rtc: rs5c372: Fix reading from rtc when the oscillator got interrupted.

When the oscillator of the rtc gets interrupted,
e.g. due to an empty battery, reading from the rtc will now return an error
and the oscillator bit will be cleared, once the rtc is successfully reset.
Signed-off-by: Oliver Rohe <oliver.rohe@wago.com>
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>

drivers/rtc/rtc-rs5c372.c

@@ -52,8 +52,10 @@
 #	define RS5C_CTRL1_CT4		(4 << 0)	/* 1 Hz level irq */
 #define RS5C_REG_CTRL2		15
 #	define RS5C372_CTRL2_24		(1 << 5)
-#	define R2x2x_CTRL2_XSTP		(1 << 5)	/* only if R2x2x */
 #	define RS5C_CTRL2_XSTP		(1 << 4)	/* only if !R2x2x */
+#	define R2x2x_CTRL2_VDET		(1 << 6)	/* only if  R2x2x */
+#	define R2x2x_CTRL2_XSTP		(1 << 5)	/* only if  R2x2x */
+#	define R2x2x_CTRL2_PON		(1 << 4)	/* only if  R2x2x */
 #	define RS5C_CTRL2_CTFG		(1 << 2)
 #	define RS5C_CTRL2_AAFG		(1 << 1)	/* or WAFG */
 #	define RS5C_CTRL2_BAFG		(1 << 0)	/* or DAFG */
@@ -212,10 +214,27 @@ static int rs5c372_rtc_read_time(struct device *dev, struct rtc_time *tm)
 	struct i2c_client *client = to_i2c_client(dev);
 	struct rs5c372	*rs5c = i2c_get_clientdata(client);
 	int		status = rs5c_get_regs(rs5c);
+	unsigned char ctrl2 = rs5c->regs[RS5C_REG_CTRL2];
 
 	if (status < 0)
 		return status;
 
+	switch (rs5c->type) {
+	case rtc_r2025sd:
+	case rtc_r2221tl:
+		if ((rs5c->type == rtc_r2025sd && !(ctrl2 & R2x2x_CTRL2_XSTP)) ||
+		    (rs5c->type == rtc_r2221tl &&  (ctrl2 & R2x2x_CTRL2_XSTP))) {
+			dev_warn(&client->dev, "rtc oscillator interruption detected. Please reset the rtc clock.\n");
+			return -EINVAL;
+		}
+		break;
+	default:
+		if (ctrl2 & RS5C_CTRL2_XSTP) {
+			dev_warn(&client->dev, "rtc oscillator interruption detected. Please reset the rtc clock.\n");
+			return -EINVAL;
+		}
+	}
+
 	tm->tm_sec = bcd2bin(rs5c->regs[RS5C372_REG_SECS] & 0x7f);
 	tm->tm_min = bcd2bin(rs5c->regs[RS5C372_REG_MINS] & 0x7f);
 	tm->tm_hour = rs5c_reg2hr(rs5c, rs5c->regs[RS5C372_REG_HOURS]);
@@ -243,6 +262,7 @@ static int rs5c372_rtc_set_time(struct device *dev, struct rtc_time *tm)
 	struct i2c_client *client = to_i2c_client(dev);
 	struct rs5c372	*rs5c = i2c_get_clientdata(client);
 	unsigned char	buf[7];
+	unsigned char	ctrl2;
 	int		addr;
 
 	dev_dbg(&client->dev, "%s: tm is secs=%d, mins=%d, hours=%d "
@@ -261,7 +281,32 @@ static int rs5c372_rtc_set_time(struct device *dev, struct rtc_time *tm)
 	buf[6] = bin2bcd(tm->tm_year - 100);
 
 	if (i2c_smbus_write_i2c_block_data(client, addr, sizeof(buf), buf) < 0) {
-		dev_err(&client->dev, "%s: write error\n", __func__);
+		dev_dbg(&client->dev, "%s: write error in line %i\n",
+			__func__, __LINE__);
+		return -EIO;
+	}
+
+	addr = RS5C_ADDR(RS5C_REG_CTRL2);
+	ctrl2 = i2c_smbus_read_byte_data(client, addr);
+
+	/* clear rtc warning bits */
+	switch (rs5c->type) {
+	case rtc_r2025sd:
+	case rtc_r2221tl:
+		ctrl2 &= ~(R2x2x_CTRL2_VDET | R2x2x_CTRL2_PON);
+		if (rs5c->type == rtc_r2025sd)
+			ctrl2 |= R2x2x_CTRL2_XSTP;
+		else
+			ctrl2 &= ~R2x2x_CTRL2_XSTP;
+		break;
+	default:
+		ctrl2 &= ~RS5C_CTRL2_XSTP;
+		break;
+	}
+
+	if (i2c_smbus_write_byte_data(client, addr, ctrl2) < 0) {
+		dev_dbg(&client->dev, "%s: write error in line %i\n",
+			__func__, __LINE__);
 		return -EIO;
 	}
 
@@ -523,23 +568,18 @@ static int rs5c_oscillator_setup(struct rs5c372 *rs5c372)
 	buf[0] = rs5c372->regs[RS5C_REG_CTRL1];
 	buf[1] = rs5c372->regs[RS5C_REG_CTRL2];
 
-	/* handle xstp bit */
 	switch (rs5c372->type) {
 	case rtc_r2025sd:
 		if (buf[1] & R2x2x_CTRL2_XSTP)
 			return ret;
-		rs5c372->regs[RS5C_REG_CTRL2] |= R2x2x_CTRL2_XSTP;
 		break;
 	case rtc_r2221tl:
 		if (!(buf[1] & R2x2x_CTRL2_XSTP))
 			return ret;
-		rs5c372->regs[RS5C_REG_CTRL2] &= ~R2x2x_CTRL2_XSTP;
 		break;
-
 	default:
 		if (!(buf[1] & RS5C_CTRL2_XSTP))
 			return ret;
-		rs5c372->regs[RS5C_REG_CTRL2] &= ~RS5C_CTRL2_XSTP;
 		break;
 	}