Parse optional maxim,rfs-ohms values to derive the per-channel output
current scale (mA per step) for the IIO current ABI.
Select per-variant parameters to match the shared register map while
handling different data widths and full-scale current calculations.
Behavior changes:
- If maxim,rfs-ohms is present, IIO_CHAN_INFO_SCALE becomes available
and reports mA/step derived from Rfs.
- If maxim,rfs-ohms is missing, SCALE is not exposed to keep older DTs
working without requiring updates.
- RAW writes are now limited to the representable sign-magnitude range
of the detected variant to avoid silent truncation (e.g. +/-31 on
DS440x).
Signed-off-by: Oleksij Rempel <o.rempel@pengutronix.de>
---
drivers/iio/dac/ds4424.c | 137 +++++++++++++++++++++++++++++++++++++--
1 file changed, 132 insertions(+), 5 deletions(-)
diff --git a/drivers/iio/dac/ds4424.c b/drivers/iio/dac/ds4424.c
index 9c24c37d3c42..a0c60eb89717 100644
--- a/drivers/iio/dac/ds4424.c
+++ b/drivers/iio/dac/ds4424.c
@@ -8,6 +8,7 @@
#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/i2c.h>
+#include <linux/property.h>
#include <linux/regulator/consumer.h>
#include <linux/err.h>
#include <linux/delay.h>
@@ -54,12 +55,41 @@ enum ds4424_device_ids {
ID_DS4424,
};
+/*
+ * Two variant groups share the same register map but differ in:
+ * - resolution/data mask (DS4402/DS4404: 5-bit, DS4422/DS4424: 7-bit)
+ * - full-scale current calculation (different Vref and divider)
+ * Addressing also differs (DS440x tri-level, DS442x bi-level), but is
+ * handled via board configuration, not driver logic.
+ */
+struct ds4424_chip_info {
+ u8 result_mask;
+ int vref_mv;
+ int scale_denom;
+};
+
+static const struct ds4424_chip_info ds4424_info = {
+ .result_mask = 0x7F,
+ .vref_mv = 976,
+ .scale_denom = 16,
+};
+
+/* DS4402 is handled like DS4404 (same resolution and scale formula). */
+static const struct ds4424_chip_info ds4404_info = {
+ .result_mask = 0x1F,
+ .vref_mv = 1230,
+ .scale_denom = 4,
+};
+
struct ds4424_data {
struct i2c_client *client;
struct mutex lock;
uint8_t save[DS4424_MAX_DAC_CHANNELS];
struct regulator *vcc_reg;
uint8_t raw[DS4424_MAX_DAC_CHANNELS];
+ const struct ds4424_chip_info *chip_info;
+ u32 rfs_ohms[DS4424_MAX_DAC_CHANNELS];
+ bool has_rfs;
};
static const struct iio_chan_spec ds4424_channels[] = {
@@ -111,6 +141,7 @@ static int ds4424_read_raw(struct iio_dev *indio_dev,
int *val, int *val2, long mask)
{
union ds4424_raw_data raw;
+ struct ds4424_data *data = iio_priv(indio_dev);
int ret;
switch (mask) {
@@ -122,10 +153,19 @@ static int ds4424_read_raw(struct iio_dev *indio_dev,
return ret;
}
raw.bits = *val;
- *val = raw.dx;
+ *val = raw.dx & data->chip_info->result_mask;
if (raw.source_bit == DS4424_SINK_I)
*val = -*val;
return IIO_VAL_INT;
+ case IIO_CHAN_INFO_SCALE:
+ if (!data->has_rfs)
+ return -EINVAL;
+
+ /* SCALE is mA/step: mV / Ohm = mA. */
+ *val = data->chip_info->vref_mv;
+ *val2 = data->rfs_ohms[chan->channel] *
+ data->chip_info->scale_denom;
+ return IIO_VAL_FRACTIONAL;
default:
return -EINVAL;
@@ -136,6 +176,8 @@ static int ds4424_write_raw(struct iio_dev *indio_dev,
struct iio_chan_spec const *chan,
int val, int val2, long mask)
{
+ struct ds4424_data *data = iio_priv(indio_dev);
+ int max_val = data->chip_info->result_mask;
union ds4424_raw_data raw;
if (val2 != 0)
@@ -143,7 +185,12 @@ static int ds4424_write_raw(struct iio_dev *indio_dev,
switch (mask) {
case IIO_CHAN_INFO_RAW:
- if (val <= S8_MIN || val > S8_MAX)
+ /*
+ * The hardware uses sign-magnitude representation (not
+ * two's complement). Therefore, the range is symmetric:
+ * [-max_val, +max_val].
+ */
+ if (val < -max_val || val > max_val)
return -EINVAL;
if (val > 0) {
@@ -173,6 +220,74 @@ static int ds4424_verify_chip(struct iio_dev *indio_dev)
return ret;
}
+static int ds4424_setup_channels(struct i2c_client *client,
+ struct ds4424_data *data,
+ struct iio_dev *indio_dev)
+{
+ struct iio_chan_spec channels[DS4424_MAX_DAC_CHANNELS];
+ size_t channels_size;
+ int i;
+
+ channels_size = indio_dev->num_channels * sizeof(*channels);
+ memcpy(channels, ds4424_channels, channels_size);
+
+ /* Enable scale only when rfs is available. */
+ if (data->has_rfs) {
+ for (i = 0; i < indio_dev->num_channels; i++)
+ channels[i].info_mask_separate |=
+ BIT(IIO_CHAN_INFO_SCALE);
+ }
+
+ indio_dev->channels = devm_kmemdup(&client->dev, channels,
+ channels_size, GFP_KERNEL);
+ if (!indio_dev->channels)
+ return -ENOMEM;
+
+ return 0;
+}
+
+static int ds4424_parse_rfs(struct i2c_client *client,
+ struct ds4424_data *data,
+ struct iio_dev *indio_dev)
+{
+ int count, i, ret;
+
+ if (!device_property_present(&client->dev, "maxim,rfs-ohms")) {
+ dev_info_once(&client->dev, "maxim,rfs-ohms missing, scale not supported\n");
+ return 0;
+ }
+
+ count = device_property_count_u32(&client->dev, "maxim,rfs-ohms");
+ if (count != indio_dev->num_channels) {
+ dev_err(&client->dev,
+ "maxim,rfs-ohms must have %u entries\n",
+ indio_dev->num_channels);
+ return -EINVAL;
+ }
+
+ ret = device_property_read_u32_array(&client->dev,
+ "maxim,rfs-ohms",
+ data->rfs_ohms,
+ indio_dev->num_channels);
+ if (ret) {
+ dev_err(&client->dev,
+ "Failed to read maxim,rfs-ohms property\n");
+ return ret;
+ }
+
+ for (i = 0; i < indio_dev->num_channels; i++) {
+ if (!data->rfs_ohms[i]) {
+ dev_err(&client->dev,
+ "maxim,rfs-ohms entry %d is zero\n",
+ i);
+ return -EINVAL;
+ }
+ }
+
+ data->has_rfs = true;
+ return 0;
+}
+
static int ds4424_suspend(struct device *dev)
{
struct i2c_client *client = to_i2c_client(dev);
@@ -210,7 +325,7 @@ static int ds4424_resume(struct device *dev)
static DEFINE_SIMPLE_DEV_PM_OPS(ds4424_pm_ops, ds4424_suspend, ds4424_resume);
-static const struct iio_info ds4424_info = {
+static const struct iio_info ds4424_iio_info = {
.read_raw = ds4424_read_raw,
.write_raw = ds4424_write_raw,
};
@@ -252,15 +367,20 @@ static int ds4424_probe(struct i2c_client *client)
switch (id->driver_data) {
case ID_DS4402:
indio_dev->num_channels = DS4422_MAX_DAC_CHANNELS;
+ /* See ds4404_info comment above. */
+ data->chip_info = &ds4404_info;
break;
case ID_DS4404:
indio_dev->num_channels = DS4424_MAX_DAC_CHANNELS;
+ data->chip_info = &ds4404_info;
break;
case ID_DS4422:
indio_dev->num_channels = DS4422_MAX_DAC_CHANNELS;
+ data->chip_info = &ds4424_info;
break;
case ID_DS4424:
indio_dev->num_channels = DS4424_MAX_DAC_CHANNELS;
+ data->chip_info = &ds4424_info;
break;
default:
dev_err(&client->dev,
@@ -269,9 +389,16 @@ static int ds4424_probe(struct i2c_client *client)
goto fail;
}
- indio_dev->channels = ds4424_channels;
+ ret = ds4424_parse_rfs(client, data, indio_dev);
+ if (ret)
+ goto fail;
+
+ ret = ds4424_setup_channels(client, data, indio_dev);
+ if (ret)
+ goto fail;
+
indio_dev->modes = INDIO_DIRECT_MODE;
- indio_dev->info = &ds4424_info;
+ indio_dev->info = &ds4424_iio_info;
ret = iio_device_register(indio_dev);
if (ret < 0) {
--
2.47.3On Mon, Jan 19, 2026 at 07:24:21PM +0100, Oleksij Rempel wrote:
> Parse optional maxim,rfs-ohms values to derive the per-channel output
> current scale (mA per step) for the IIO current ABI.
>
> Select per-variant parameters to match the shared register map while
> handling different data widths and full-scale current calculations.
>
> Behavior changes:
> - If maxim,rfs-ohms is present, IIO_CHAN_INFO_SCALE becomes available
> and reports mA/step derived from Rfs.
> - If maxim,rfs-ohms is missing, SCALE is not exposed to keep older DTs
> working without requiring updates.
> - RAW writes are now limited to the representable sign-magnitude range
> of the detected variant to avoid silent truncation (e.g. +/-31 on
> DS440x).
...
> +struct ds4424_chip_info {
> + u8 result_mask;
> + int vref_mv;
> + int scale_denom;
Wondering if `pahole` is fine with the proposed layout.
Otherwise I would move u8 to the end.
> +};
...
> +static const struct ds4424_chip_info ds4424_info = {
> + .result_mask = 0x7F,
GENMASK() ?
(Note, we also have GENMASK_U8() IIRC)
> + .vref_mv = 976,
> + .scale_denom = 16,
> +};
...
> +/* DS4402 is handled like DS4404 (same resolution and scale formula). */
> +static const struct ds4424_chip_info ds4404_info = {
> + .result_mask = 0x1F,
Ditto.
> + .vref_mv = 1230,
> + .scale_denom = 4,
> +};
...
> - if (val <= S8_MIN || val > S8_MAX)
> + /*
> + * The hardware uses sign-magnitude representation (not
> + * two's complement). Therefore, the range is symmetric:
> + * [-max_val, +max_val].
> + */
> + if (val < -max_val || val > max_val)
> return -EINVAL;
Right, cool, but I still think even in the fix it would be good to fix that and
here it will be quite logical and clear change. Maybe even introduce a comment
in the fix-patch and just update limits here.
...
> +static int ds4424_setup_channels(struct i2c_client *client,
> + struct ds4424_data *data,
> + struct iio_dev *indio_dev)
> +{
> + struct iio_chan_spec channels[DS4424_MAX_DAC_CHANNELS];
> + size_t channels_size;
> + int i;
> +
> + channels_size = indio_dev->num_channels * sizeof(*channels);
Sounds like devm_kmemdup_array() to me...
> + memcpy(channels, ds4424_channels, channels_size);
> + /* Enable scale only when rfs is available. */
> + if (data->has_rfs) {
> + for (i = 0; i < indio_dev->num_channels; i++)
> + channels[i].info_mask_separate |=
> + BIT(IIO_CHAN_INFO_SCALE);
> + }
Can be done after kmemdup(), right?
> + indio_dev->channels = devm_kmemdup(&client->dev, channels,
> + channels_size, GFP_KERNEL);
> + if (!indio_dev->channels)
> + return -ENOMEM;
> +
> + return 0;
> +}
...
> +static int ds4424_parse_rfs(struct i2c_client *client,
> + struct ds4424_data *data,
> + struct iio_dev *indio_dev)
> +{
struct device *dev = &client->dev;
> + int count, i, ret;
> +
> + if (!device_property_present(&client->dev, "maxim,rfs-ohms")) {
> + dev_info_once(&client->dev, "maxim,rfs-ohms missing, scale not supported\n");
> + return 0;
> + }
> +
> + count = device_property_count_u32(&client->dev, "maxim,rfs-ohms");
> + if (count != indio_dev->num_channels) {
> + dev_err(&client->dev,
> + "maxim,rfs-ohms must have %u entries\n",
> + indio_dev->num_channels);
> + return -EINVAL;
> + }
> +
> + ret = device_property_read_u32_array(&client->dev,
> + "maxim,rfs-ohms",
> + data->rfs_ohms,
> + indio_dev->num_channels);
> + if (ret) {
> + dev_err(&client->dev,
> + "Failed to read maxim,rfs-ohms property\n");
> + return ret;
> + }
> +
> + for (i = 0; i < indio_dev->num_channels; i++) {
> + if (!data->rfs_ohms[i]) {
> + dev_err(&client->dev,
> + "maxim,rfs-ohms entry %d is zero\n",
> + i);
> + return -EINVAL;
This is only for probe stage, right?
Then
return dev_err_probe();
?
> + }
> + }
> +
> + data->has_rfs = true;
> + return 0;
> +}
--
With Best Regards,
Andy Shevchenko
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