Merge branch 'for-4.13/core' into for-next (d007a00b) · Commits · e / devices / android_kernel_oneplus_sm8150

Documentation/pwm.txt

+28 −18

Original line number	Diff line number	Diff line
		======================================
		Pulse Width Modulation (PWM) interface
		======================================

		This provides an overview about the Linux PWM interface

		@@ -16,7 +18,7 @@ Users of the legacy PWM API use unique IDs to refer to PWM devices.

		Instead of referring to a PWM device via its unique ID, board setup code
		should instead register a static mapping that can be used to match PWM
		consumers to providers, as given in the following example:
		consumers to providers, as given in the following example::

		static struct pwm_lookup board_pwm_lookup[] = {
		PWM_LOOKUP("tegra-pwm", 0, "pwm-backlight", NULL,
		@@ -40,7 +42,7 @@ New users should use the pwm_get() function and pass to it the consumer
		device or a consumer name. pwm_put() is used to free the PWM device. Managed
		variants of these functions, devm_pwm_get() and devm_pwm_put(), also exist.

		After being requested, a PWM has to be configured using:
		After being requested, a PWM has to be configured using::

		int pwm_apply_state(struct pwm_device pwm, struct pwm_state state);

		@@ -72,11 +74,14 @@ interface is provided to use the PWMs from userspace. It is exposed at
		pwmchipN, where N is the base of the PWM chip. Inside the directory you
		will find:

		npwm - The number of PWM channels this chip supports (read-only).
		npwm
		The number of PWM channels this chip supports (read-only).

		export - Exports a PWM channel for use with sysfs (write-only).
		export
		Exports a PWM channel for use with sysfs (write-only).

		unexport - Unexports a PWM channel from sysfs (write-only).
		unexport
		Unexports a PWM channel from sysfs (write-only).

		The PWM channels are numbered using a per-chip index from 0 to npwm-1.

		@@ -84,21 +89,26 @@ When a PWM channel is exported a pwmX directory will be created in the
		pwmchipN directory it is associated with, where X is the number of the
		channel that was exported. The following properties will then be available:

		period - The total period of the PWM signal (read/write).
		period
		The total period of the PWM signal (read/write).
		Value is in nanoseconds and is the sum of the active and inactive
		time of the PWM.

		duty_cycle - The active time of the PWM signal (read/write).
		duty_cycle
		The active time of the PWM signal (read/write).
		Value is in nanoseconds and must be less than the period.

		polarity - Changes the polarity of the PWM signal (read/write).
		polarity
		Changes the polarity of the PWM signal (read/write).
		Writes to this property only work if the PWM chip supports changing
		the polarity. The polarity can only be changed if the PWM is not
		enabled. Value is the string "normal" or "inversed".

		enable - Enable/disable the PWM signal (read/write).
		0 - disabled
		1 - enabled
		enable
		Enable/disable the PWM signal (read/write).

		- 0 - disabled
		- 1 - enabled

		Implementing a PWM driver
		-------------------------

drivers/pwm/core.c

+3 −1

Original line number	Diff line number	Diff line
		@@ -678,7 +678,9 @@ struct pwm_device of_pwm_get(struct device_node np, const char *con_id)

		pc = of_node_to_pwmchip(args.np);
		if (IS_ERR(pc)) {
		if (PTR_ERR(pc) != -EPROBE_DEFER)
		pr_err("%s(): PWM chip not found\n", __func__);

		pwm = ERR_CAST(pc);
		goto put;
		}