Merge tag 'iio-fixes-for-3.19a' of git://git.kernel.org/pub/scm/linux/kernel/git/jic23/iio into staging-linus

Jonathan writes:

First round of IIO fixes for the 3.19 cycle.

* ad799x fix ad7991/ad7995/ad7999 setup as they do not have a configuration
  register to write to.  It is written during the convesion sequence. As
  such we don't want to write to it at other times.
* Fix iio_channel_read utility function to return to ensure it is apparent
  if the relevant element is not there. This avoids using a wrong value
  if some channels have the element and others do not.

drivers/iio/adc/ad799x.c

@@ -143,9 +143,15 @@ static int ad799x_write_config(struct ad799x_state *st, u16 val)
 	case ad7998:
 		return i2c_smbus_write_word_swapped(st->client, AD7998_CONF_REG,
 			val);
-	default:
+	case ad7992:
+	case ad7993:
+	case ad7994:
 		return i2c_smbus_write_byte_data(st->client, AD7998_CONF_REG,
 			val);
+	default:
+		/* Will be written when doing a conversion */
+		st->config = val;
+		return 0;
 	}
 }
 
@@ -155,8 +161,13 @@ static int ad799x_read_config(struct ad799x_state *st)
 	case ad7997:
 	case ad7998:
 		return i2c_smbus_read_word_swapped(st->client, AD7998_CONF_REG);
-	default:
+	case ad7992:
+	case ad7993:
+	case ad7994:
 		return i2c_smbus_read_byte_data(st->client, AD7998_CONF_REG);
+	default:
+		/* No readback support */
+		return st->config;
 	}
 }