[PATCH v4 6/6] iio: dac: ad5504: support scale via output-range-microvolt property

[Taha Ed-Dafili <0rayn.dev@gmail.com>]

The AD5504/AD5501 output range (0-30V or 0-60V) is determined by the
hardware R_SEL pin and is required to compute IIO_CHAN_INFO_SCALE
correctly. Previously the driver derived this solely from the vcc
regulator's configured voltage, which conflated the supply voltage
with the DAC's actual output range and offered no way to express the
range explicitly in firmware.

Add support for the standard 'output-range-microvolt' device property,
validating that it specifies one of the two supported ranges (0-30V
or 0-60V) and using it to set st->vref_mv directly. When this property
is present, the vcc regulator is only enabled (not read) via
devm_regulator_get_enable(), since the regulator's actual voltage is
no longer the source of truth for the output range.

For backward compatibility with older device trees that predate this
property, fall back to reading the vcc regulator's configured voltage
via devm_regulator_get_enable_read_voltage() when
'output-range-microvolt' is absent.

Use device_property_present() to explicitly distinguish "property
absent" from "property present but malformed", rather than relying on
the -EINVAL return from device_property_read_u32_array() as an
absence sentinel. That return code is ambiguous: it is also returned
when the property exists but the parsed array size does not match the
expected length, which would have silently and incorrectly routed a
malformed property through the legacy regulator-voltage fallback
instead of surfacing a clear validation error.

Signed-off-by: Taha Ed-Dafili <0rayn.dev@gmail.com>
---
 drivers/iio/dac/ad5504.c | 32 ++++++++++++++++++++++++++------
 1 file changed, 26 insertions(+), 6 deletions(-)

diff --git a/drivers/iio/dac/ad5504.c b/drivers/iio/dac/ad5504.c
index 546420f9afc0..25c0744545f0 100644
--- a/drivers/iio/dac/ad5504.c
+++ b/drivers/iio/dac/ad5504.c
@@ -15,6 +15,7 @@
 #include <linux/mod_devicetable.h>
 #include <linux/module.h>
 #include <linux/mutex.h>
+#include <linux/property.h>
 #include <linux/regulator/consumer.h>
 #include <linux/spi/spi.h>
 #include <linux/sysfs.h>
@@ -293,6 +294,7 @@ static int ad5504_probe(struct spi_device *spi)
 	struct device *dev = &spi->dev;
 	struct iio_dev *indio_dev;
 	struct ad5504_state *st;
+	u32 range[2];
 	int ret;
 
 	indio_dev = devm_iio_device_alloc(dev, sizeof(*st));
@@ -308,12 +310,30 @@ static int ad5504_probe(struct spi_device *spi)
 	if (ACPI_COMPANION(dev)) {
 		st->vref_mv = AD5504_VA_MV_ACPI_DEFAULT;
 	} else {
-		ret = devm_regulator_get_enable_read_voltage(dev, "vcc");
-		if (ret < 0)
-			return dev_err_probe(dev, ret,
-					     "Failed to get vcc regulator\n");
-
-		st->vref_mv = ret / MILLI;
+		if (device_property_present(dev, "output-range-microvolt")) {
+			ret = device_property_read_u32_array(dev, "output-range-microvolt",
+							     range, ARRAY_SIZE(range));
+			if (ret)
+				return dev_err_probe(dev, ret,
+							"Error parsing output-range-microvolt\n");
+
+			if (range[0] != 0 || (range[1] != 30 * MICRO && range[1] != 60 * MICRO))
+				return dev_err_probe(dev, -EINVAL,
+					"Invalid output-range-microvolt\n");
+
+			st->vref_mv = range[1] / MILLI;
+
+			ret = devm_regulator_get_enable(dev, "vcc");
+			if (ret < 0)
+				return dev_err_probe(dev, ret, "Failed to enable vcc regulator\n");
+		} else {
+			/* Backward compat: old DTs without output-range-microvolt */
+			ret = devm_regulator_get_enable_read_voltage(dev, "vcc");
+			if (ret < 0)
+				return dev_err_probe(dev, ret, "Failed to get vcc regulator\n");
+
+			st->vref_mv = ret / MILLI;
+		}
 	}
 
 	st->spi = spi;
-- 
2.55.0