dm: i2c: Add functions to read and write a register

Add driver model versions of the legacy functions to read and write a
single byte register. These are a useful shortcut in many cases.

Signed-off-by: Simon Glass <sjg@chromium.org>
Acked-by: Heiko Schocher <hs@denx.de>

drivers/i2c/i2c-uclass.c

@@ -186,6 +186,25 @@ int dm_i2c_write(struct udevice *dev, uint offset, const uint8_t *buffer,
 	}
 }
 
+int dm_i2c_reg_read(struct udevice *dev, uint offset)
+{
+	uint8_t val;
+	int ret;
+
+	ret = dm_i2c_read(dev, offset, &val, 1);
+	if (ret < 0)
+		return ret;
+
+	return val;
+}
+
+int dm_i2c_reg_write(struct udevice *dev, uint offset, uint value)
+{
+	uint8_t val = value;
+
+	return dm_i2c_write(dev, offset, &val, 1);
+}
+
 /**
  * i2c_probe_chip() - probe for a chip on a bus
  *

include/i2c.h

@@ -124,6 +124,27 @@ int dm_i2c_probe(struct udevice *bus, uint chip_addr, uint chip_flags,
 		 struct udevice **devp);
 
 /**
+ * dm_i2c_reg_read() - Read a value from an I2C register
+ *
+ * This reads a single value from the given address in an I2C chip
+ *
+ * @addr:	Address to read from
+ * @return value read, or -ve on error
+ */
+int dm_i2c_reg_read(struct udevice *dev, uint offset);
+
+/**
+ * dm_i2c_reg_write() - Write a value to an I2C register
+ *
+ * This writes a single value to the given address in an I2C chip
+ *
+ * @addr:	Address to write to
+ * @val:	Value to write (normally a byte)
+ * @return 0 on success, -ve on error
+ */
+int dm_i2c_reg_write(struct udevice *dev, uint offset, unsigned int val);
+
+/**
  * dm_i2c_set_bus_speed() - set the speed of a bus
  *
  * @bus:	Bus to adjust