linux-kernel - Re: [PATCH 01/10] reset: ath79: add driver Kconfig option

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Date:   Wed, 24 Aug 2016 22:06:04 +0200
From:   Arnd Bergmann <arnd@...db.de>
To:     linux-arm-kernel@...ts.infradead.org
Cc:     Masahiro Yamada <yamada.masahiro@...ionext.com>,
        Axel Lin <axel.lin@...ics.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Hans de Goede <hdegoede@...hat.com>,
        Alban Bedel <albeu@...e.fr>,
        Philipp Zabel <p.zabel@...gutronix.de>,
        Maxime Ripard <maxime.ripard@...e-electrons.com>,
        Lee Jones <lee.jones@...aro.org>
Subject: Re: [PATCH 01/10] reset: ath79: add driver Kconfig option

On Thursday, August 25, 2016 3:18:55 AM CEST Masahiro Yamada wrote:
> Hi Arnd,
> 
> 
> 2016-08-25 0:51 GMT+09:00 Arnd Bergmann <arnd@...db.de>:
> > On Wednesday, August 24, 2016 3:28:53 PM CEST Philipp Zabel wrote:
> >>  if RESET_CONTROLLER
> >>
> >> +config RESET_ATH79
> >> +       bool "AR71xx Reset Driver" if COMPILE_TEST
> >> +       default ATH79
> >> +       help
> >> +         This enables the ATH79 reset controller driver that supports the
> >> +         AR71xx SoC reset controller.
> >> +
> >>
> >
> > Nice series!
> >
> > Just note that there is one possible problem with COMPILE_TEST
> > when the platforms are enabled, as you can then disable a driver
> > that is normally there, and that can in turn cause problems in
> > rare cases, e.g. when the driver has a global function that is
> > called from platform code. I don't know if any of the drivers
> > do that, but if they do, you'd have to use
> >
> > config RESET_ATH79
> >        bool "AR71xx Reset Driver" if COMPILE_TEST && !ATH79
> >        default ATH79
> >
> > to ensure that it's impossible to disable the driver on platforms
> > that require it.
> 
> Hmm,
> Can we do this only when we really have to do so?
> I think we should not care about such a rare case that may not happen.
> 
> Let's start with only "if COMPILE_TEST",
> and take a look at it if a build error is detected.
> 
> Anyway, depending on platform code is a sign of weird implementation.
> 
> It might be better to find a potential issue rather than hide it.
> 
> 
> 

I just checked the object files in an allyesconfig build and found
one instance:

arch/arm/mach-sunxi/sunxi.c:extern void __init sun6i_reset_init(void);
arch/arm/mach-sunxi/sunxi.c:            sun6i_reset_init();
drivers/reset/reset-sunxi.c:void __init sun6i_reset_init(void)

We should definitely make sure this one is handled right, and maybe
check the source code for other instances.

	Arnd