[PATCH v4 0/2] Raspberry Pi 5 RTC driver

[Sander Speetjens]

The Raspberry Pi 5 has a battery-backed RTC located
on the DA9091 PMIC accessed via the I2C bus[1].
Access to the RTC is provided exclusively through the VideoCore firmware
mailbox interface (not via a direct I2C register interface).

As stated by jamesh on the Rasperry Pi forum [2],
"There are no plans to release a public datasheet for the DA9091."
So we are stuck with the firmware interface for now.
PhilE also states that "The firmware needs full control of the DA9091,
sometimes with extremely low latency,
otherwise there's a risk the supply could just cut the power."

This series adds:
  - a DT property for the charging voltage of the RTC battery
  - the RTC driver that talks to the firmware

The driver and binding are based on (and largely taken from) the
downstream Raspberry Pi kernel. The main changes for upstream are
the addition of a dt binding property for setting the charging voltage and
binding the driver from the raspberrypi-firmware driver instead of from
the DT.

The driver supports time read/write, alarm, and optional trickle
charging voltage configuration via the device-tree.

Testing
- Hardware: Raspberry Pi 5 Model B revC
- Kernel: v7.2
- dt_binding_check: passed
- Basic RTC operations (read/write time, alarm) verified

[1] https://www.raspberrypi.com/news/introducing-raspberry-pi-5/
[2] https://forums.raspberrypi.com/viewtopic.php?t=359073

Sander Speetjens (2):
  dt-bindings: rtc: Add property for Raspberry Pi 5 RTC
  rtc: Add Raspberry Pi 5 RTC driver

 .../arm/bcm/raspberrypi,bcm2835-firmware.yaml |   8 +
 drivers/firmware/raspberrypi.c                |  25 ++
 drivers/rtc/Kconfig                           |  12 +
 drivers/rtc/Makefile                          |   1 +
 drivers/rtc/rtc-raspberrypi.c                 | 242 ++++++++++++++++++
 5 files changed, 288 insertions(+)
 create mode 100644 drivers/rtc/rtc-raspberrypi.c


base-commit: 93f51579e7df248780214094418f205253383cc5
-- 
2.55.0