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kernel
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linux
pwm: Standardize document format
Each text file under Documentation follows a different format. Some
don't even have titles!
Change its representation to follow the adopted standard, using ReST
markup for it to be parseable by Sphinx:
- mark document title;
- mark literal blocks;
- better format the parameters.
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>
Signed-off-by: Thierry Reding <thierry.reding@gmail.com>
authored by
Mauro Carvalho Chehab
and committed by
Thierry Reding
c571123c
2ea659a9
+28
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+28
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Documentation/pwm.txt
+28
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Documentation/pwm.txt
···
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======================================
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Pulse Width Modulation (PWM) interface
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======================================
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This provides an overview about the Linux PWM interface
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···
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Instead of referring to a PWM device via its unique ID, board setup code
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should instead register a static mapping that can be used to match PWM
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consumers to providers, as given in the following example:
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consumers to providers, as given in the following example::
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static struct pwm_lookup board_pwm_lookup[] = {
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PWM_LOOKUP("tegra-pwm", 0, "pwm-backlight", NULL,
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device or a consumer name. pwm_put() is used to free the PWM device. Managed
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variants of these functions, devm_pwm_get() and devm_pwm_put(), also exist.
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After being requested, a PWM has to be configured using:
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After being requested, a PWM has to be configured using::
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int pwm_apply_state(struct pwm_device *pwm, struct pwm_state *state);
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int pwm_apply_state(struct pwm_device *pwm, struct pwm_state *state);
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This API controls both the PWM period/duty_cycle config and the
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enable/disable state.
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pwmchipN, where N is the base of the PWM chip. Inside the directory you
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will find:
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npwm - The number of PWM channels this chip supports (read-only).
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npwm
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The number of PWM channels this chip supports (read-only).
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export - Exports a PWM channel for use with sysfs (write-only).
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export
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Exports a PWM channel for use with sysfs (write-only).
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unexport - Unexports a PWM channel from sysfs (write-only).
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unexport
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Unexports a PWM channel from sysfs (write-only).
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The PWM channels are numbered using a per-chip index from 0 to npwm-1.
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···
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pwmchipN directory it is associated with, where X is the number of the
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channel that was exported. The following properties will then be available:
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period - The total period of the PWM signal (read/write).
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Value is in nanoseconds and is the sum of the active and inactive
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time of the PWM.
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period
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The total period of the PWM signal (read/write).
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Value is in nanoseconds and is the sum of the active and inactive
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time of the PWM.
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duty_cycle - The active time of the PWM signal (read/write).
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Value is in nanoseconds and must be less than the period.
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duty_cycle
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The active time of the PWM signal (read/write).
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Value is in nanoseconds and must be less than the period.
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polarity - Changes the polarity of the PWM signal (read/write).
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Writes to this property only work if the PWM chip supports changing
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the polarity. The polarity can only be changed if the PWM is not
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enabled. Value is the string "normal" or "inversed".
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polarity
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Changes the polarity of the PWM signal (read/write).
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Writes to this property only work if the PWM chip supports changing
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the polarity. The polarity can only be changed if the PWM is not
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enabled. Value is the string "normal" or "inversed".
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enable - Enable/disable the PWM signal (read/write).
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0 - disabled
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1 - enabled
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enable
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Enable/disable the PWM signal (read/write).
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- 0 - disabled
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- 1 - enabled
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Implementing a PWM driver
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-------------------------