linux-kernel - RE: [PATCH RFC] pwm: keembay: Fix build failure with -Os

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Message-ID: <DM6PR11MB42509471531D8F009DB37E98FBE10@DM6PR11MB4250.namprd11.prod.outlook.com>
Date:   Wed, 18 Nov 2020 17:41:57 +0000
From:   "Ayyathurai, Vijayakannan" <vijayakannan.ayyathurai@...el.com>
To:     Uwe Kleine-König 
        <u.kleine-koenig@...gutronix.de>,
        Thierry Reding <thierry.reding@...il.com>
CC:     "kbuild-all@...ts.01.org" <kbuild-all@...ts.01.org>,
        lkp <lkp@...el.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "Linux Memory Management List" <linux-mm@...ck.org>,
        "kernel@...gutronix.de" <kernel@...gutronix.de>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        "Lai, Poey Seng" <poey.seng.lai@...el.com>,
        "linux-pwm@...r.kernel.org" <linux-pwm@...r.kernel.org>
Subject: RE: [PATCH RFC] pwm: keembay: Fix build failure with -Os

Hi Thierry,

> From: Uwe Kleine-König <u.kleine-koenig@...gutronix.de>
> 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@...el.com>
> > Signed-off-by: Uwe Kleine-König <u.kleine-koenig@...gutronix.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?
> 
> 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