mm: memcontrol: use int for event/state parameter in several functions")
>
> Cheers!
> Nathan

That or all of the call sites should have explicit casts to the base enum.

-- 
Thanks,
~Nick Desaulniers