rtc: abx80x: add basic watchdog support

The abx804 and abx805 chips have support for a simple watchdog
function that can trigger an external reset.

Signed-off-by: Jeremy Gebben <jgebben@sweptlaser.com>
Reviewed-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>

drivers/rtc/Kconfig

@@ -187,6 +187,7 @@ config RTC_DRV_ABB5ZES3
 
 config RTC_DRV_ABX80X
 	tristate "Abracon ABx80x"
+	select WATCHDOG_CORE if WATCHDOG
 	help
 	  If you say yes here you get support for Abracon AB080X and AB180X
 	  families of ultra-low-power  battery- and capacitor-backed real-time

drivers/rtc/rtc-abx80x.c

@@ -17,6 +17,7 @@
 #include <linux/i2c.h>
 #include <linux/module.h>
 #include <linux/rtc.h>
+#include <linux/watchdog.h>
 
 #define ABX8XX_REG_HTH		0x00
 #define ABX8XX_REG_SC		0x01
@@ -37,6 +38,7 @@
 
 #define ABX8XX_REG_STATUS	0x0f
 #define ABX8XX_STATUS_AF	BIT(2)
+#define ABX8XX_STATUS_WDT	BIT(6)
 
 #define ABX8XX_REG_CTRL1	0x10
 #define ABX8XX_CTRL_WRITE	BIT(0)
@@ -61,6 +63,14 @@
 #define ABX8XX_OSS_OF		BIT(1)
 #define ABX8XX_OSS_OMODE	BIT(4)
 
+#define ABX8XX_REG_WDT		0x1b
+#define ABX8XX_WDT_WDS		BIT(7)
+#define ABX8XX_WDT_BMB_MASK	0x7c
+#define ABX8XX_WDT_BMB_SHIFT	2
+#define ABX8XX_WDT_MAX_TIME	(ABX8XX_WDT_BMB_MASK >> ABX8XX_WDT_BMB_SHIFT)
+#define ABX8XX_WDT_WRB_MASK	0x03
+#define ABX8XX_WDT_WRB_1HZ	0x02
+
 #define ABX8XX_REG_CFG_KEY	0x1f
 #define ABX8XX_CFG_KEY_OSC	0xa1
 #define ABX8XX_CFG_KEY_MISC	0x9d
@@ -80,23 +90,25 @@ enum abx80x_chip {AB0801, AB0803, AB0804, AB0805,
 struct abx80x_cap {
 	u16 pn;
 	bool has_tc;
+	bool has_wdog;
 };
 
 static struct abx80x_cap abx80x_caps[] = {
 	[AB0801] = {.pn = 0x0801},
 	[AB0803] = {.pn = 0x0803},
-	[AB0804] = {.pn = 0x0804, .has_tc = true},
-	[AB0805] = {.pn = 0x0805, .has_tc = true},
+	[AB0804] = {.pn = 0x0804, .has_tc = true, .has_wdog = true},
+	[AB0805] = {.pn = 0x0805, .has_tc = true, .has_wdog = true},
 	[AB1801] = {.pn = 0x1801},
 	[AB1803] = {.pn = 0x1803},
-	[AB1804] = {.pn = 0x1804, .has_tc = true},
-	[AB1805] = {.pn = 0x1805, .has_tc = true},
+	[AB1804] = {.pn = 0x1804, .has_tc = true, .has_wdog = true},
+	[AB1805] = {.pn = 0x1805, .has_tc = true, .has_wdog = true},
 	[ABX80X] = {.pn = 0}
 };
 
 struct abx80x_priv {
 	struct rtc_device *rtc;
 	struct i2c_client *client;
+	struct watchdog_device wdog;
 };
 
 static int abx80x_is_rc_mode(struct i2c_client *client)
@@ -234,6 +246,13 @@ static irqreturn_t abx80x_handle_irq(int irq, void *dev_id)
 	if (status & ABX8XX_STATUS_AF)
 		rtc_update_irq(rtc, 1, RTC_AF | RTC_IRQF);
 
+	/*
+	 * It is unclear if we'll get an interrupt before the external
+	 * reset kicks in.
+	 */
+	if (status & ABX8XX_STATUS_WDT)
+		dev_alert(&client->dev, "watchdog timeout interrupt.\n");
+
 	i2c_smbus_write_byte_data(client, ABX8XX_REG_STATUS, 0);
 
 	return IRQ_HANDLED;
@@ -535,6 +554,89 @@ static void rtc_calib_remove_sysfs_group(void *_dev)
 	sysfs_remove_group(&dev->kobj, &rtc_calib_attr_group);
 }
 
+#ifdef CONFIG_WATCHDOG
+
+static inline u8 timeout_bits(unsigned int timeout)
+{
+	return ((timeout << ABX8XX_WDT_BMB_SHIFT) & ABX8XX_WDT_BMB_MASK) |
+		 ABX8XX_WDT_WRB_1HZ;
+}
+
+static int __abx80x_wdog_set_timeout(struct watchdog_device *wdog,
+				     unsigned int timeout)
+{
+	struct abx80x_priv *priv = watchdog_get_drvdata(wdog);
+	u8 val = ABX8XX_WDT_WDS | timeout_bits(timeout);
+
+	/*
+	 * Writing any timeout to the WDT register resets the watchdog timer.
+	 * Writing 0 disables it.
+	 */
+	return i2c_smbus_write_byte_data(priv->client, ABX8XX_REG_WDT, val);
+}
+
+static int abx80x_wdog_set_timeout(struct watchdog_device *wdog,
+				   unsigned int new_timeout)
+{
+	int err = 0;
+
+	if (watchdog_hw_running(wdog))
+		err = __abx80x_wdog_set_timeout(wdog, new_timeout);
+
+	if (err == 0)
+		wdog->timeout = new_timeout;
+
+	return err;
+}
+
+static int abx80x_wdog_ping(struct watchdog_device *wdog)
+{
+	return __abx80x_wdog_set_timeout(wdog, wdog->timeout);
+}
+
+static int abx80x_wdog_start(struct watchdog_device *wdog)
+{
+	return __abx80x_wdog_set_timeout(wdog, wdog->timeout);
+}
+
+static int abx80x_wdog_stop(struct watchdog_device *wdog)
+{
+	return __abx80x_wdog_set_timeout(wdog, 0);
+}
+
+static const struct watchdog_info abx80x_wdog_info = {
+	.identity = "abx80x watchdog",
+	.options = WDIOF_KEEPALIVEPING | WDIOF_SETTIMEOUT | WDIOF_MAGICCLOSE,
+};
+
+static const struct watchdog_ops abx80x_wdog_ops = {
+	.owner = THIS_MODULE,
+	.start = abx80x_wdog_start,
+	.stop = abx80x_wdog_stop,
+	.ping = abx80x_wdog_ping,
+	.set_timeout = abx80x_wdog_set_timeout,
+};
+
+static int abx80x_setup_watchdog(struct abx80x_priv *priv)
+{
+	priv->wdog.parent = &priv->client->dev;
+	priv->wdog.ops = &abx80x_wdog_ops;
+	priv->wdog.info = &abx80x_wdog_info;
+	priv->wdog.min_timeout = 1;
+	priv->wdog.max_timeout = ABX8XX_WDT_MAX_TIME;
+	priv->wdog.timeout = ABX8XX_WDT_MAX_TIME;
+
+	watchdog_set_drvdata(&priv->wdog, priv);
+
+	return devm_watchdog_register_device(&priv->client->dev, &priv->wdog);
+}
+#else
+static int abx80x_setup_watchdog(struct abx80x_priv *priv)
+{
+	return 0;
+}
+#endif
+
 static int abx80x_probe(struct i2c_client *client,
 			const struct i2c_device_id *id)
 {
@@ -629,6 +731,12 @@ static int abx80x_probe(struct i2c_client *client,
 
 	i2c_set_clientdata(client, priv);
 
+	if (abx80x_caps[part].has_wdog) {
+		err = abx80x_setup_watchdog(priv);
+		if (err)
+			return err;
+	}
+
 	if (client->irq > 0) {
 		dev_info(&client->dev, "IRQ %d supplied\n", client->irq);
 		err = devm_request_threaded_irq(&client->dev, client->irq, NULL,