add NXP RTC driver support for S32G2/S32G3 SoCs

From: Ciprian Marian Costea <ciprianmarian.costea@oss.nxp.com>

This patch series add support for the NXP RTC hardware module present on
S32G2/S32G3 SoCs.

RTC tracks clock time during system suspend. It is used as a time-based
wakeup source for the S32G2/S32G3 SoCs.

RTC is not battery-powered and it is not kept alive during system reset.

Following is an example of Suspend to RAM trigger on S32G2/S32G3 SoCs,
using userspace tools such as rtcwake:
# rtcwake -s 2 -m mem
# rtcwake: assuming RTC uses UTC ...
# rtcwake: wakeup from "mem" using /dev/rtc0 at Wed Feb  6 06:28:36 2036
#

Changes in V6:
- Fixed a coding style issue regarding kernel doc reported by kernel test robot
- Refactored small sections from the S32G RTC driver without impacting
  functionality
- Fixed an error probe path issue on S32G RTC driver.
- Added 'rtc' schema in S32G-RTC bindings

Changes in V5:
- Removed rollover support.
- Removed clock switching support between Runtime and Suspend. A clock source
  which is always available has been used instead.
- Enabled 512 value RTC hardware frequency divisor to achieve higher rollover
  time
- Removed unneeded 'remove' callback.
- Decreased driver print verbosity on error paths.
- Provided 'clock-names' actual names in bindings documentation
- Remove __maybe_unused notations. Used the DEFINE_SIMPLE_DEV_PM_OPS() and
  pm_sleep_ptr() macros to handle the .suspend/.resume callbacks.
- Fixed some alignment issues.

Changes in V4:
- Dropped 'assigned-*' clock management approach. Simplified RTC Runtime
  and Suspend/Standby clock configuration.
- Simplified error paths on probe function
- Removed node label from bindings example
- Several cosmetic coding style fixes

Changes in V3:
- Removed 'nxp,s32g3-rtc' compatible string
- Change to 'remove' callback from 'remove_new'
- Used 'dev.parent' from 'struct rtc_device' instead of defining a
  specific 'struct device' in driver data
- Fixed several errors reported by kernel test robot
- Removed 'assigned-clocks', 'assigned-clock-parents' and
  'assigned-clock-rates' from required properties in the binding
  documentation.
- Refactored S32G RTC driver such that a default clock source and
  divisors configuration will be applied in case 'assigned-clocks' and
  'assigned-clock-parents' properties are missing.

Changes in V2:
- Removed 'clksel' support from dts bindings. Used clock parents support
  from CCF to better illustrate the RTC hardware IP from S32G2/S32G3.
- Removed frequency dividers support from dts bindings. Used assigned
  clock frequencies support from CCF instead.
- Reduced the interval while RTC is voluntarily disabled to a simple
  register write in order to avoid any race condition between a possbile
  rollover and 'suspend' callback execution flow.
- Updated bindings documentation with respect to clocking support.
- Fixed a potential unused variable warning reported by kernel test robot.
- Updated to usage of 'devm_rtc_allocate_device' and 'devm_rtc_register_device'
  instead of deprecated 'devm_rtc_device_register'.

Ciprian Marian Costea (4):
  dt-bindings: rtc: add schema for NXP S32G2/S32G3 SoCs
  rtc: s32g: add NXP S32G2/S32G3 SoC support
  arm64: defconfig: add S32G RTC module support
  MAINTAINERS: add NXP S32G RTC driver

 .../devicetree/bindings/rtc/nxp,s32g-rtc.yaml |  72 +++
 MAINTAINERS                                   |   2 +
 arch/arm64/configs/defconfig                  |   1 +
 drivers/rtc/Kconfig                           |  11 +
 drivers/rtc/Makefile                          |   1 +
 drivers/rtc/rtc-s32g.c                        | 529 ++++++++++++++++++
 6 files changed, 616 insertions(+)
 create mode 100644 Documentation/devicetree/bindings/rtc/nxp,s32g-rtc.yaml
 create mode 100644 drivers/rtc/rtc-s32g.c

-- 
2.45.2