Lines Matching +full:- +full:pwm
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.
15 ----------------
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
24 PWM_LOOKUP("tegra-pwm", 0, "pwm-backlight", NULL,
36 ----------
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::
44 int pwm_apply_might_sleep(struct pwm_device *pwm, struct pwm_state *state);
46 This API controls both the PWM period/duty_cycle config and the
49 PWM devices can be used from atomic context, if the PWM does not sleep. You
52 bool pwm_might_sleep(struct pwm_device *pwm);
54 If false, the PWM can also be configured from atomic context with::
56 int pwm_apply_atomic(struct pwm_device *pwm, struct pwm_state *state);
58 As a consumer, don't rely on the output's state for a disabled PWM. If it's
63 There is also a usage_power setting: If set, the PWM driver is only required to
74 The PWM user API also allows one to query the PWM state that was passed to the
80 In addition to the PWM state, the PWM API also exposes PWM arguments, which
81 are the reference PWM config one should use on this PWM.
82 PWM arguments are usually platform-specific and allows the PWM user to only
85 be used to set the initial PWM config (usually done in the probe function
86 of the PWM user). PWM arguments are retrieved with pwm_get_args().
88 All consumers should really be reconfiguring the PWM upon resume as
93 -----------------------------------
97 /sys/class/pwm/. Each probed PWM controller/chip will be exported as
98 pwmchipN, where N is the base of the PWM chip. Inside the directory you
102 The number of PWM channels this chip supports (read-only).
105 Exports a PWM channel for use with sysfs (write-only).
108 Unexports a PWM channel from sysfs (write-only).
110 The PWM channels are numbered using a per-chip index from 0 to npwm-1.
112 When a PWM channel is exported a pwmX directory will be created in the
117 The total period of the PWM signal (read/write).
119 time of the PWM.
122 The active time of the PWM signal (read/write).
126 Changes the polarity of the PWM signal (read/write).
127 Writes to this property only work if the PWM chip supports changing
132 Enable/disable the PWM signal (read/write).
134 - 0 - disabled
135 - 1 - enabled
137 Implementing a PWM driver
138 -------------------------
140 Currently there are two ways to implement pwm drivers. Traditionally
143 to have multiple PWM drivers in the system. For this reason it's mandatory
144 for new drivers to use the generic PWM framework.
146 A new PWM controller/chip can be allocated using pwmchip_alloc(), then
149 pwm_chip as argument which provides a description of the PWM chip, the number
150 of PWM devices provided by the chip and the chip-specific implementation of the
151 supported PWM operations to the framework.
153 When implementing polarity support in a PWM driver, make sure to respect the
154 signal conventions in the PWM framework. By definition, normal polarity
160 Drivers are encouraged to implement ->apply() instead of the legacy
161 ->enable(), ->disable() and ->config() methods. Doing that should provide
162 atomicity in the PWM config workflow, which is required when the PWM controls
165 The implementation of ->get_state() (a method used to retrieve initial PWM
166 state) is also encouraged for the same reason: letting the PWM user know
167 about the current PWM state would allow him to avoid glitches.
173 -------
175 The PWM core list manipulations are protected by a mutex, so pwm_get()
177 PWM core does not enforce any locking to pwm_enable(), pwm_disable() and
182 -------
184 Currently a PWM can only be configured with period_ns and duty_ns. For several