Documentation/driver-api/pwm.rst

2 Pulse Width Modulation (PWM) interface
5 This provides an overview about the Linux PWM interface
9 the Linux PWM API (although they could). However, PWMs are often
12 this kind of flexibility the generic PWM API exists.
17 Users of the legacy PWM API use unique IDs to refer to PWM devices.
19 Instead of referring to a PWM device via its unique ID, board setup code
20 should instead register a static mapping that can be used to match PWM
39 consumer name. pwm_put() is used to free the PWM device. Managed variants of
42 After being requested, a PWM has to be configured using::
46 This API controls both the PWM period/duty_cycle config and the
49 As a consumer, don't rely on the output's state for a disabled PWM. If it's
54 There is also a usage_power setting: If set, the PWM driver is only required to
65 The PWM user API also allows one to query the PWM state that was passed to the
71 In addition to the PWM state, the PWM API also exposes PWM arguments, which
72 are the reference PWM config one should use on this PWM.
73 PWM arguments are usually platform-specific and allows the PWM user to only
76 be used to set the initial PWM config (usually done in the probe function
77 of the PWM user). PWM arguments are retrieved with pwm_get_args().
79 All consumers should really be reconfiguring the PWM upon resume as
88 /sys/class/pwm/. Each probed PWM controller/chip will be exported as
89 pwmchipN, where N is the base of the PWM chip. Inside the directory you
93     The number of PWM channels this chip supports (read-only).
96     Exports a PWM channel for use with sysfs (write-only).
99    Unexports a PWM channel from sysfs (write-only).
101 The PWM channels are numbered using a per-chip index from 0 to npwm-1.
103 When a PWM channel is exported a pwmX directory will be created in the
108     The total period of the PWM signal (read/write).
110     time of the PWM.
113     The active time of the PWM signal (read/write).
117     Changes the polarity of the PWM signal (read/write).
118     Writes to this property only work if the PWM chip supports changing
119     the polarity. The polarity can only be changed if the PWM is not
123     Enable/disable the PWM signal (read/write).
128 Implementing a PWM driver
134 to have multiple PWM drivers in the system. For this reason it's mandatory
135 for new drivers to use the generic PWM framework.
137 A new PWM controller/chip can be added using pwmchip_add() and removed
139 pwm_chip as argument which provides a description of the PWM chip, the
140 number of PWM devices provided by the chip and the chip-specific
141 implementation of the supported PWM operations to the framework.
143 When implementing polarity support in a PWM driver, make sure to respect the
144 signal conventions in the PWM framework. By definition, normal polarity
152 atomicity in the PWM config workflow, which is required when the PWM controls
155 The implementation of ->get_state() (a method used to retrieve initial PWM
156 state) is also encouraged for the same reason: letting the PWM user know
157 about the current PWM state would allow him to avoid glitches.
165 The PWM core list manipulations are protected by a mutex, so pwm_get()
167 PWM core does not enforce any locking to pwm_enable(), pwm_disable() and
174 Currently a PWM can only be configured with period_ns and duty_ns. For several