Messages in this thread | | | Date | Thu, 01 Oct 2015 20:46:43 +0200 | From | Olliver Schinagl <> | Subject | Re: [RFC] pwm: core: unsigned or signed ints for pwm_config |
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Hey Thierry,
On 29-09-15 09:45, Thierry Reding wrote: > On Tue, Sep 29, 2015 at 09:19:27AM +0200, Olliver Schinagl wrote: >> Hey Thierry, list >> >> I'm going over the pwm core and notice that in the pwm header, duty_ns and >> period_ns is internally stored as an unsigned int. >> >> struct pwm_device { >> const char *label; >> unsigned long flags; >> unsigned int hwpwm; >> unsigned int pwm; >> struct pwm_chip *chip; >> void *chip_data; >> >> unsigned int period; >> unsigned int duty_cycle; >> enum pwm_polarity polarity; >> }; >> >> However, pwm_config takes signed ints >> int pwm_config(struct pwm_device *pwm, int duty_ns, int period_ns); >> >> So digging a little deeper in the PWM core, I see that pwm_config dissallows >> negative ints, so having them unsigned has no benefit (and technically is >> illegal) >> if (!pwm || duty_ns < 0|| period_ns= 0 || duty_ns > period_ns) >> return -EINVAL; >> >> and because (after the check) we cram the signed int into an unsigned one: >> >> pwm->duty_cycle = duty_ns; >> pwm->period = period_ns; >> >> This could end up badly when using any unsigned int larger then INT_MAX and >> thus ending up with a negative duty/period. > I don't think this is problematic because we're rejecting negative input > values and store the non-negative ones in an unsigned int, so we can > never store anything that would overflow the internal representation. > >> I haven't checked deeper if this >> is accounted for later, but would it be worth my time to convert all ints to >> unsigned ints? Since negative period and duty cycles are really not possible >> anyway? > The reason for storing them as unsigned internally is precisely because > they can never be negative. The reason why pwm_config() has plain ints > is historic. It's always been on my TODO list to convert them over to a > unsigned variant, but never high priority enough. It's also problematic > because doing so needs to modify a public API and hence requires > auditing all consumers and providers to make sure nothing breaks. > > I'm not sure if it's worth spending this effort now. Boris Brezillon > posted patches a few weeks ago to introduce an "atomic" API and that's > going to require updating all users anyway. The new API also uses the > correct types, so any effort should probably go into testing and > migrating to the new API. Thanks for saving me from doing alot of work herin ;)
Are Boris his patches merged in some dev tree of yours? I'm working on some pwm stuff too and would love to work 'with'.
Olliver > > Thierry
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