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'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?
Thanks for catching that!
Best regards
Uwe
--
Pengutronix e.K. | Uwe Kleine-König |
Industrial Linux Solutions | https://www.pengutronix.de/ |
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