rtc: microchip: Add driver for PolarFire SoC

Hey all,
This is technically a v4 of [0], although a fair bit of time has
passed since then. In the meantime I upstreamed the dt-binding, which
was in the v1, and this patch depends on the fixes to the dt-binding
and device tree etc which landed in v5.18-rc5.

The driver is quite substantially rewritten from the v1, as you wanted
it to be switched to "binary" rather than calendar mode - so hopefully I
have satisfied your concerns with the original driver. Specifically you
had an significant issue with the counter being reset on startup & that
is no longer the case.

Thanks,
Conor.

Changes since v3:
- invert read order of datetime registers so that they are properly
  aligned. reads of the upper register are aligned to the last read
  of the lower register
- move wakeup_irq out of mpfs_rtc_dev & into probe
- removed range_min since it is not set & implicity zero anyway
- rewrote the remove function to not call mpfs_rtc_alarm_irq_enable(,0)

Changes from v2:
- move prescaler out of mpfs_rtc_dev & into probe

Changes from v1:
- remove duplicate and unused defines
- remove oneline mpfs_rtc_set_prescaler function
- dont unconditionally turn off the rtc in the init function
- dont reset the rtc when init is run.
- dont disable the alarm when we boot
- use binary, not calendar mode
- delete mpfs_rtc_init & set prescale in probe
- use dev_pm_set_wake_irq rather than writing suspend/resume functions
- delete calendar mode only register defines
- since using binary mode, set range min to zero
- set range max to max alarm value (is this acceptable?)
- added a MAINTAINERS entry: when v1 was submitted there was nothing to
  add to, but there is now.

[0] https://lore.kernel.org/linux-rtc/20210512111133.1650740-...

Conor Dooley (2):
  rtc: Add driver for Microchip PolarFire SoC
  MAINTAINERS: add PolarFire SoC's RTC

 MAINTAINERS            |   1 +
 drivers/rtc/Kconfig    |  10 ++
 drivers/rtc/Makefile   |   1 +
 drivers/rtc/rtc-mpfs.c | 326 +++++++++++++++++++++++++++++++++++++++++
 4 files changed, 338 insertions(+)
 create mode 100644 drivers/rtc/rtc-mpfs.c


base-commit: c5eb0a61238dd6faf37f58c9ce61c9980aaffd7a
-- 
2.36.1