[kbuild-all] Re: [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; --- Hello, I'm not sure this is the right fix. Maybe the bitfield stuff can be changed somehow to make this problem go away, too?