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 <natechancel...@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
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.
Best regards
Uwe
--
Pengutronix e.K. | Uwe Kleine-König |
Industrial Linux Solutions | http://www.pengutronix.de/ |
