rtc-pcf8563-guf: prevent resetting of TIE bit to support bootselect

Save the value of TIE bit value before resetting CONTROL_STATUS_2 register in
probe() routine of PCF8563 driver. Otherwise, a bootselect functionality stops
working because it stores some information across reboot in RTC registers.

Signed-off-by: Mikhail Vanyulin <mikhail.vanyulin@rtsoft.de>

recipes-kernel/modules/rtc-pcf8563-guf/rtc-pcf8563-guf.c

@@ -23,6 +23,7 @@
 
 #define PCF8563_REG_ST1		0x00 /* status */
 #define PCF8563_REG_ST2		0x01
+#define PCF8563_BIT_TIE		BIT(0)
 #define PCF8563_BIT_AIE		BIT(1)
 #define PCF8563_BIT_AF		BIT(3)
 #define PCF8563_BITS_ST2_N	(7 << 5)
@@ -561,6 +562,17 @@ static int pcf8563_probe(struct i2c_client *client,
 
 	/* Clear flags and disable interrupts */
 	buf = 0;
+
+	/* SECO Northern Europe systems use the TIE bit for bootselect storage.
+	   So, we do not reset it.
+	 */
+	err = pcf8563_read_block_data(client, PCF8563_REG_ST2, 1, &buf);
+	if (err < 0) {
+		dev_err(&client->dev, "%s: read error\n", __func__);
+		return err;
+	}
+	buf &= PCF8563_BIT_TIE;
+
 	err = pcf8563_write_block_data(client, PCF8563_REG_ST2, 1, &buf);
 	if (err < 0) {
 		dev_err(&client->dev, "%s: write error\n", __func__);