rtc: pcf2127: add tamper detection support

Add support for integrated tamper detection function in both PCF2127 and
PCF2129 chips. This patch implements the feature by adding an additional
timestamp0 file to sysfs device path. This file contains seconds since
epoch, if an event occurred, or is empty, if none occurred.
Interface should match ISL1208 and RV3028 RTC drivers.

Signed-off-by: Bruno Thomsen <bruno.thomsen@gmail.com>
Link: https://lore.kernel.org/r/20190822131936.18772-5-bruno.thomsen@gmail.com
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>

drivers/rtc/rtc-pcf2127.c

@@ -25,11 +25,18 @@
 
 /* Control register 1 */
 #define PCF2127_REG_CTRL1		0x00
+#define PCF2127_BIT_CTRL1_TSF1			BIT(4)
 /* Control register 2 */
 #define PCF2127_REG_CTRL2		0x01
+#define PCF2127_BIT_CTRL2_TSIE			BIT(2)
+#define PCF2127_BIT_CTRL2_TSF2			BIT(5)
 /* Control register 3 */
 #define PCF2127_REG_CTRL3		0x02
+#define PCF2127_BIT_CTRL3_BLIE			BIT(0)
+#define PCF2127_BIT_CTRL3_BIE			BIT(1)
 #define PCF2127_BIT_CTRL3_BLF			BIT(2)
+#define PCF2127_BIT_CTRL3_BF			BIT(3)
+#define PCF2127_BIT_CTRL3_BTSE			BIT(4)
 /* Time and date registers */
 #define PCF2127_REG_SC			0x03
 #define PCF2127_BIT_SC_OSF			BIT(7)
@@ -46,6 +53,16 @@
 #define PCF2127_BIT_WD_CTL_CD0			BIT(6)
 #define PCF2127_BIT_WD_CTL_CD1			BIT(7)
 #define PCF2127_REG_WD_VAL		0x11
+/* Tamper timestamp registers */
+#define PCF2127_REG_TS_CTRL		0x12
+#define PCF2127_BIT_TS_CTRL_TSOFF		BIT(6)
+#define PCF2127_BIT_TS_CTRL_TSM			BIT(7)
+#define PCF2127_REG_TS_SC		0x13
+#define PCF2127_REG_TS_MN		0x14
+#define PCF2127_REG_TS_HR		0x15
+#define PCF2127_REG_TS_DM		0x16
+#define PCF2127_REG_TS_MO		0x17
+#define PCF2127_REG_TS_YR		0x18
 /*
  * RAM registers
  * PCF2127 has 512 bytes general-purpose static RAM (SRAM) that is
@@ -305,6 +322,97 @@ static const struct watchdog_ops pcf2127_watchdog_ops = {
 	.set_timeout = pcf2127_wdt_set_timeout,
 };
 
+/* sysfs interface */
+
+static ssize_t timestamp0_store(struct device *dev,
+				struct device_attribute *attr,
+				const char *buf, size_t count)
+{
+	struct pcf2127 *pcf2127 = dev_get_drvdata(dev->parent);
+	int ret;
+
+	ret = regmap_update_bits(pcf2127->regmap, PCF2127_REG_CTRL1,
+				 PCF2127_BIT_CTRL1_TSF1, 0);
+	if (ret) {
+		dev_err(dev, "%s: update ctrl1 ret=%d\n", __func__, ret);
+		return ret;
+	}
+
+	ret = regmap_update_bits(pcf2127->regmap, PCF2127_REG_CTRL2,
+				 PCF2127_BIT_CTRL2_TSF2, 0);
+	if (ret) {
+		dev_err(dev, "%s: update ctrl2 ret=%d\n", __func__, ret);
+		return ret;
+	}
+
+	ret = pcf2127_wdt_active_ping(&pcf2127->wdd);
+	if (ret)
+		return ret;
+
+	return count;
+};
+
+static ssize_t timestamp0_show(struct device *dev,
+			       struct device_attribute *attr, char *buf)
+{
+	struct pcf2127 *pcf2127 = dev_get_drvdata(dev->parent);
+	struct rtc_time tm;
+	int ret;
+	unsigned char data[25];
+
+	ret = regmap_bulk_read(pcf2127->regmap, PCF2127_REG_CTRL1, data,
+			       sizeof(data));
+	if (ret) {
+		dev_err(dev, "%s: read error ret=%d\n", __func__, ret);
+		return ret;
+	}
+
+	dev_dbg(dev,
+		"%s: raw data is cr1=%02x, cr2=%02x, cr3=%02x, ts_sc=%02x, "
+		"ts_mn=%02x, ts_hr=%02x, ts_dm=%02x, ts_mo=%02x, ts_yr=%02x\n",
+		__func__, data[PCF2127_REG_CTRL1], data[PCF2127_REG_CTRL2],
+		data[PCF2127_REG_CTRL3], data[PCF2127_REG_TS_SC],
+		data[PCF2127_REG_TS_MN], data[PCF2127_REG_TS_HR],
+		data[PCF2127_REG_TS_DM], data[PCF2127_REG_TS_MO],
+		data[PCF2127_REG_TS_YR]);
+
+	ret = pcf2127_wdt_active_ping(&pcf2127->wdd);
+	if (ret)
+		return ret;
+
+	if (!(data[PCF2127_REG_CTRL1] & PCF2127_BIT_CTRL1_TSF1) &&
+	    !(data[PCF2127_REG_CTRL2] & PCF2127_BIT_CTRL2_TSF2))
+		return 0;
+
+	tm.tm_sec = bcd2bin(data[PCF2127_REG_TS_SC] & 0x7F);
+	tm.tm_min = bcd2bin(data[PCF2127_REG_TS_MN] & 0x7F);
+	tm.tm_hour = bcd2bin(data[PCF2127_REG_TS_HR] & 0x3F);
+	tm.tm_mday = bcd2bin(data[PCF2127_REG_TS_DM] & 0x3F);
+	/* TS_MO register (month) value range: 1-12 */
+	tm.tm_mon = bcd2bin(data[PCF2127_REG_TS_MO] & 0x1F) - 1;
+	tm.tm_year = bcd2bin(data[PCF2127_REG_TS_YR]);
+	if (tm.tm_year < 70)
+		tm.tm_year += 100; /* assume we are in 1970...2069 */
+
+	ret = rtc_valid_tm(&tm);
+	if (ret)
+		return ret;
+
+	return sprintf(buf, "%llu\n",
+		       (unsigned long long)rtc_tm_to_time64(&tm));
+};
+
+static DEVICE_ATTR_RW(timestamp0);
+
+static struct attribute *pcf2127_attrs[] = {
+	&dev_attr_timestamp0.attr,
+	NULL
+};
+
+static const struct attribute_group pcf2127_attr_group = {
+	.attrs	= pcf2127_attrs,
+};
+
 static int pcf2127_probe(struct device *dev, struct regmap *regmap,
 			const char *name, bool has_nvmem)
 {
@@ -371,6 +479,58 @@ static int pcf2127_probe(struct device *dev, struct regmap *regmap,
 	if (ret)
 		return ret;
 
+	/*
+	 * Disable battery low/switch-over timestamp and interrupts.
+	 * Clear battery interrupt flags which can block new trigger events.
+	 * Note: This is the default chip behaviour but added to ensure
+	 * correct tamper timestamp and interrupt function.
+	 */
+	ret = regmap_update_bits(pcf2127->regmap, PCF2127_REG_CTRL3,
+				 PCF2127_BIT_CTRL3_BTSE |
+				 PCF2127_BIT_CTRL3_BF |
+				 PCF2127_BIT_CTRL3_BIE |
+				 PCF2127_BIT_CTRL3_BLIE, 0);
+	if (ret) {
+		dev_err(dev, "%s: interrupt config (ctrl3) failed\n",
+			__func__);
+		return ret;
+	}
+
+	/*
+	 * Enable timestamp function and store timestamp of first trigger
+	 * event until TSF1 and TFS2 interrupt flags are cleared.
+	 */
+	ret = regmap_update_bits(pcf2127->regmap, PCF2127_REG_TS_CTRL,
+				 PCF2127_BIT_TS_CTRL_TSOFF |
+				 PCF2127_BIT_TS_CTRL_TSM,
+				 PCF2127_BIT_TS_CTRL_TSM);
+	if (ret) {
+		dev_err(dev, "%s: tamper detection config (ts_ctrl) failed\n",
+			__func__);
+		return ret;
+	}
+
+	/*
+	 * Enable interrupt generation when TSF1 or TSF2 timestamp flags
+	 * are set. Interrupt signal is an open-drain output and can be
+	 * left floating if unused.
+	 */
+	ret = regmap_update_bits(pcf2127->regmap, PCF2127_REG_CTRL2,
+				 PCF2127_BIT_CTRL2_TSIE,
+				 PCF2127_BIT_CTRL2_TSIE);
+	if (ret) {
+		dev_err(dev, "%s: tamper detection config (ctrl2) failed\n",
+			__func__);
+		return ret;
+	}
+
+	ret = rtc_add_group(pcf2127->rtc, &pcf2127_attr_group);
+	if (ret) {
+		dev_err(dev, "%s: tamper sysfs registering failed\n",
+			__func__);
+		return ret;
+	}
+
 	return rtc_register_device(pcf2127->rtc);
 }