[PATCH v4 0/4] rtc: Add NXP PCF8525 RTC driver with watchdog and hwmon

[Shiv Prakash Gupta]

The PCF8525 is an NXP I2C real-time clock using an external
32.768-kHz crystal. It provides alarms, external timestamp capture,
recording of the last calendar write, backup battery switch-over,
a hardware watchdog timer, and an on-chip temperature sensor.

This series introduces DT bindings, the core RTC driver, watchdog
support, and optional hardware-monitoring (temperature readout) via
the hwmon subsystem.

Changes in v4:
- Rework timestamp handling to serialize sysfs clear and IRQ
  processing, read Timestamp1 before clearing TSF, and restore TSM
  after the CTS command.
- Correct Timestamp2 handling to report the last calendar write
  instead of treating it as a second external timestamp capture.
- Rework the INTA threaded IRQ handler to drain pending AF/MSF/TSF
  events and re-read status registers, avoiding missed events on an
  edge-triggered IRQ.
- Preserve all CTRL2 Write-0-to-Clear status flags, including WDTF,
  across register read-modify-write operations.
- Rework watchdog support to use nINTB as the watchdog output without
  a Linux watchdog IRQ or pretimeout notification; remove unsupported
  pretimeout handling and write-only watchdog-value read.
- Establish a known watchdog state at probe, clear stale WDTF before
  enabling the watchdog output, and report the hardware-achieved
  timeout.
- Fix RTC feature and time-setting handling, including
  update-interrupt capability reporting and writing the
  hundredths-of-a-second register when setting the calendar.
- Improve interrupt/wakeup and device-managed cleanup ordering so
  hardware interrupt sources are safely masked on probe failure and
  driver removal.
- Rework hwmon registration and power-management handling so the
  temperature readout is enabled before exposure to userspace and
  cleanly disabled on failure, suspend, and removal.

Changes in v3:
- patch 2: protect the Write-0-to-Clear (W0C) status flags in the
  CTRL2/CTRL3 read-modify-write cycles so concurrently asserted
  interrupt events are not silently cleared
- patch 2: replace the timestamp spinlock with a mutex and re-read
  CTRL4 under it, closing the TOCTOU race between the threaded IRQ
  handler and the sysfs timestamp store
- patch 3: configure the nINTB/CLKOUT pin (CLKOE=0) before requesting
  the watchdog IRQ to avoid a spurious interrupt storm
- patch 3: add suspend/resume PM ops to stop and re-ping the watchdog
  across system sleep
- patch 3: add WDIOF_PRETIMEOUT so the watchdog core attaches a
  pretimeout governor
- patch 3: re-mask INTA/INTB interrupts on driver unbind via devm
  cleanup actions
- patch 4: enable TEMP_RD_EN before registering the hwmon device and
  add a devm cleanup to disable it on unbind

Changes in v2:
- Fix include: use <linux/pm_wakeirq.h> instead of <pm_wakeup.h>
- Add spinlock_t ts_lock to protect ts[]/ts_valid[] from IRQ/sysfs race
- Fix W0C ordering: clear AF/TSF flags before acting on alarm/timestamp
  events
- Use dev_pm_set_wake_irq() for suspend wakeup wiring
- Clear stale WDTF before unmasking watchdog interrupt on INTB to prevent
  boot loop when battery-backed flag persists across resets
- Add watchdog_notify_pretimeout() call in INTB IRQ handler
- Set WDOG_HW_RUNNING if bootloader left watchdog running at probe time
- Register hwmon device first, then enable PCF8525_CTRL5_TEMP_RD_EN only
  after successful registration

Shiv Prakash Gupta (4):
  dt-bindings: rtc: Add NXP PCF8525 RTC
  rtc: pcf8525: Add NXP PCF8525 RTC driver
  rtc: pcf8525: Add watchdog support
  rtc: pcf8525: Add temperature sensor support via hwmon

 .../devicetree/bindings/rtc/nxp,pcf8525.yaml  |   86 +
 MAINTAINERS                                   |    7 +
 drivers/rtc/Kconfig                           |   25 +
 drivers/rtc/Makefile                          |    1 +
 drivers/rtc/rtc-pcf8525.c                     | 1608 +++++++++++++++++
 5 files changed, 1727 insertions(+)
 create mode 100644 Documentation/devicetree/bindings/rtc/nxp,pcf8525.yaml
 create mode 100644 drivers/rtc/rtc-pcf8525.c

-- 
2.34.1