Messages in this thread | | | From | Nick Desaulniers <> | Date | Fri, 8 Mar 2019 10:38:11 -0800 | Subject | Re: [PATCH] pwm: img: Turn final 'else if' into 'else' in img_pwm_config |
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On Fri, Mar 8, 2019 at 12:53 AM Uwe Kleine-König <u.kleine-koenig@pengutronix.de> wrote: > > On Thu, Mar 07, 2019 at 03:36:28PM -0700, Nathan Chancellor wrote: > > When building with -Wsometimes-uninitialized, Clang warns: > > > > drivers/pwm/pwm-img.c:126:13: error: variable 'timebase' is used > > uninitialized whenever 'if' condition is false > > [-Werror,-Wsometimes-uninitialized] > > > > The final else if functions as an else; make that explicit so that Clang > > understands that timebase cannot be used uninitialized. > > > > Link: https://github.com/ClangBuiltLinux/linux/issues/400 > > Signed-off-by: Nathan Chancellor <natechancellor@gmail.com> > > --- > > drivers/pwm/pwm-img.c | 2 +- > > 1 file changed, 1 insertion(+), 1 deletion(-) > > > > diff --git a/drivers/pwm/pwm-img.c b/drivers/pwm/pwm-img.c > > index 815f5333bb8f..1cc5fbe1e1d3 100644 > > --- a/drivers/pwm/pwm-img.c > > +++ b/drivers/pwm/pwm-img.c > > @@ -123,7 +123,7 @@ static int img_pwm_config(struct pwm_chip *chip, struct pwm_device *pwm, > > } else if (mul <= max_timebase * 512) { > > div = PWM_CTRL_CFG_SUB_DIV0_DIV1; > > timebase = DIV_ROUND_UP(mul, 512); > > - } else if (mul > max_timebase * 512) { > > + } else { > > dev_err(chip->dev, > > "failed to configure timebase steps/divider value\n"); > > return -EINVAL; > > This can even be simplified further. > > From the probe function we have: > > pwm_chip->max_period_ns = NSEC_PER_SEC * 512 * max_timebase / input_clk_hz
I had trouble verifying `input_clk_hz` in the above. The divisor is `clk_get_rate(pwm->pwm_clk)`, but is it guaranteed to always be `input_clk_hz`? If so, where?
> > Then in img_pwm_config there is: > > mul = ⎡ input_clk_hz / ⎡ NSEC_PER_SEC / period_ns⎤⎤ > > (Not sure this term is the best we can come up with. The rounding > strategy looks strange because the first DIV_ROUND_UP makes mul smaller > while the second makes it bigger. This is similar to > > ⎡ input_clk_hz * period_ns / NSEC_PER_SEC ⎤ > > which is probably more exact and cheaper to calculate.) > > If we now had > > mul > max_timebase * 512 > > this results in (apart from rounding errors): > > input_clk_hz * period_ns / NSEC_PER_SEC > max_timebase * 512 > <=> period_ns > max_timebase * 512 * NSEC_PER_SEC / input_clk_hz > <=> period_ns > pwm_chip->max_period_ns > > This however is already ruled out by the first check in > img_pwm_config(). > > So if the rounding would be fixed, the else is a dead branch and could > be dropped completely.
-- Thanks, ~Nick Desaulniers
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