From mboxrd@z Thu Jan 1 00:00:00 1970 From: Boris Brezillon Date: Thu, 14 Apr 2016 19:17:42 +0000 Subject: [PATCH v5 22/24] pwm: update documentation Message-Id: <1460661464-11216-23-git-send-email-boris.brezillon@free-electrons.com> List-Id: References: <1460661464-11216-1-git-send-email-boris.brezillon@free-electrons.com> In-Reply-To: <1460661464-11216-1-git-send-email-boris.brezillon-wi1+55ScJUtKEb57/3fJTNBPR1lH4CV8@public.gmane.org> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: Thierry Reding , linux-pwm-u79uwXL29TY76Z2rM5mHXA@public.gmane.org Cc: Mike Turquette , Stephen Boyd , linux-clk-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, Mark Brown , Liam Girdwood , Kamil Debski , lm-sensors-GZX6beZjE8VD60Wz+7aTrA@public.gmane.org, Jean Delvare , Guenter Roeck , Dmitry Torokhov , linux-input-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, Bryan Wu , Richard Purdie , Jacek Anaszewski , linux-leds-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, Maxime Ripard , Chen-Yu Tsai , linux-sunxi-/JYPxA39Uh5TLH3MbocFFw@public.gmane.org, Joachim Eastwood , Thomas Petazzoni , Heiko Stuebner , linux-rockchip-IAPFreCvJWM7uuMidbF8XUB+6BGkLq7r@public.gmane.org, Jingoo Han , Lee Jones Update the PWM subsystem documentation to reflect the atomic PWM changes. Signed-off-by: Boris Brezillon --- Documentation/pwm.txt | 30 ++++++++++++++++++++++++++++-- 1 file changed, 28 insertions(+), 2 deletions(-) diff --git a/Documentation/pwm.txt b/Documentation/pwm.txt index ca895fd..789b27c 100644 --- a/Documentation/pwm.txt +++ b/Documentation/pwm.txt @@ -42,9 +42,26 @@ variants of these functions, devm_pwm_get() and devm_pwm_put(), also exist. After being requested, a PWM has to be configured using: -int pwm_config(struct pwm_device *pwm, int duty_ns, int period_ns); +int pwm_apply_state(struct pwm_device *pwm, struct pwm_state *state); -To start/stop toggling the PWM output use pwm_enable()/pwm_disable(). +This API controls both the PWM period/duty_cycle config and the +enable/disable state. + +The pwm_config(), pwm_enable() and pwm_disable() functions are just wrappers +around pwm_apply_state() and should not be used if the user wants to change +several parameter at once. For example, if you see pwm_config() and +pwm_{enable,disable}() calls in the same function, this probably means you +should switch to pwm_apply_state(). + +The PWM user API also allows one to query the PWM state with pwm_get_state(). + +In addition to the PWM state, the PWM API also exposes PWM arguments, which +are the reference PWM config one should use on this PWM. +PWM arguments are usually platform-specific and allows the PWM user to only +care about dutycycle relatively to the full period (like, duty = 50% of the +period). struct pwm_args contains 2 fields (period and polarity) and should +be used to set the initial PWM config (usually done in the probe function +of the PWM user). PWM arguments are retrieved with pwm_get_args(). Using PWMs with the sysfs interface ----------------------------------- @@ -105,6 +122,15 @@ goes low for the remainder of the period. Conversely, a signal with inversed polarity starts low for the duration of the duty cycle and goes high for the remainder of the period. +Drivers are encouraged to implement ->apply() instead of the legacy +->enable(), ->disable() and ->config() methods. Doing that should provide +atomicity in the PWM config workflow, which is required when the PWM controls +a critical device (like a regulator). + +The implementation of ->get_state() (a method used to retrieve initial PWM +state) is also encouraged for the same reason: letting the PWM user know +about the current PWM state would allow him to avoid glitches. + Locking ------- -- 2.5.0