rtc: pcf8563: save battery power

According to Haoyu hym8563 datasheet this saves som power.  Might be
importat to battery life.  And maybe it works for the NXP part as well.

Signed-off-by: Jan Kardell <jan.kardell@telliq.com>
Cc: Alessandro Zummo <a.zummo@towertech.it>
Cc: Grant Likely <grant.likely@linaro.org>
Cc: Rob Herring <robh+dt@kernel.org>
Cc: Vincent Donnefort <vdonnefort@gmail.com>
Cc: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

drivers/rtc/rtc-pcf8563.c

@@ -42,6 +42,13 @@
 
 #define PCF8563_REG_CLKO	0x0D /* clock out */
 #define PCF8563_REG_TMRC	0x0E /* timer control */
+#define PCF8563_TMRC_ENABLE	BIT(7)
+#define PCF8563_TMRC_4096	0
+#define PCF8563_TMRC_64		1
+#define PCF8563_TMRC_1		2
+#define PCF8563_TMRC_1_60	3
+#define PCF8563_TMRC_MASK	3
+
 #define PCF8563_REG_TMR		0x0F /* timer */
 
 #define PCF8563_SC_LV		0x80 /* low voltage */
@@ -406,6 +413,7 @@ static int pcf8563_probe(struct i2c_client *client,
 {
 	struct pcf8563 *pcf8563;
 	int err;
+	unsigned char buf;
 
 	dev_dbg(&client->dev, "%s\n", __func__);
 
@@ -423,6 +431,14 @@ static int pcf8563_probe(struct i2c_client *client,
 	pcf8563->client = client;
 	device_set_wakeup_capable(&client->dev, 1);
 
+	/* Set timer to lowest frequency to save power (ref Haoyu datasheet) */
+	buf = PCF8563_TMRC_1_60;
+	err = pcf8563_write_block_data(client, PCF8563_REG_TMRC, 1, &buf);
+	if (err < 0) {
+		dev_err(&client->dev, "%s: write error\n", __func__);
+		return err;
+	}
+
 	pcf8563->rtc = devm_rtc_device_register(&client->dev,
 				pcf8563_driver.driver.name,
 				&pcf8563_rtc_ops, THIS_MODULE);