linux-kernel - [PATCH] rtc: pcf2127: clear minute/second interrupt

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Message-Id: <20250825-rtc-irq-v1-1-0133319406a7@solid-run.com>
Date: Mon, 25 Aug 2025 19:54:09 +0200
From: Josua Mayer <josua@...id-run.com>
To: Alexandre Belloni <alexandre.belloni@...tlin.com>
Cc: linux-rtc@...r.kernel.org, linux-kernel@...r.kernel.org,
 Josua Mayer <josua@...id-run.com>
Subject: [PATCH] rtc: pcf2127: clear minute/second interrupt

PCF2127 can generate interrupt every full second or minute configured
from control and status register 1, bits MI (1) and SI (0).

On interrupt control register 2 bit MSF (7) is set and must be cleared
to continue normal operation.

While the driver never enables this interrupt on its own, users or
firmware may do so - e.g. as an easy way to test the interrupt.

Add preprocessor definition for MSF bit and include it in the irq
bitmask to ensure minute and second interrupts are cleared when fired.

This fixes an issue where the rtc enters a test mode and becomes
unresponsive after a second interrupt has fired and is not cleared in
time. In this state register writes to control registers have no
effect and the interrupt line is kept asserted [1]:

[1] userspace commands to put rtc into unresponsive state:
$ i2cget -f -y 2 0x51 0x00
0x04
$ i2cset -f -y 2 0x51 0x00 0x05 # set bit 0 SI
$ i2cget -f -y 2 0x51 0x00
0x84 # bit 8 EXT_TEST set
$ i2cset -f -y 2 0x51 0x00 0x05 # try overwrite control register
$ i2cget -f -y 2 0x51 0x00
0x84 # no change

Signed-off-by: Josua Mayer <josua@...id-run.com>
---
 drivers/rtc/rtc-pcf2127.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/drivers/rtc/rtc-pcf2127.c b/drivers/rtc/rtc-pcf2127.c
index 2e1ac0c42e9323dbc6793840a265e8a663e52568..3ba1de30e89c22ae07ea319d530b58adc25b520d 100644
--- a/drivers/rtc/rtc-pcf2127.c
+++ b/drivers/rtc/rtc-pcf2127.c
@@ -42,6 +42,7 @@
 #define PCF2127_BIT_CTRL2_AF			BIT(4)
 #define PCF2127_BIT_CTRL2_TSF2			BIT(5)
 #define PCF2127_BIT_CTRL2_WDTF			BIT(6)
+#define PCF2127_BIT_CTRL2_MSF			BIT(7)
 /* Control register 3 */
 #define PCF2127_REG_CTRL3		0x02
 #define PCF2127_BIT_CTRL3_BLIE			BIT(0)
@@ -96,7 +97,8 @@
 #define PCF2127_CTRL2_IRQ_MASK ( \
 		PCF2127_BIT_CTRL2_AF | \
 		PCF2127_BIT_CTRL2_WDTF | \
-		PCF2127_BIT_CTRL2_TSF2)
+		PCF2127_BIT_CTRL2_TSF2 | \
+		PCF2127_BIT_CTRL2_MSF)

 #define PCF2127_MAX_TS_SUPPORTED	4

---
base-commit: 8f5ae30d69d7543eee0d70083daf4de8fe15d585
change-id: 20250825-rtc-irq-4d17b55204eb

Best regards,
-- 
Josua Mayer <josua@...id-run.com>