Hi Thierry,
> From: Uwe Kleine-König <u.kleine-koenig@xxxxxxxxxxxxxx>
> Subject: Re: [PATCH RFC] pwm: keembay: Fix build failure with -Os
>
> [Cc: += linux-pwm which I forgot for the initial submission]
>
> Hello,
>
> On Mon, Nov 16, 2020 at 10:08:04AM +0100, Uwe Kleine-König wrote:
> > 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@xxxxxxxxx>
> > Signed-off-by: Uwe Kleine-König <u.kleine-koenig@xxxxxxxxxxxxxx>
> > ---
> > 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?
>
> Note, this patch
>
> Fixes: cdbea243f419 ("pwm: Add PWM driver for Intel Keem Bay")
>
> so this isn't critical for v5.10.
>
> @thierry: If this is ok for you and Vijayakannan, you can squash this
> into the original commit.
>
I am ok with Uwe approach.
I have compiled the change and tested in Keembay board as well.
> Best regards
> Uwe
>
> --
> Pengutronix e.K. | Uwe Kleine-König |
> Industrial Linux Solutions | https://www.pengutronix.de/ |
Thanks,
Vijay
