Messages in this thread Patch in this message | | | Date | Tue, 12 Apr 2016 12:08:45 +0200 | From | Thierry Reding <> | Subject | Re: [RESEND 01/11] pwm: Add PWM Capture support |
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On Wed, Mar 02, 2016 at 03:31:59PM +0000, Lee Jones wrote: > Supply a PWM Capture call-back Op in order to pass back > information obtained by running analysis on PWM a signal. > This would normally (at least during testing) be called from > the Sysfs routines with a view to printing out PWM Capture > data which has been encoded into a string. > > Signed-off-by: Lee Jones <lee.jones@linaro.org> > --- > drivers/pwm/core.c | 26 ++++++++++++++++++++++++++ > include/linux/pwm.h | 13 +++++++++++++ > 2 files changed, 39 insertions(+)
Overall I like the concept of introducing this capture functionality.
However I have a couple of questions, see below.
> diff --git a/drivers/pwm/core.c b/drivers/pwm/core.c > index d24ca5f..8f4a8a9 100644 > --- a/drivers/pwm/core.c > +++ b/drivers/pwm/core.c > @@ -494,6 +494,32 @@ unlock: > EXPORT_SYMBOL_GPL(pwm_set_polarity); > > /** > + * pwm_capture() - capture and report a PWM signal > + * @pwm: PWM device > + * @channel: PWM capture channel to use > + * @buf: buffer to place output message into > + * > + * Returns: 0 on success or a negative error code on failure. > + */ > +int pwm_capture(struct pwm_device *pwm, int channel, char *buf)
This public interface seems to be targetted specifically at sysfs. As such I'm not sure if there is reason to make it public, since the code is unlikely to ever be called by other users in the kernel.
Do you think it would be possible to make the interface more generic by passing back some form of structure containing the capture result? That way users within the kernel could use the result without having to go and parse a string filled in by the driver. It would also be easy to implement sysfs support on top of that. Another advantage is that there would be a standard result structure rather than a free-form string filled by drivers that can't be controlled.
What kind of result does the STi hardware return? Looking at the driver later in the series it seems to support triggering interrupts on rising and falling edges and capture some running counter at these events. If the frequency of the counter increment is known, these numbers should allow us to determine both the period and duty cycle of the PWM signal in nanoseconds. Would it be possible to rewrite this function and the driver patch to something like this:
int pwm_capture(struct pwm_device *pwm, struct pwm_capture *result);
Where
struct pwm_capture { unsigned int period; unsigned int duty_cycle; }; ?
Another thing I noticed is that the code here seems to be confusing channels and devices. In the PWM subsystem a struct pwm_device represents a single channel. Allowing the channel to be specified is redundant at best, and confusing at worst.
Thierry [unhandled content-type:application/pgp-signature] | |