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@xxxxxxxxxx>
> > ---
> > 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
