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authorThierry Reding <thierry.reding@gmail.com>2014-12-18 12:09:42 +0300
committerThierry Reding <thierry.reding@gmail.com>2015-01-30 14:15:58 +0300
commitd2048c49152a414efcf8b2696896bc8803ef2f1e (patch)
tree32838cb723c326344bbdc03463ac89110af11769 /drivers/pwm
parent97bf6af1f928216fd6c5a66e8a57bfa95a659672 (diff)
downloadlinux-d2048c49152a414efcf8b2696896bc8803ef2f1e.tar.xz
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@gmail.com> Acked-by: Boris Brezillon <boris.brezillon@free-electrons.com> Signed-off-by: Thierry Reding <thierry.reding@gmail.com>
Diffstat (limited to 'drivers/pwm')
-rw-r--r--drivers/pwm/Kconfig1
1 files changed, 1 insertions, 0 deletions
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