| Message ID | 1465403688-17098-2-git-send-email-boris.brezillon@free-electrons.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
On Wed, Jun 08, 2016 at 06:34:36PM +0200, Boris Brezillon wrote: > The pwm_prepare_new_state() helper prepares a new state object > containing the current PWM state except for the polarity and period > fields which are set to the reference values. > This is particurly useful for PWM users who want to apply a new > duty-cycle expressed relatively to the reference period without > changing the enable state. > > The PWM framework expect PWM users to configure the duty cycle in > nanosecond, but most users just want to express this duty cycle > relatively to the period value (i.e. duty_cycle = 33% of the period). > Add pwm_{get,set}_relative_duty_cycle() helpers to ease this kind of > conversion. This looks pretty useful and good, though I think these could be two separate patches. A couple of suggestions on wording and such below. > Signed-off-by: Boris Brezillon <boris.brezillon@free-electrons.com> > --- > include/linux/pwm.h | 81 +++++++++++++++++++++++++++++++++++++++++++++++++++++ > 1 file changed, 81 insertions(+) > > diff --git a/include/linux/pwm.h b/include/linux/pwm.h > index 17018f3..e09babf 100644 > --- a/include/linux/pwm.h > +++ b/include/linux/pwm.h > @@ -148,6 +148,87 @@ static inline void pwm_get_args(const struct pwm_device *pwm, > } > > /** > + * pwm_prepare_new_state() - prepare a new state to be applied with > + * pwm_apply_state() This is weirdly indented. > + * @pwm: PWM device > + * @state: state to fill with the prepared PWM state > + * > + * This functions prepares a state that can later be tweaked and applied > + * to the PWM device with pwm_apply_state(). This is a convenient function > + * that first retrieves the current PWM state and the replaces the period > + * and polarity fields with the reference values defined in pwm->args. > + * Once the new state is created you can adjust the ->enable and ->duty_cycle "created" has the connotation of allocating. Perhaps: "Once the function returns, you can adjust the ->enabled and ->duty_cycle fields according to your needs before calling pwm_apply_state()."? Also note that the field is called ->enabled. > + * according to your need before calling pwm_apply_state(). Maybe mention that the ->duty_cycle field is explicitly zeroed. Then again, do we really need it? If users are going to overwrite it anyway, do we even need to bother? I suppose it makes some sense because the current duty cycle is stale when the ->period gets set to the value from args. I think the documentation should mention this in some way. > + */ > +static inline void pwm_prepare_new_state(const struct pwm_device *pwm, > + struct pwm_state *state) Perhaps choose a shorter name, such as: pwm_init_state()? > +{ > + struct pwm_args args; > + > + /* First get the current state. */ > + pwm_get_state(pwm, state); > + > + /* Then fill it with the reference config */ > + pwm_get_args(pwm, &args); > + > + state->period = args.period; > + state->polarity = args.polarity; > + state->duty_cycle = 0; > +} > + > +/** > + * pwm_get_relative_duty_cycle() - Get a relative duty_cycle value > + * @state: the PWM state to extract period and duty_cycle from > + * @scale: the scale you want to use for you relative duty_cycle value Other kerneldoc comments in this file don't prefix the description with "the". Also, perhaps the following descriptions would be slightly less confusing: @state: PWM state to extract the duty cycle from We don't extract (i.e. return) period from the state, so it's a little confusing to mention it here. @scale: scale in which to return the relative duty cycle This is slightly more explicit in that it says what the returned duty cycle will be in. Perhaps as an alternative: @scale: target scale of the relative duty cycle > + * > + * This functions converts the absolute duty_cycle stored in @state > + * (expressed in nanosecond) into a relative value. Perhaps: "... into a value relative to the period."? > + * For example if you want to get the duty_cycle expressed in nanosecond, The example below would give you the duty cycle in percent, not nanoseconds, right? > + * call: > + * > + * pwm_get_state(pwm, &state); > + * duty = pwm_get_relative_duty_cycle(&state, 100); > + */ > +static inline unsigned int > +pwm_get_relative_duty_cycle(const struct pwm_state *state, unsigned int scale) > +{ > + if (!state->period) > + return 0; > + > + return DIV_ROUND_CLOSEST_ULL((u64)state->duty_cycle * scale, > + state->period); > +} > + > +/** > + * pwm_set_relative_duty_cycle() - Set a relative duty_cycle value > + * @state: the PWM state to fill > + * @val: the relative duty_cycle value > + * @scale: the scale you use for you relative duty_cycle value "scale in which @duty_cycle is expressed"? > + * > + * This functions converts a relative duty_cycle stored into an absolute > + * one (expressed in nanoseconds), and put the result in state->duty_cycle. > + * For example if you want to change configure a 50% duty_cycle, call: > + * > + * pwm_prepare_new_state(pwm, &state); > + * pwm_set_relative_duty_cycle(&state, 50, 100); > + * pwm_apply_state(pwm, &state); > + */ > +static inline void > +pwm_set_relative_duty_cycle(struct pwm_state *state, unsigned int val, Any reason why we can't call "val" "duty_cycle"? That's what it is, after all. > + unsigned int scale) > +{ > + if (!scale) > + return; > + > + /* Make sure we don't have duty_cycle > period */ > + if (val > scale) > + val = scale; Can we return -EINVAL for both of the above checks? I don't like silently clamping the duty cycle that the user passed in. Thierry
Hi Thierry, On Fri, 10 Jun 2016 17:21:09 +0200 Thierry Reding <thierry.reding@gmail.com> wrote: > On Wed, Jun 08, 2016 at 06:34:36PM +0200, Boris Brezillon wrote: > > The pwm_prepare_new_state() helper prepares a new state object > > containing the current PWM state except for the polarity and period > > fields which are set to the reference values. > > This is particurly useful for PWM users who want to apply a new > > duty-cycle expressed relatively to the reference period without > > changing the enable state. > > > > The PWM framework expect PWM users to configure the duty cycle in > > nanosecond, but most users just want to express this duty cycle > > relatively to the period value (i.e. duty_cycle = 33% of the period). > > Add pwm_{get,set}_relative_duty_cycle() helpers to ease this kind of > > conversion. > > This looks pretty useful and good, though I think these could be two > separate patches. A couple of suggestions on wording and such below. Sure, I can split those changes. > > > Signed-off-by: Boris Brezillon <boris.brezillon@free-electrons.com> > > --- > > include/linux/pwm.h | 81 +++++++++++++++++++++++++++++++++++++++++++++++++++++ > > 1 file changed, 81 insertions(+) > > > > diff --git a/include/linux/pwm.h b/include/linux/pwm.h > > index 17018f3..e09babf 100644 > > --- a/include/linux/pwm.h > > +++ b/include/linux/pwm.h > > @@ -148,6 +148,87 @@ static inline void pwm_get_args(const struct pwm_device *pwm, > > } > > > > /** > > + * pwm_prepare_new_state() - prepare a new state to be applied with > > + * pwm_apply_state() > > This is weirdly indented. I'll fix the indentation. > > > + * @pwm: PWM device > > + * @state: state to fill with the prepared PWM state > > + * > > + * This functions prepares a state that can later be tweaked and applied > > + * to the PWM device with pwm_apply_state(). This is a convenient function > > + * that first retrieves the current PWM state and the replaces the period > > + * and polarity fields with the reference values defined in pwm->args. > > + * Once the new state is created you can adjust the ->enable and ->duty_cycle > > "created" has the connotation of allocating. Perhaps: "Once the function > returns, you can adjust the ->enabled and ->duty_cycle fields according > to your needs before calling pwm_apply_state()."? Okay. > > Also note that the field is called ->enabled. > > > + * according to your need before calling pwm_apply_state(). > > Maybe mention that the ->duty_cycle field is explicitly zeroed. Then > again, do we really need it? If users are going to overwrite it anyway, > do we even need to bother? I suppose it makes some sense because the > current duty cycle is stale when the ->period gets set to the value from > args. I think the documentation should mention this in some way. Yes, if we keep the current duty_cycle it can exceed the period value. I'm fine dropping the ->duty_cycle = 0 assignment and documenting the behavior. > > > + */ > > +static inline void pwm_prepare_new_state(const struct pwm_device *pwm, > > + struct pwm_state *state) > > Perhaps choose a shorter name, such as: pwm_init_state()? Sure. > > > +{ > > + struct pwm_args args; > > + > > + /* First get the current state. */ > > + pwm_get_state(pwm, state); > > + > > + /* Then fill it with the reference config */ > > + pwm_get_args(pwm, &args); > > + > > + state->period = args.period; > > + state->polarity = args.polarity; > > + state->duty_cycle = 0; > > +} > > + > > +/** > > + * pwm_get_relative_duty_cycle() - Get a relative duty_cycle value > > + * @state: the PWM state to extract period and duty_cycle from > > + * @scale: the scale you want to use for you relative duty_cycle value > > Other kerneldoc comments in this file don't prefix the description with > "the". > > Also, perhaps the following descriptions would be slightly less > confusing: > > @state: PWM state to extract the duty cycle from Agreed. > > We don't extract (i.e. return) period from the state, so it's a little > confusing to mention it here. > > @scale: scale in which to return the relative duty cycle > > This is slightly more explicit in that it says what the returned duty > cycle will be in. Perhaps as an alternative: > > @scale: target scale of the relative duty cycle I'll go for this one. > > > + * > > + * This functions converts the absolute duty_cycle stored in @state > > + * (expressed in nanosecond) into a relative value. > > Perhaps: "... into a value relative to the period."? Okay. > > > + * For example if you want to get the duty_cycle expressed in nanosecond, > > The example below would give you the duty cycle in percent, not > nanoseconds, right? Absolutely. I'll fix that. > > > + * call: > > + * > > + * pwm_get_state(pwm, &state); > > + * duty = pwm_get_relative_duty_cycle(&state, 100); > > + */ > > +static inline unsigned int > > +pwm_get_relative_duty_cycle(const struct pwm_state *state, unsigned int scale) > > +{ > > + if (!state->period) > > + return 0; > > + > > + return DIV_ROUND_CLOSEST_ULL((u64)state->duty_cycle * scale, > > + state->period); > > +} > > + > > +/** > > + * pwm_set_relative_duty_cycle() - Set a relative duty_cycle value > > + * @state: the PWM state to fill > > + * @val: the relative duty_cycle value > > + * @scale: the scale you use for you relative duty_cycle value > > "scale in which @duty_cycle is expressed"? Yep. > > > + * > > + * This functions converts a relative duty_cycle stored into an absolute > > + * one (expressed in nanoseconds), and put the result in state->duty_cycle. > > + * For example if you want to change configure a 50% duty_cycle, call: > > + * > > + * pwm_prepare_new_state(pwm, &state); > > + * pwm_set_relative_duty_cycle(&state, 50, 100); > > + * pwm_apply_state(pwm, &state); > > + */ > > +static inline void > > +pwm_set_relative_duty_cycle(struct pwm_state *state, unsigned int val, > > Any reason why we can't call "val" "duty_cycle"? That's what it is, > after all. Nope, I'll switch to duty_cycle. > > > + unsigned int scale) > > +{ > > + if (!scale) > > + return; > > + > > + /* Make sure we don't have duty_cycle > period */ > > + if (val > scale) > > + val = scale; > > Can we return -EINVAL for both of the above checks? I don't like > silently clamping the duty cycle that the user passed in. I'm fine returning -EINVAL in this case. Thanks for rewording some of my sentences and reviewing the patch. Regards, Boris
On Fri, Jun 10, 2016 at 06:29:42PM +0200, Boris Brezillon wrote: > On Fri, 10 Jun 2016 17:21:09 +0200, Thierry Reding <thierry.reding@gmail.com> wrote: > > On Wed, Jun 08, 2016 at 06:34:36PM +0200, Boris Brezillon wrote: [...] > > > + * according to your need before calling pwm_apply_state(). > > > > Maybe mention that the ->duty_cycle field is explicitly zeroed. Then > > again, do we really need it? If users are going to overwrite it anyway, > > do we even need to bother? I suppose it makes some sense because the > > current duty cycle is stale when the ->period gets set to the value from > > args. I think the documentation should mention this in some way. > > Yes, if we keep the current duty_cycle it can exceed the period value. > I'm fine dropping the ->duty_cycle = 0 assignment and documenting the > behavior. Actually what I was trying to suggest is that we keep the code as-is but document the behaviour (and rationale behind it). I think it's fine to zero out the value precisely because it could become invalid after the function (and there's no other reasonable value to set it to). Just wanted to make sure it's all properly documented. Thierry
diff --git a/include/linux/pwm.h b/include/linux/pwm.h index 17018f3..e09babf 100644 --- a/include/linux/pwm.h +++ b/include/linux/pwm.h @@ -148,6 +148,87 @@ static inline void pwm_get_args(const struct pwm_device *pwm, } /** + * pwm_prepare_new_state() - prepare a new state to be applied with + * pwm_apply_state() + * @pwm: PWM device + * @state: state to fill with the prepared PWM state + * + * This functions prepares a state that can later be tweaked and applied + * to the PWM device with pwm_apply_state(). This is a convenient function + * that first retrieves the current PWM state and the replaces the period + * and polarity fields with the reference values defined in pwm->args. + * Once the new state is created you can adjust the ->enable and ->duty_cycle + * according to your need before calling pwm_apply_state(). + */ +static inline void pwm_prepare_new_state(const struct pwm_device *pwm, + struct pwm_state *state) +{ + struct pwm_args args; + + /* First get the current state. */ + pwm_get_state(pwm, state); + + /* Then fill it with the reference config */ + pwm_get_args(pwm, &args); + + state->period = args.period; + state->polarity = args.polarity; + state->duty_cycle = 0; +} + +/** + * pwm_get_relative_duty_cycle() - Get a relative duty_cycle value + * @state: the PWM state to extract period and duty_cycle from + * @scale: the scale you want to use for you relative duty_cycle value + * + * This functions converts the absolute duty_cycle stored in @state + * (expressed in nanosecond) into a relative value. + * For example if you want to get the duty_cycle expressed in nanosecond, + * call: + * + * pwm_get_state(pwm, &state); + * duty = pwm_get_relative_duty_cycle(&state, 100); + */ +static inline unsigned int +pwm_get_relative_duty_cycle(const struct pwm_state *state, unsigned int scale) +{ + if (!state->period) + return 0; + + return DIV_ROUND_CLOSEST_ULL((u64)state->duty_cycle * scale, + state->period); +} + +/** + * pwm_set_relative_duty_cycle() - Set a relative duty_cycle value + * @state: the PWM state to fill + * @val: the relative duty_cycle value + * @scale: the scale you use for you relative duty_cycle value + * + * This functions converts a relative duty_cycle stored into an absolute + * one (expressed in nanoseconds), and put the result in state->duty_cycle. + * For example if you want to change configure a 50% duty_cycle, call: + * + * pwm_prepare_new_state(pwm, &state); + * pwm_set_relative_duty_cycle(&state, 50, 100); + * pwm_apply_state(pwm, &state); + */ +static inline void +pwm_set_relative_duty_cycle(struct pwm_state *state, unsigned int val, + unsigned int scale) +{ + if (!scale) + return; + + /* Make sure we don't have duty_cycle > period */ + if (val > scale) + val = scale; + + state->duty_cycle = DIV_ROUND_CLOSEST_ULL((u64)val * state->period, + scale); +} + +/** * struct pwm_ops - PWM controller operations * @request: optional hook for requesting a PWM * @free: optional hook for freeing a PWM
The pwm_prepare_new_state() helper prepares a new state object containing the current PWM state except for the polarity and period fields which are set to the reference values. This is particurly useful for PWM users who want to apply a new duty-cycle expressed relatively to the reference period without changing the enable state. The PWM framework expect PWM users to configure the duty cycle in nanosecond, but most users just want to express this duty cycle relatively to the period value (i.e. duty_cycle = 33% of the period). Add pwm_{get,set}_relative_duty_cycle() helpers to ease this kind of conversion. Signed-off-by: Boris Brezillon <boris.brezillon@free-electrons.com> --- include/linux/pwm.h | 81 +++++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 81 insertions(+)