[PATCH v2 0/2] rtc: add a driver for the Freescale MCF5441x on-chip RTC

This series adds support for the "robust" real time clock found on the
Freescale MCF5441x family of ColdFire SoCs.

Patch 1 adds the rtc-class driver. Besides the usual time/calendar and a
one-shot alarm, the block contains 2KB of battery-backed standby RAM that
survives a main-power loss while VSTBY_RTC is supplied; the driver exposes
it through the nvmem framework so userspace can persist data (for example a
reset/reboot counter) across power cycles. Register and standby-RAM writes
go through the RTC_CR[WE] knock sequence, the time counters are read under
the RTC_SR[INVAL] guard described in the reference manual, and the time/date
encoding is forced to binary at probe.

Patch 2 registers the platform device from the m5441x ColdFire SoC support
code so that every MCF5441x board gets the RTC. The MCFRTC_BASE, MCFRTC_SIZE
and MCF_IRQ_RTC definitions it relies on already exist in
arch/m68k/include/asm/m5441xsim.h.

The driver has been exercised on an MCF54418-based board: it registers
as an rtc device, exposes the standby RAM as an nvmem device, and a value
written to the standby RAM survives a mains power-cycle.

Signed-off-by: Jean-Michel Hautbois <[email protected]>
---
Changes in v2:
- Patch 1: wait_valid() now uses read_poll_timeout_atomic() instead of an
  open-coded busy-wait. The atomic variant is required because it runs with
  p->lock held and interrupts off. (Geert Uytterhoeven)
- Patch 1: nvram_read()/nvram_write() use unsigned int rather than size_t
  for the chunk/index locals, and scoped_guard(spinlock_irqsave) instead of
  explicit spin_lock_irqsave()/spin_unlock_irqrestore(). (Geert Uytterhoeven)
- Link to v1: https://patch.msgid.link/[email protected]

---
Jean-Michel Hautbois (2):
      rtc: m5441x: add MCF5441x on-chip RTC driver
      m68k: coldfire/m5441x: register the on-chip RTC

 MAINTAINERS                 |   6 +
 arch/m68k/coldfire/m5441x.c |  29 +++
 drivers/rtc/Kconfig         |  12 +
 drivers/rtc/Makefile        |   1 +
 drivers/rtc/rtc-m5441x.c    | 579 ++++++++++++++++++++++++++++++++++++++++++++
 5 files changed, 627 insertions(+)
---
base-commit: 979c294509f9248fe1e7c358d582fb37dd5ca12d
change-id: 20260529-jmh-upstream-coldfire-rtc-88b095b2cf28

Best regards,
--  
Jean-Michel Hautbois <[email protected]>