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Message-ID: <e7a8d4fd0b9789ad890a2c92662a3a3051a0fba3.1757510157.git.akhilesh@ee.iitb.ac.in>
Date: Wed, 10 Sep 2025 19:24:48 +0530
From: Akhilesh Patil <akhilesh@...iitb.ac.in>
To: alexandre.belloni@...tlin.com, krzk+dt@...nel.org, robh@...nel.org,
conor+dt@...nel.org
Cc: skhan@...uxfoundation.org, linux-rtc@...r.kernel.org,
devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
akhileshpatilvnit@...il.com
Subject: [PATCH v2 6/6] rtc: m41t93: Add watchdog support
Implement watchdog feature for m41t93 rtc with 1s resolution.
Implement alarm only support (WDIOF_ALARMONLY) in this commit.
Define start, stop, ping, and set_timeout callbacks as needed
by the watchdog framework.
Use selftests/watchdog/watchdog-test kselftest for testing.
Observed IRQ pin(12) of rtc chip going low after late pinging
the watchdog.
Signed-off-by: Akhilesh Patil <akhilesh@...iitb.ac.in>
---
drivers/rtc/rtc-m41t93.c | 99 ++++++++++++++++++++++++++++++++++++++++
1 file changed, 99 insertions(+)
diff --git a/drivers/rtc/rtc-m41t93.c b/drivers/rtc/rtc-m41t93.c
index 4efd05b47597..d0eb069adb34 100644
--- a/drivers/rtc/rtc-m41t93.c
+++ b/drivers/rtc/rtc-m41t93.c
@@ -14,6 +14,7 @@
#include <linux/spi/spi.h>
#include <linux/regmap.h>
#include <linux/clk-provider.h>
+#include <linux/watchdog.h>
#define M41T93_REG_SSEC 0
#define M41T93_REG_ST_SEC 1
@@ -36,6 +37,10 @@
#define M41T93_SQW_RS_MASK 0xf0
#define M41T93_SQW_RS_SHIFT 4
#define M41T93_BIT_SQWE BIT(6)
+#define M41T93_REG_WATCHDOG 0x9
+#define M41T93_WDT_RB_MASK 0x3
+#define M41T93_WDT_BMB_MASK 0x7c
+#define M41T93_WDT_BMB_SHIFT 2
#define M41T93_REG_ALM_HOUR_HT 0xc
#define M41T93_REG_FLAGS 0xf
@@ -51,6 +56,9 @@ struct m41t93_data {
#ifdef CONFIG_COMMON_CLK
struct clk_hw clks;
#endif
+#ifdef CONFIG_WATCHDOG
+ struct watchdog_device wdd;
+#endif
};
static int m41t93_set_time(struct device *dev, struct rtc_time *tm)
@@ -412,6 +420,92 @@ static int rtc_m41t93_clks_register(struct device *dev, struct m41t93_data *m41t
}
#endif
+#ifdef CONFIG_WATCHDOG
+static int m41t93_wdt_ping(struct watchdog_device *wdd)
+{
+ u8 resolution, mult;
+ u8 val = 0;
+ int ret;
+ struct m41t93_data *m41t93 = watchdog_get_drvdata(wdd);
+
+ /* Resolution supported by hardware
+ * 0b00 : 1/16 seconds
+ * 0b01 : 1/4 second
+ * 0b10 : 1 second
+ * 0b11 : 4 seconds
+ */
+ resolution = 0x2; /* hardcode resolution to 1s */
+ mult = wdd->timeout;
+ val = resolution | (mult << M41T93_WDT_BMB_SHIFT & M41T93_WDT_BMB_MASK);
+
+ ret = regmap_write_bits(m41t93->regmap, M41T93_REG_WATCHDOG,
+ M41T93_WDT_RB_MASK | M41T93_WDT_BMB_MASK, val);
+
+ return ret;
+}
+
+static int m41t93_wdt_start(struct watchdog_device *wdd)
+{
+ return m41t93_wdt_ping(wdd);
+}
+
+static int m41t93_wdt_stop(struct watchdog_device *wdd)
+{
+ struct m41t93_data *m41t93 = watchdog_get_drvdata(wdd);
+
+ /* Write 0 to watchdog register */
+ return regmap_write_bits(m41t93->regmap, M41T93_REG_WATCHDOG,
+ M41T93_WDT_RB_MASK | M41T93_WDT_BMB_MASK, 0);
+}
+
+static int m41t93_wdt_set_timeout(struct watchdog_device *wdd,
+ unsigned int new_timeout)
+{
+ wdd->timeout = new_timeout;
+
+ return 0;
+}
+
+static const struct watchdog_info m41t93_wdt_info = {
+ .identity = "m41t93 rtc Watchdog",
+ .options = WDIOF_ALARMONLY | WDIOF_SETTIMEOUT | WDIOF_KEEPALIVEPING,
+};
+
+static const struct watchdog_ops m41t93_watchdog_ops = {
+ .owner = THIS_MODULE,
+ .start = m41t93_wdt_start,
+ .stop = m41t93_wdt_stop,
+ .ping = m41t93_wdt_ping,
+ .set_timeout = m41t93_wdt_set_timeout,
+};
+
+static int m41t93_watchdog_register(struct device *dev, struct m41t93_data *m41t93)
+{
+ int ret;
+
+ m41t93->wdd.parent = dev;
+ m41t93->wdd.info = &m41t93_wdt_info;
+ m41t93->wdd.ops = &m41t93_watchdog_ops;
+ m41t93->wdd.min_timeout = 0;
+ m41t93->wdd.max_timeout = 10;
+ m41t93->wdd.timeout = 3; /* Default timeout is 3 sec */
+ m41t93->wdd.status = WATCHDOG_NOWAYOUT_INIT_STATUS;
+
+ watchdog_set_drvdata(&m41t93->wdd, m41t93);
+
+ ret = devm_watchdog_register_device(dev, &m41t93->wdd);
+ if (ret) {
+ dev_warn(dev, "Failed to register watchdog\n");
+ return ret;
+ }
+
+ /* Disable watchdog at start */
+ ret = m41t93_wdt_stop(&m41t93->wdd);
+
+ return ret;
+}
+#endif
+
static struct spi_driver m41t93_driver;
static const struct regmap_config regmap_config = {
@@ -465,6 +559,11 @@ static int m41t93_probe(struct spi_device *spi)
if (ret)
dev_warn(&spi->dev, "Unable to register clock\n");
#endif
+#ifdef CONFIG_WATCHDOG
+ ret = m41t93_watchdog_register(&spi->dev, m41t93);
+ if (ret)
+ dev_warn(&spi->dev, "Unable to register watchdog\n");
+#endif
return 0;
}
--
2.34.1
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