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Date:   Wed, 18 Nov 2020 19:01:22 +0100
From:   Thierry Reding <thierry.reding@gmail.com>
To:     "Ayyathurai, Vijayakannan" <vijayakannan.ayyathurai@intel.com>
Cc:     Uwe =?utf-8?Q?Kleine-K=C3=B6nig?= 
        <u.kleine-koenig@pengutronix.de>,
        "kbuild-all@lists.01.org" <kbuild-all@lists.01.org>,
        lkp <lkp@intel.com>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        Linux Memory Management List <linux-mm@kvack.org>,
        "kernel@pengutronix.de" <kernel@pengutronix.de>,
        Andy Shevchenko <andriy.shevchenko@linux.intel.com>,
        "Lai, Poey Seng" <poey.seng.lai@intel.com>,
        "linux-pwm@vger.kernel.org" <linux-pwm@vger.kernel.org>
Subject: Re: [PATCH RFC] pwm: keembay: Fix build failure with -Os
Message-ID: <20201118180122.GD3552669@ulmo>
References: <202011160303.qi5aRChY-lkp@intel.com>
 <20201116090804.206286-1-u.kleine-koenig@pengutronix.de>
 <20201118100627.chgu3tgpt3kuazsv@pengutronix.de>
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On Wed, Nov 18, 2020 at 05:41:57PM +0000, Ayyathurai, Vijayakannan wrote:
> Hi Thierry,
>=20
> > From: Uwe Kleine-K=C3=B6nig <u.kleine-koenig@pengutronix.de>
> > Subject: Re: [PATCH RFC] pwm: keembay: Fix build failure with -Os
> >=20
> > [Cc: +=3D linux-pwm which I forgot for the initial submission]
> >=20
> > Hello,
> >=20
> > On Mon, Nov 16, 2020 at 10:08:04AM +0100, Uwe Kleine-K=C3=B6nig 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 =3D readl(priv->base + offset);
> > >
> > > 		buff =3D 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 =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 bitfiel=
d 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 bitfiel=
d 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@intel.com>
> > > Signed-off-by: Uwe Kleine-K=C3=B6nig <u.kleine-koenig@pengutronix.de>
> > > ---
> > > 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?
> >=20
> > Note, this patch
> >=20
> > Fixes: cdbea243f419 ("pwm: Add PWM driver for Intel Keem Bay")
> >=20
> > so this isn't critical for v5.10.
> >=20
> > @thierry: If this is ok for you and Vijayakannan, you can squash this
> > into the original commit.
> >=20
>=20
> I am ok with Uwe approach.
> I have compiled the change and tested in Keembay board as well.

I'll take that as a Tested-by. Next time, if you go through the trouble
of testing a patch, make sure to reply with a:

Tested-by: Your Name <your@email.com>

So that patchwork can pick that up and credit you for it.

Thierry

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