rtc: add stand-alone driver for RX8025 chip

Add support for the Epson RX-8025SA/NB RTC chips.  It includes support for
alarms, periodic interrupts (1 Hz) and clock precision adjustment.

For clock precision adjustment, the SYSFS file "clock_adjust_ppb" gets
created in "/sys/class/rtc/rtcX/device".  It permits to set and get the
clock adjustment in ppb (parts per billion), e.g.:

  # echo -183000 > /sys/class/rtc/rtc0/device/clock_adjust_ppb
  # cat /sys/class/rtc/rtc0/device/clock_adjust_ppb
  -183000

This allows to compensate temperature dependent clock drifts.  According
to the RX8025 SA/NB application manual the frequency and temperature
characteristics can be approximated using the following equation:

  df = a * (ut - t)**2

  df: Frequency deviation in any temperature
  a : Coefficient = (-35 +-5) * 10**-9
  ut: Ultimate temperature in degree = +25 +-5 degree
  t : Any temperature in degree

Signed-off-by: Wolfgang Grandegger <[email protected]>
Signed-off-by: Sergei Poselenov <[email protected]>
Signed-off-by: Yuri Tikhonov <[email protected]>
Signed-off-by: Dmitry Rakhchev <[email protected]>
Signed-off-by: Matthias Fuchs <[email protected]>
Acked-by: Jean Delvare <[email protected]>
Signed-off-by: Alessandro Zummo <[email protected]>
Cc: David Brownell <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

0 files changed, 0 insertions, 0 deletions