[PATCH AUTOSEL 6.17-6.6] rtc: pcf2127: fix watchdog interrupt mask on pcf2131

[Sasha Levin <sashal@kernel.org>]

From: Bruno Thomsen <bruno.thomsen@gmail.com>

[ Upstream commit 87064da2db7be537a7da20a25c18ba912c4db9e1 ]

When using interrupt pin (INT A) as watchdog output all other
interrupt sources need to be disabled to avoid additional
resets. Resulting INT_A_MASK1 value is 55 (0x37).

Signed-off-by: Bruno Thomsen <bruno.thomsen@gmail.com>
Link: https://lore.kernel.org/r/20250902182235.6825-1-bruno.thomsen@gmail.com
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---

LLM Generated explanations, may be completely bogus:

YES — this change should go to stable.

- `drivers/rtc/rtc-pcf2127.c:611-623` now masks every INT A source
  except the watchdog bit on PCF2131 when `reset-source` is in use, so
  the INT A pin stays dedicated to driving the external reset pulse
  instead of reasserting on alarm/periodic/tamper events.
- Before this fix, `drivers/rtc/rtc-pcf2127.c:1174-1182` left all INT A
  mask bits cleared, and the probe path unconditionally enables several
  interrupt sources (see `pcf2127_enable_ts()` at `drivers/rtc/rtc-
  pcf2127.c:1128-1163`). With INT A wired as the watchdog output, any of
  those interrupts could immediately toggle the line and spuriously
  reset the system—effectively breaking boards that request
  watchdog/reset operation.
- The new masking runs only when CONFIG_WATCHDOG is enabled and the DT
  property requests watchdog output (`drivers/rtc/rtc-
  pcf2127.c:575-617`), so normal RTC users keep their interrupt
  functionality. If the write were to fail, behaviour simply falls back
  to the pre-fix state, so the delta carries minimal regression risk.
- The patch is tiny, self-contained to this driver, and fixes a user-
  visible bug (unwanted resets) without altering interfaces, making it
  an appropriate and low-risk stable backport candidate.

Suggested follow-up for maintainers: consider backporting anywhere
PCF2131 watchdog/reset support exists alongside unmasked INT A sources.

 drivers/rtc/rtc-pcf2127.c | 15 +++++++++++++++
 1 file changed, 15 insertions(+)

diff --git a/drivers/rtc/rtc-pcf2127.c b/drivers/rtc/rtc-pcf2127.c
index 3ba1de30e89c2..bb4fe81d3d62c 100644
--- a/drivers/rtc/rtc-pcf2127.c
+++ b/drivers/rtc/rtc-pcf2127.c
@@ -608,6 +608,21 @@ static int pcf2127_watchdog_init(struct device *dev, struct pcf2127 *pcf2127)
 			set_bit(WDOG_HW_RUNNING, &pcf2127->wdd.status);
 	}
 
+	/*
+	 * When using interrupt pin (INT A) as watchdog output, only allow
+	 * watchdog interrupt (PCF2131_BIT_INT_WD_CD) and disable (mask) all
+	 * other interrupts.
+	 */
+	if (pcf2127->cfg->type == PCF2131) {
+		ret = regmap_write(pcf2127->regmap,
+				   PCF2131_REG_INT_A_MASK1,
+				   PCF2131_BIT_INT_BLIE |
+				   PCF2131_BIT_INT_BIE |
+				   PCF2131_BIT_INT_AIE |
+				   PCF2131_BIT_INT_SI |
+				   PCF2131_BIT_INT_MI);
+	}
+
 	return devm_watchdog_register_device(dev, &pcf2127->wdd);
 }
 
-- 
2.51.0