What:		/sys/class/pwm/
Date:		March 2013
KernelVersion:	3.11
Contact:	Lars Poeschel <poeschel@lemonage.de>
Description:

  The sysfs interface for PWM is selectable as a Kconfig option.
  If a driver successfully probed a pwm chip, it appears at
  /sys/class/pwm/pwmchipN/ where N is the number of it's first PWM channel. A
  single driver may probe multiple chips. PWMs are identified as they are
  inside the kernel, using integers in the range 0..MAX_PWMS. To use an
  individual PWM, you have to explicitly export it by writing it's kernel
  global number into the /sys/class/pwm/export file. Write it's number to
  /sys/class/pwm/unexport to make the pwm available for other uses.
  After a PWM channel is exported, it is available under
  /sys/class/pwm/pwmN/. Under this directory you can set the parameters for
  this PWM channel and at least let it start running.
  See below for the parameters.
  It is recommended to set the period_ns at first and the duty_ns after that.

  See Documentation/pwm.txt for more information.

Directory structure:

	/sys/class/pwm
		/export ... asks the kernel to export a PWM to userspace
		/unexport ... to return a PWM to the kernel
		/pwmN ... for each exported PWM #N
			/duty_ns ... r/w, length of duty portion
			/period_ns ... r/w, length of the pwm period
			/polarity ... r/w, normal(0) or inverse(1) polarity
					only created if driver supports it
			/run ... r/w, write 1 to start and 0 to stop the pwm
		/pwmchipN ... for each pwmchip; #N is its first PWM
			/base ... (r/o) same as N
			/ngpio ... (r/o) number of PWM; numbered N .. MAX_PWMS

