Re: [PATCH RFC] pwm: keembay: Fix build failure with -Os

[Thierry Reding]

On Wed, Nov 18, 2020 at 05:41:57PM +0000, Ayyathurai, Vijayakannan wrote:
> 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.

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@xxxxxxxxx>

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

Thierry

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