What:  /sys/class/pwm/
Date:  May 2013
KernelVersion: 3.11
Contact: H Hartley Sweeten <hsweeten@visionengravers.com>
Description:
  The pwm/ class sub-directory belongs to the Generic PWM
  Framework and provides a sysfs interface for using PWM
  channels.

What:  /sys/class/pwm/pwmchip<N>/
Date:  May 2013
KernelVersion: 3.11
Contact: H Hartley Sweeten <hsweeten@visionengravers.com>
Description:
  A /sys/class/pwm/pwmchipN directory is created for each
  probed PWM controller/chip where N is the base of the
  PWM chip.

What:  /sys/class/pwm/pwmchip<N>/npwm
Date:  May 2013
KernelVersion: 3.11
Contact: H Hartley Sweeten <hsweeten@visionengravers.com>
Description:
  The number of PWM channels supported by the PWM chip.

What:  /sys/class/pwm/pwmchip<N>/export
Date:  May 2013
KernelVersion: 3.11
Contact: H Hartley Sweeten <hsweeten@visionengravers.com>
Description:
  Exports a PWM channel from the PWM chip for sysfs control.
  Value is between 0 and /sys/class/pwm/pwmchipN/npwm - 1.

What:  /sys/class/pwm/pwmchip<N>/unexport
Date:  May 2013
KernelVersion: 3.11
Contact: H Hartley Sweeten <hsweeten@visionengravers.com>
Description:
  Unexports a PWM channel.

What:  /sys/class/pwm/pwmchip<N>/pwmX
Date:  May 2013
KernelVersion: 3.11
Contact: H Hartley Sweeten <hsweeten@visionengravers.com>
Description:
  A /sys/class/pwm/pwmchipN/pwmX directory is created for
  each exported PWM channel where X is the exported PWM
  channel number.

What:  /sys/class/pwm/pwmchip<N>/pwmX/period
Date:  May 2013
KernelVersion: 3.11
Contact: H Hartley Sweeten <hsweeten@visionengravers.com>
Description:
  Sets the PWM signal period in nanoseconds.

What:  /sys/class/pwm/pwmchip<N>/pwmX/duty_cycle
Date:  May 2013
KernelVersion: 3.11
Contact: H Hartley Sweeten <hsweeten@visionengravers.com>
Description:
  Sets the PWM signal duty cycle in nanoseconds.

What:  /sys/class/pwm/pwmchip<N>/pwmX/polarity
Date:  May 2013
KernelVersion: 3.11
Contact: H Hartley Sweeten <hsweeten@visionengravers.com>
Description:
  Sets the output polarity of the PWM signal to "normal" or
  "inversed".

What:  /sys/class/pwm/pwmchip<N>/pwmX/enable
Date:  May 2013
KernelVersion: 3.11
Contact: H Hartley Sweeten <hsweeten@visionengravers.com>
Description:
  Enable/disable the PWM signal.
  0 is disabled
  1 is enabled

What:  /sys/class/pwm/pwmchip<N>/pwmX/capture
Date:  June 2016
KernelVersion: 4.8
Contact: Lee Jones <lee@kernel.org>
Description:
  Capture information about a PWM signal. The output format is a
  pair unsigned integers (period and duty cycle), separated by a
  single space.