Re: [PATCH] pwm: samsung: Fix a bit test

[Dan Carpenter <dan.carpenter@linaro.org>]

On Tue, Oct 24, 2023 at 11:11:57PM +0200, Uwe Kleine-König wrote:
> Hello Dan,
> 
> On Tue, Oct 17, 2023 at 05:04:08PM +0300, Dan Carpenter wrote:
> > This code has two problems.  First, it passes the wrong bit parameter to
> > test_bit().  Second, it mixes using PWMF_REQUESTED in test_bit() and in
> > open coded bit tests.
> > 
> > The test_bit() function takes a bit number.  In other words,
> > "if (test_bit(0, &flags))" is the equivalent of "if (flags & (1 << 0))".
> > Passing (1 << 0) to test_bit() is like writing BIT(BIT(0)).  It's a
> > double shift bug.
> > 
> > In pwm_samsung_resume() these issues mean that the flag is never set and
> > the function is essentially a no-op.
> > 
> > Fixes: 4c9548d24c0d ("pwm: samsung: Put per-channel data into driver data")
> > Signed-off-by: Dan Carpenter <dan.carpenter@linaro.org>
> > ---
> > From static analysis and not tested.
> > 
> >  drivers/pwm/pwm-samsung.c | 2 +-
> >  include/linux/pwm.h       | 4 ++--
> >  2 files changed, 3 insertions(+), 3 deletions(-)
> > 
> > diff --git a/drivers/pwm/pwm-samsung.c b/drivers/pwm/pwm-samsung.c
> > index 10fe2c13cd80..acf4a0d8d990 100644
> > --- a/drivers/pwm/pwm-samsung.c
> > +++ b/drivers/pwm/pwm-samsung.c
> > @@ -630,7 +630,7 @@ static int pwm_samsung_resume(struct device *dev)
> >  		struct pwm_device *pwm = &chip->pwms[i];
> >  		struct samsung_pwm_channel *chan = &our_chip->channel[i];
> >  
> > -		if (!(pwm->flags & PWMF_REQUESTED))
> > +		if (!test_bit(PWMF_REQUESTED, &pwm->flags))
> >  			continue;
> >  
> >  		if (our_chip->variant.output_mask & BIT(i))
> > diff --git a/include/linux/pwm.h b/include/linux/pwm.h
> > index e3b437587b32..3eee5bf367fb 100644
> > --- a/include/linux/pwm.h
> > +++ b/include/linux/pwm.h
> > @@ -41,8 +41,8 @@ struct pwm_args {
> >  };
> >  
> >  enum {
> > -	PWMF_REQUESTED = 1 << 0,
> > -	PWMF_EXPORTED = 1 << 1,
> > +	PWMF_REQUESTED = 0,
> > +	PWMF_EXPORTED  = 1,
> 
> I'd want s/  / / here. Or even not assign explicit values at all?
> 

I feel like the 0 and 1 add value.  But sure, I can remove the extra
space.  You're right that trying to align stuff is potentially going to
cause pain in the future.

> >  };
> >  
> >  /*
> 
> I'd say these are two separate issues, with the one in pwm-samsung being
> bad and the one in <linux/pwm.h> "only" ugly.
> 
> I wonder how I could get the samsung part wrong. All current usages of
> PMWF_REQUESTED (and also PWMF_EXPORTED) use test_bit (et al). Grepping
> through history pwm-pca9685.c got this wrong in a similar way for some
> time, but otherwise it was always used correctly.
> 
> The definition of the flags in <linux/pwm.h> is ugly since 
> f051c466cf69 ("pwm: Allow chips to support multiple PWMs") from 2011!
> 
> @Dan: Would you split the patch in two please?

Sure.

regards,
dan carpenter


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