Third set of fixes for IIO in the 4.7 cycle.

A couple of really old bugs and the results of Mark taking a close look at
 some nasty regulator handling.
 
 * ad7266
   - Fix broken regulator handling that won't play well with dummy regulators.
   - Correctly handle and optional regulator.
   - Fix probe deferral for the vref regulator.
 * kxsd9
   - Fix a wrong error check that leads to an inability to write or read
   the scale.
 * sca3000
   - Fix a wrong error check that leads to an inability to read back the
   sampling frequency.
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Merge tag 'iio-fixes-for-4.7c' of git://git.kernel.org/pub/scm/linux/kernel/git/jic23/iio into staging-linus

Jonathan writes:

Third set of fixes for IIO in the 4.7 cycle.

A couple of really old bugs and the results of Mark taking a close look at
some nasty regulator handling.

* ad7266
  - Fix broken regulator handling that won't play well with dummy regulators.
  - Correctly handle and optional regulator.
  - Fix probe deferral for the vref regulator.
* kxsd9
  - Fix a wrong error check that leads to an inability to write or read
  the scale.
* sca3000
  - Fix a wrong error check that leads to an inability to read back the
  sampling frequency.

drivers/iio/accel/kxsd9.c

@@ -81,7 +81,7 @@ static int kxsd9_write_scale(struct iio_dev *indio_dev, int micro)
 
 	mutex_lock(&st->buf_lock);
 	ret = spi_w8r8(st->us, KXSD9_READ(KXSD9_REG_CTRL_C));
-	if (ret)
+	if (ret < 0)
 		goto error_ret;
 	st->tx[0] = KXSD9_WRITE(KXSD9_REG_CTRL_C);
 	st->tx[1] = (ret & ~KXSD9_FS_MASK) | i;
@@ -163,7 +163,7 @@ static int kxsd9_read_raw(struct iio_dev *indio_dev,
 		break;
 	case IIO_CHAN_INFO_SCALE:
 		ret = spi_w8r8(st->us, KXSD9_READ(KXSD9_REG_CTRL_C));
-		if (ret)
+		if (ret < 0)
 			goto error_ret;
 		*val2 = kxsd9_micro_scales[ret & KXSD9_FS_MASK];
 		ret = IIO_VAL_INT_PLUS_MICRO;

drivers/iio/adc/ad7266.c

@@ -396,8 +396,8 @@ static int ad7266_probe(struct spi_device *spi)
 
 	st = iio_priv(indio_dev);
 
-	st->reg = devm_regulator_get(&spi->dev, "vref");
-	if (!IS_ERR_OR_NULL(st->reg)) {
+	st->reg = devm_regulator_get_optional(&spi->dev, "vref");
+	if (!IS_ERR(st->reg)) {
 		ret = regulator_enable(st->reg);
 		if (ret)
 			return ret;
@@ -408,6 +408,9 @@ static int ad7266_probe(struct spi_device *spi)
 
 		st->vref_mv = ret / 1000;
 	} else {
+		/* Any other error indicates that the regulator does exist */
+		if (PTR_ERR(st->reg) != -ENODEV)
+			return PTR_ERR(st->reg);
 		/* Use internal reference */
 		st->vref_mv = 2500;
 	}

drivers/staging/iio/accel/sca3000_core.c

@@ -594,7 +594,7 @@ static ssize_t sca3000_read_frequency(struct device *dev,
 		goto error_ret_mut;
 	ret = sca3000_read_ctrl_reg(st, SCA3000_REG_CTRL_SEL_OUT_CTRL);
 	mutex_unlock(&st->lock);
-	if (ret)
+	if (ret < 0)
 		goto error_ret;
 	val = ret;
 	if (base_freq > 0)