[kbuild-all] Re: [PATCH RFC] pwm: keembay: Fix build failure with -Os

Hi Uwe, > From: Uwe Kleine-König <u.kleine-koenig(a)pengutronix.de&gt; > Sent: Monday, 16 November, 2020 5:08 PM > Subject: [PATCH RFC] pwm: keembay: Fix build failure with -Os > > The driver used this construct: > > #define KMB_PWM_LEADIN_MASK GENMASK(30, 0) > > static inline void keembay_pwm_update_bits(struct keembay_pwm > *priv, u32 mask, > u32 val, u32 offset) > { > u32 buff = readl(priv->base + offset); > > buff = u32_replace_bits(buff, val, mask); > writel(buff, priv->base + offset); > } > > ... > keembay_pwm_update_bits(priv, KMB_PWM_LEADIN_MASK, 0, > KMB_PWM_LEADIN_OFFSET(pwm- > >hwpwm)); > > With CONFIG_CC_OPTIMIZE_FOR_SIZE the compiler (here: gcc 10.2.0) this > triggers: > > In file included from /home/uwe/gsrc/linux/drivers/pwm/pwm- > keembay.c:16: > In function ‘field_multiplier’, > inlined from ‘keembay_pwm_update_bits’ at > /home/uwe/gsrc/linux/include/linux/bitfield.h:124:17: > /home/uwe/gsrc/linux/include/linux/bitfield.h:119:3: error: call to > ‘__bad_mask’ declared with attribute error: bad bitfield mask > 119 | __bad_mask(); > | ^~~~~~~~~~~~ > In function ‘field_multiplier’, > inlined from ‘keembay_pwm_update_bits’ at > /home/uwe/gsrc/linux/include/linux/bitfield.h:154:1: > /home/uwe/gsrc/linux/include/linux/bitfield.h:119:3: error: call to > ‘__bad_mask’ declared with attribute error: bad bitfield mask > 119 | __bad_mask(); > | ^~~~~~~~~~~~ > > The compiler doesn't seem to be able to notice that with field being > 0x3ffffff the expression > > if ((field | (field - 1)) & ((field | (field - 1)) + 1)) > __bad_mask(); > > can be optimized away. > > So use __always_inline and document the problem in a comment to fix > this. > > Reported-by: kernel test robot <lkp(a)intel.com&gt; > Signed-off-by: Uwe Kleine-König <u.kleine-koenig(a)pengutronix.de&gt; Thank you for spending time in resolving this build failure. I shall prepare and share the next version of patch with your approach.