Hi Thierry, On Thu, 18 Dec 2014 10:44:44 +0100 Thierry Reding <thierry.reding@xxxxxxxxx> wrote: > On Thu, Dec 04, 2014 at 09:10:55AM -0700, Jim Davis wrote: > > Building with the attached random configuration file, > > > > ERROR: "____ilog2_NaN" [drivers/pwm/pwm-atmel-hlcdc.ko] undefined! > > This took a while to figure out. The attached patch fixes this build > failure, though the driver should probably be fixed to avoid division by > zero, just in case. Adding Boris for visibility. Thanks for fixing this build issue. I'll propose a patch to prevent this div by 0 from happening. > > Thierry > > From 7933af1d2e5f3941d934eec88f32f5547ee218c3 Mon Sep 17 00:00:00 2001 > From: Thierry Reding <thierry.reding@xxxxxxxxx> > Date: Thu, 18 Dec 2014 10:09:42 +0100 > Subject: [PATCH] pwm: atmel-hlcdc: Depend on HAVE_CLK > > The include/linux/clk.h header defines dummy implementations for the > various clk_*() functions if HAVE_CLK is not selected to improve build > coverage in randconfig builds. > > The dummy implementation of clk_get_rate() returns 0, which causes the > Atmel HLCDC PWM driver's atmel_hlcdc_pwm_config() implementation to end > up calling: > > do_div(clk_period_ns, 0) > > On x86, do_div(n, base) will end up evaluating to this: > > n >>= ilog2(base) > > with base = 0, the implementation of ilog2() will call ____ilog2_NaN(), > which is purposely undefined and results in a linker failure: > > ERROR: "____ilog2_NaN" [drivers/pwm/pwm-atmel-hlcdc.ko] undefined! > > The implementation of do_div() checks that base is a power of 2 before > calling ilog2(). The compiler doesn't optimize this away, presumably > because is_power_of_2() is an inline function and the compiler doesn't > or can't inspect it closely enough. ilog2() being a macro it still ends > up generating the ____ilog2_NaN() because of the constant 0. > > The root of the problem is that the driver really should be checking > before possibly dividing by zero. That should eventually be fixed, but > for now just assume that the clock runs at a sensible frequency when > available. > > Reported-by: Jim Davis <jim.epost@xxxxxxxxx> > Signed-off-by: Thierry Reding <thierry.reding@xxxxxxxxx> Acked-by: Boris Brezillon <boris.brezillon@xxxxxxxxxxxxxxxxxx> > --- > drivers/pwm/Kconfig | 1 + > 1 file changed, 1 insertion(+) > > diff --git a/drivers/pwm/Kconfig b/drivers/pwm/Kconfig > index a3ecf5809634..468af1b4ca30 100644 > --- a/drivers/pwm/Kconfig > +++ b/drivers/pwm/Kconfig > @@ -53,6 +53,7 @@ config PWM_ATMEL > config PWM_ATMEL_HLCDC_PWM > tristate "Atmel HLCDC PWM support" > depends on MFD_ATMEL_HLCDC > + depends on HAVE_CLK > help > Generic PWM framework driver for the PWM output of the HLCDC > (Atmel High-end LCD Controller). This PWM output is mainly used -- Boris Brezillon, Free Electrons Embedded Linux and Kernel engineering http://free-electrons.com -- To unsubscribe from this list: send the line "unsubscribe linux-next" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
