On Wed, Mar 21, 2018 at 10:10:36AM +0530, Rajkumar Rampelli wrote:
> Add support for pwm HW driver which has only capture functionality.
> This helps to implement the PWM based Tachometer driver which reads
> the PWM output signals from electronic fans.
>
> PWM Tachometer captures the period and duty cycle of the PWM signal
>
> Add conditional checks for callabacks enable(), disable(), config()
> to check if they are supported by the client driver or not. Skip these
> callbacks if they are not supported.
>
> Signed-off-by: Rajkumar Rampelli <rrajk@xxxxxxxxxx>
> ---
>
> V2: Added if conditional checks for pwm callbacks since drivers may
> implements only pwm capture functionality.
>
> drivers/pwm/core.c | 21 +++++++++++++++------
> 1 file changed, 15 insertions(+), 6 deletions(-)
>
> diff --git a/drivers/pwm/core.c b/drivers/pwm/core.c
> index 1581f6a..f70fe68 100644
> --- a/drivers/pwm/core.c
> +++ b/drivers/pwm/core.c
> @@ -246,6 +246,10 @@ static bool pwm_ops_check(const struct pwm_ops *ops)
> if (ops->apply)
> return true;
>
> + /* driver supports capture operation */
> + if (ops->capture)
> + return true;
> +
> return false;
> }
>
> @@ -495,7 +499,8 @@ int pwm_apply_state(struct pwm_device *pwm, struct pwm_state *state)
> * ->apply().
> */
> if (pwm->state.enabled) {
> - pwm->chip->ops->disable(pwm->chip, pwm);
> + if (pwm->chip->ops->disable)
> + pwm->chip->ops->disable(pwm->chip, pwm);
This is not a good idea. It means that you'll be able to successfully
configure a capture-only PWM channel for output. I think all of the
output configuration functions should return an error (-ENOSYS?) for
capture-only devices, much like we return -ENOSYS for pwm_capture() if
the driver doesn't implement capture support.
Thierry
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