Re: [PATCH] watchdog: coh901327: add COMMON_CLK dependency

From: Guenter Roeck <linux@roeck-us.net>
To: Nick Desaulniers <ndesaulniers@google.com>
Cc: Arnd Bergmann <arnd@kernel.org>,
	Wim Van Sebroeck <wim@linux-watchdog.org>,
	Nathan Chancellor <natechancellor@gmail.com>,
	Arnd Bergmann <arnd@arndb.de>,
	linux-watchdog@vger.kernel.org,
	LKML <linux-kernel@vger.kernel.org>,
	clang-built-linux <clang-built-linux@googlegroups.com>
Subject: Re: [PATCH] watchdog: coh901327: add COMMON_CLK dependency
Date: Thu, 10 Dec 2020 16:16:59 -0800	[thread overview]
Message-ID: <20201211001659.GH259082@roeck-us.net> (raw)
In-Reply-To: <CAKwvOd=i6DFLrPAe5KihT+ZK-nFZ+L7troC300q-9Jpa=i4Fqg@mail.gmail.com>

On Thu, Dec 10, 2020 at 03:00:30PM -0800, Nick Desaulniers wrote:
> On Thu, Dec 3, 2020 at 2:34 PM Arnd Bergmann <arnd@kernel.org> wrote:
> >
> > From: Arnd Bergmann <arnd@arndb.de>
> >
> > clang produces a build failure in configurations without COMMON_CLK
> > when a timeout calculation goes wrong:
> >
> > arm-linux-gnueabi-ld: drivers/watchdog/coh901327_wdt.o: in function `coh901327_enable':
> > coh901327_wdt.c:(.text+0x50): undefined reference to `__bad_udelay'
> 
> Isn't a linkage failure against __bad_udelay supposed to be
> interpreted as a value too large being passed to udelay()? IIRC, this
> was an issue for someone building an Apple touchpad driver with Clang
> at -O3...you sent a fix for that:
> https://github.com/ClangBuiltLinux/linux/issues/678,
> https://git.kernel.org/pub/scm/linux/kernel/git/groeck/linux-staging.git/commit/?id=fff2d0f701e6753591609739f8ab9be1c8e80ebb.

The problem is likely that clk_get_rate() returns a constant 0,
which in the real world would end up in a divide by 0 crash.
An alternative might be be to add

	freq = clk_get_rate(clk);
-->	if (freq == 0)
-->		return;

but I don't know if that would really be worth the effort.
I prefer the current fix.

Guenter

> 
> >
> > Add a Kconfig dependency to only do build testing when COMMON_CLK
> > is enabled.
> >
> > Fixes: da2a68b3eb47 ("watchdog: Enable COMPILE_TEST where possible")
> > Signed-off-by: Arnd Bergmann <arnd@arndb.de>
> > ---
> >  drivers/watchdog/Kconfig | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/drivers/watchdog/Kconfig b/drivers/watchdog/Kconfig
> > index 8bdbd125821b..32fa6de7b820 100644
> > --- a/drivers/watchdog/Kconfig
> > +++ b/drivers/watchdog/Kconfig
> > @@ -631,7 +631,7 @@ config SUNXI_WATCHDOG
> >
> >  config COH901327_WATCHDOG
> >         bool "ST-Ericsson COH 901 327 watchdog"
> > -       depends on ARCH_U300 || (ARM && COMPILE_TEST)
> > +       depends on ARCH_U300 || (ARM && COMMON_CLK && COMPILE_TEST)
> >         default y if MACH_U300
> >         select WATCHDOG_CORE
> >         help
> > --
> > 2.27.0
> >
> 
> 
> -- 
> Thanks,
> ~Nick Desaulniers