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Date:   Wed, 18 Nov 2020 19:00:14 +0100
From:   Thierry Reding <thierry.reding@gmail.com>
To:     Uwe =?utf-8?Q?Kleine-K=C3=B6nig?= <u.kleine-koenig@pengutronix.de>
Cc:     Vijayakannan Ayyathurai <vijayakannan.ayyathurai@intel.com>,
        kbuild-all@lists.01.org,
        Linux Memory Management List <linux-mm@kvack.org>,
        "Lai, Poey Seng" <poey.seng.lai@intel.com>,
        "Vineetha G. Jaya Kumaran" <vineetha.g.jaya.kumaran@intel.com>,
        Andy Shevchenko <andriy.shevchenko@linux.intel.com>,
        linux-kernel@vger.kernel.org, kernel@pengutronix.de,
        kernel test robot <lkp@intel.com>
Subject: Re: [PATCH RFC] pwm: keembay: Fix build failure with -Os
Message-ID: <20201118180014.GC3552669@ulmo>
References: <202011160303.qi5aRChY-lkp@intel.com>
 <20201116090804.206286-1-u.kleine-koenig@pengutronix.de>
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On Mon, Nov 16, 2020 at 10:08:04AM +0100, Uwe Kleine-K=C3=B6nig wrote:
> The driver used this construct:
>=20
> 	#define KMB_PWM_LEADIN_MASK             GENMASK(30, 0)
>=20
> 	static inline void keembay_pwm_update_bits(struct keembay_pwm *priv, u32=
 mask,
> 						   u32 val, u32 offset)
> 	{
> 		u32 buff =3D readl(priv->base + offset);
>=20
> 		buff =3D u32_replace_bits(buff, val, mask);
> 		writel(buff, priv->base + offset);
> 	}
>=20
> 	...
> 	keembay_pwm_update_bits(priv, KMB_PWM_LEADIN_MASK, 0,
> 					KMB_PWM_LEADIN_OFFSET(pwm->hwpwm));
>=20
> With CONFIG_CC_OPTIMIZE_FOR_SIZE the compiler (here: gcc 10.2.0) this
> triggers:
>=20
> 	In file included from /home/uwe/gsrc/linux/drivers/pwm/pwm-keembay.c:16:
> 	In function =E2=80=98field_multiplier=E2=80=99,
> 	    inlined from =E2=80=98keembay_pwm_update_bits=E2=80=99 at /home/uwe/=
gsrc/linux/include/linux/bitfield.h:124:17:
> 	/home/uwe/gsrc/linux/include/linux/bitfield.h:119:3: error: call to =E2=
=80=98__bad_mask=E2=80=99 declared with attribute error: bad bitfield mask
> 	  119 |   __bad_mask();
> 	      |   ^~~~~~~~~~~~
> 	In function =E2=80=98field_multiplier=E2=80=99,
> 	    inlined from =E2=80=98keembay_pwm_update_bits=E2=80=99 at /home/uwe/=
gsrc/linux/include/linux/bitfield.h:154:1:
> 	/home/uwe/gsrc/linux/include/linux/bitfield.h:119:3: error: call to =E2=
=80=98__bad_mask=E2=80=99 declared with attribute error: bad bitfield mask
> 	  119 |   __bad_mask();
> 	      |   ^~~~~~~~~~~~
>=20
> The compiler doesn't seem to be able to notice that with field being
> 0x3ffffff the expression
>=20
> 	if ((field | (field - 1)) & ((field | (field - 1)) + 1))
> 		__bad_mask();
>=20
> can be optimized away.
>=20
> So use __always_inline and document the problem in a comment to fix
> this.
>=20
> Reported-by: kernel test robot <lkp@intel.com>
> Signed-off-by: Uwe Kleine-K=C3=B6nig <u.kleine-koenig@pengutronix.de>
> ---
> Hello,
>=20
> I'm not sure this is the right fix. Maybe the bitfield stuff can be
> changed somehow to make this problem go away, too?
>=20
> Best regards
> Uwe
>=20
>  drivers/pwm/pwm-keembay.c | 7 ++++++-
>  1 file changed, 6 insertions(+), 1 deletion(-)

Applied, thanks.

Thierry

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