dm: rtc: Add 16-bit read/write support

At present there are only 8-bit and 32-bit read/write routines in
the rtc uclass driver. This adds the 16-bit support.

Signed-off-by: Bin Meng <bmeng.cn@gmail.com>
Reviewed-by: Simon Glass <sjg@chromium.org>

drivers/rtc/rtc-uclass.c

@@ -60,6 +60,36 @@ int rtc_write8(struct udevice *dev, unsigned int reg, int val)
 	return ops->write8(dev, reg, val);
 }
 
+int rtc_read16(struct udevice *dev, unsigned int reg, u16 *valuep)
+{
+	u16 value = 0;
+	int ret;
+	int i;
+
+	for (i = 0; i < sizeof(value); i++) {
+		ret = rtc_read8(dev, reg + i);
+		if (ret < 0)
+			return ret;
+		value |= ret << (i << 3);
+	}
+
+	*valuep = value;
+	return 0;
+}
+
+int rtc_write16(struct udevice *dev, unsigned int reg, u16 value)
+{
+	int i, ret;
+
+	for (i = 0; i < sizeof(value); i++) {
+		ret = rtc_write8(dev, reg + i, (value >> (i << 3)) & 0xff);
+		if (ret)
+			return ret;
+	}
+
+	return 0;
+}
+
 int rtc_read32(struct udevice *dev, unsigned int reg, u32 *valuep)
 {
 	u32 value = 0;

include/rtc.h

@@ -127,6 +127,26 @@ int rtc_read8(struct udevice *dev, unsigned int reg);
  */
 int rtc_write8(struct udevice *dev, unsigned int reg, int val);
 
+/**
+ * rtc_read16() - Read a 16-bit value from the RTC
+ *
+ * @dev:	Device to read from
+ * @reg:	Offset to start reading from
+ * @valuep:	Place to put the value that is read
+ * @return 0 if OK, -ve on error
+ */
+int rtc_read16(struct udevice *dev, unsigned int reg, u16 *valuep);
+
+/**
+ * rtc_write16() - Write a 16-bit value to the RTC
+ *
+ * @dev:	Device to write to
+ * @reg:	Register to start writing to
+ * @value:	Value to write
+ * @return 0 if OK, -ve on error
+ */
+int rtc_write16(struct udevice *dev, unsigned int reg, u16 value);
+
 /**
  * rtc_read32() - Read a 32-bit value from the RTC
  *