rtc: add dm_rtc_write() helper

Similar to dm_rtc_read(), introduce a helper that allows the caller to
write multiple consecutive 8-bit registers with one call. If the
driver provides the ->write method, use that, otherwise loop using
->write8.
Reviewed-by: NSimon Glass <sjg@chromium.org>
Reviewed-by: NHeiko Schocher <hs@denx.de>
Signed-off-by: NRasmus Villemoes <rasmus.villemoes@prevas.dk>

drivers/rtc/rtc-uclass.c

@@ -59,6 +59,25 @@ int dm_rtc_read(struct udevice *dev, unsigned int reg, u8 *buf, unsigned int len
 	return 0;
 }
 
+int dm_rtc_write(struct udevice *dev, unsigned int reg,
+		 const u8 *buf, unsigned int len)
+{
+	struct rtc_ops *ops = rtc_get_ops(dev);
+
+	assert(ops);
+	if (ops->write)
+		return ops->write(dev, reg, buf, len);
+	if (!ops->write8)
+		return -ENOSYS;
+	while (len--) {
+		int ret = ops->write8(dev, reg++, *buf++);
+
+		if (ret < 0)
+			return ret;
+	}
+	return 0;
+}
+
 int rtc_read8(struct udevice *dev, unsigned int reg)
 {
 	struct rtc_ops *ops = rtc_get_ops(dev);

include/rtc.h

@@ -67,6 +67,18 @@ struct rtc_ops {
 	int (*read)(struct udevice *dev, unsigned int reg,
 		    u8 *buf, unsigned int len);
 
+	/**
+	 * write() - Write multiple 8-bit registers
+	 *
+	 * @dev:	Device to write to
+	 * @reg:	First register to write
+	 * @buf:	Input buffer
+	 * @len:	Number of registers to write
+	 * @return 0 if OK, -ve on error
+	 */
+	int (*write)(struct udevice *dev, unsigned int reg,
+		     const u8 *buf, unsigned int len);
+
 	/**
 	 * read8() - Read an 8-bit register
 	 *
@@ -132,6 +144,18 @@ int dm_rtc_reset(struct udevice *dev);
  */
 int dm_rtc_read(struct udevice *dev, unsigned int reg, u8 *buf, unsigned int len);
 
+/**
+ * dm_rtc_write() - Write multiple 8-bit registers
+ *
+ * @dev:	Device to write to
+ * @reg:	First register to write
+ * @buf:	Input buffer
+ * @len:	Number of registers to write
+ * @return 0 if OK, -ve on error
+ */
+int dm_rtc_write(struct udevice *dev, unsigned int reg,
+		 const u8 *buf, unsigned int len);
+
 /**
  * rtc_read8() - Read an 8-bit register
  *