[PATCH v2] iio: adc: mcp3422: use read_avail() for available attributes

[Yuval Saar <thefireking@gmail.com>]

Custom sysfs show functions only expose the sampling frequency and
scale lists to userspace. Use read_avail() and the channel _available
masks so the IIO core creates sampling_frequency_available and
in_voltage_scale_available. Sysfs names and formatted output are
unchanged, and in-kernel IIO consumers can query the lists directly.

Replace magic numbers(chip ids and sample-rate values) with named constants.

Compile tested. checkpatch --strict clean. Sysfs names and available-list
text checked against IIO core formatters. No hardware.

Assisted-by: LLM
Signed-off-by: Yuval Saar <thefireking@gmail.com>
---
 drivers/iio/adc/mcp3422.c | 168 ++++++++++++++++++++------------------
 1 file changed, 90 insertions(+), 78 deletions(-)

diff --git a/drivers/iio/adc/mcp3422.c b/drivers/iio/adc/mcp3422.c
index 36ba00edf..239438dc7 100644
--- a/drivers/iio/adc/mcp3422.c
+++ b/drivers/iio/adc/mcp3422.c
@@ -19,11 +19,9 @@
 #include <linux/i2c.h>
 #include <linux/module.h>
 #include <linux/delay.h>
-#include <linux/sysfs.h>
 #include <linux/unaligned.h>
 
 #include <linux/iio/iio.h>
-#include <linux/iio/sysfs.h>
 
 #define MCP3422_CHANNEL_MASK	GENMASK(6, 5)
 #define MCP3422_SRATE_MASK	GENMASK(3, 2)
@@ -39,6 +37,25 @@
 #define MCP3422_PGA_8	3
 #define MCP3422_CONT_SAMPLING	BIT(4)
 
+/* Sample rates in SPS. MCP3422_SRATE_* above are the config-bit encodings. */
+#define MCP3422_SPS_240	240
+#define MCP3422_SPS_60	60
+#define MCP3422_SPS_15	15
+#define MCP3422_SPS_3	3
+
+/*
+ * i2c_device_id.driver_data / adc->id. MCP3421-4 are 18-bit (3 SPS
+ * available); MCP3425-8 are 16-bit and omit that rate.
+ */
+#define MCP3421_ID		1
+#define MCP3422_ID		2
+#define MCP3423_ID		3
+#define MCP3424_ID		4
+#define MCP3425_ID		5
+#define MCP3426_ID		6
+#define MCP3427_ID		7
+#define MCP3428_ID		8
+
 #define MCP3422_CHAN(_index) \
 	{ \
 		.type = IIO_VOLTAGE, \
@@ -47,27 +64,33 @@
 		.info_mask_separate = BIT(IIO_CHAN_INFO_RAW) \
 				| BIT(IIO_CHAN_INFO_SCALE), \
 		.info_mask_shared_by_type = BIT(IIO_CHAN_INFO_SAMP_FREQ), \
+		.info_mask_shared_by_type_available = \
+				BIT(IIO_CHAN_INFO_SCALE), \
+		.info_mask_shared_by_all_available = \
+				BIT(IIO_CHAN_INFO_SAMP_FREQ), \
 	}
 
-static const int mcp3422_scales[4][4] = {
-	{ 1000000, 500000, 250000, 125000 },
-	{ 250000,  125000, 62500,  31250  },
-	{ 62500,   31250,  15625,  7812   },
-	{ 15625,   7812,   3906,   1953   } };
+/* IIO_VAL_INT_PLUS_NANO lists: { integer, nano } per PGA gain. */
+static const int mcp3422_scale_avail[][8] = {
+	[MCP3422_SRATE_240] = { 0, 1000000, 0, 500000, 0, 250000, 0, 125000 },
+	[MCP3422_SRATE_60]  = { 0, 250000,  0, 125000, 0, 62500,  0, 31250  },
+	[MCP3422_SRATE_15]  = { 0, 62500,   0, 31250,  0, 15625,  0, 7812   },
+	[MCP3422_SRATE_3]   = { 0, 15625,   0, 7812,   0, 3906,   0, 1953   },
+};
 
 /* Constant msleep times for data acquisitions */
-static const int mcp3422_read_times[4] = {
-	[MCP3422_SRATE_240] = 1000 / 240,
-	[MCP3422_SRATE_60] = 1000 / 60,
-	[MCP3422_SRATE_15] = 1000 / 15,
-	[MCP3422_SRATE_3] = 1000 / 3 };
-
-/* sample rates to integer conversion table */
-static const int mcp3422_sample_rates[4] = {
-	[MCP3422_SRATE_240] = 240,
-	[MCP3422_SRATE_60] = 60,
-	[MCP3422_SRATE_15] = 15,
-	[MCP3422_SRATE_3] = 3 };
+static const int mcp3422_read_times[] = {
+	[MCP3422_SRATE_240] = 1000 / MCP3422_SPS_240,
+	[MCP3422_SRATE_60] = 1000 / MCP3422_SPS_60,
+	[MCP3422_SRATE_15] = 1000 / MCP3422_SPS_15,
+	[MCP3422_SRATE_3] = 1000 / MCP3422_SPS_3 };
+
+/* sample rates to integer conversion table; 3 SPS is last and 18-bit only */
+static const int mcp3422_sample_rates[] = {
+	[MCP3422_SRATE_240] = MCP3422_SPS_240,
+	[MCP3422_SRATE_60] = MCP3422_SPS_60,
+	[MCP3422_SRATE_15] = MCP3422_SPS_15,
+	[MCP3422_SRATE_3] = MCP3422_SPS_3 };
 
 /* sample rates to sign extension table */
 static const int mcp3422_sign_extend[4] = {
@@ -169,7 +192,7 @@ static int mcp3422_read_raw(struct iio_dev *iio,
 	case IIO_CHAN_INFO_SCALE:
 
 		*val1 = 0;
-		*val2 = mcp3422_scales[sample_rate][pga];
+		*val2 = mcp3422_scale_avail[sample_rate][2 * pga + 1];
 		return IIO_VAL_INT_PLUS_NANO;
 
 	case IIO_CHAN_INFO_SAMP_FREQ:
@@ -199,8 +222,8 @@ static int mcp3422_write_raw(struct iio_dev *iio,
 		if (val1 != 0)
 			return -EINVAL;
 
-		for (i = 0; i < ARRAY_SIZE(mcp3422_scales[0]); i++) {
-			if (val2 == mcp3422_scales[sample_rate][i]) {
+		for (i = 0; i < ARRAY_SIZE(mcp3422_scale_avail[0]) / 2; i++) {
+			if (val2 == mcp3422_scale_avail[sample_rate][2 * i + 1]) {
 				adc->pga[req_channel] = i;
 
 				FIELD_MODIFY(MCP3422_CHANNEL_MASK, &config, req_channel);
@@ -213,17 +236,17 @@ static int mcp3422_write_raw(struct iio_dev *iio,
 
 	case IIO_CHAN_INFO_SAMP_FREQ:
 		switch (val1) {
-		case 240:
+		case MCP3422_SPS_240:
 			temp = MCP3422_SRATE_240;
 			break;
-		case 60:
+		case MCP3422_SPS_60:
 			temp = MCP3422_SRATE_60;
 			break;
-		case 15:
+		case MCP3422_SPS_15:
 			temp = MCP3422_SRATE_15;
 			break;
-		case 3:
-			if (adc->id > 4)
+		case MCP3422_SPS_3:
+			if (adc->id > MCP3424_ID)
 				return -EINVAL;
 			temp = MCP3422_SRATE_3;
 			break;
@@ -256,45 +279,34 @@ static int mcp3422_write_raw_get_fmt(struct iio_dev *indio_dev,
 	}
 }
 
-static ssize_t mcp3422_show_samp_freqs(struct device *dev,
-		struct device_attribute *attr, char *buf)
-{
-	struct mcp3422 *adc = iio_priv(dev_to_iio_dev(dev));
-
-	if (adc->id > 4)
-		return sprintf(buf, "240 60 15\n");
-
-	return sprintf(buf, "240 60 15 3\n");
-}
-
-static ssize_t mcp3422_show_scales(struct device *dev,
-		struct device_attribute *attr, char *buf)
+static int mcp3422_read_avail(struct iio_dev *indio_dev,
+			      struct iio_chan_spec const *chan,
+			      const int **vals, int *type, int *length,
+			      long mask)
 {
-	struct mcp3422 *adc = iio_priv(dev_to_iio_dev(dev));
+	struct mcp3422 *adc = iio_priv(indio_dev);
 	u8 sample_rate = FIELD_GET(MCP3422_SRATE_MASK, adc->config);
 
-	return sprintf(buf, "0.%09u 0.%09u 0.%09u 0.%09u\n",
-		mcp3422_scales[sample_rate][0],
-		mcp3422_scales[sample_rate][1],
-		mcp3422_scales[sample_rate][2],
-		mcp3422_scales[sample_rate][3]);
+	switch (mask) {
+	case IIO_CHAN_INFO_SCALE:
+		*vals = mcp3422_scale_avail[sample_rate];
+		*type = IIO_VAL_INT_PLUS_NANO;
+		*length = ARRAY_SIZE(mcp3422_scale_avail[0]);
+		return IIO_AVAIL_LIST;
+	case IIO_CHAN_INFO_SAMP_FREQ:
+		*vals = mcp3422_sample_rates;
+		*type = IIO_VAL_INT;
+		if (adc->id <= MCP3424_ID)
+			*length = ARRAY_SIZE(mcp3422_sample_rates);
+		else
+			/* 16-bit parts: drop trailing 3 SPS entry */
+			*length = ARRAY_SIZE(mcp3422_sample_rates) - 1;
+		return IIO_AVAIL_LIST;
+	default:
+		return -EINVAL;
+	}
 }
 
-static IIO_DEVICE_ATTR(sampling_frequency_available, S_IRUGO,
-		mcp3422_show_samp_freqs, NULL, 0);
-static IIO_DEVICE_ATTR(in_voltage_scale_available, S_IRUGO,
-		mcp3422_show_scales, NULL, 0);
-
-static struct attribute *mcp3422_attributes[] = {
-	&iio_dev_attr_sampling_frequency_available.dev_attr.attr,
-	&iio_dev_attr_in_voltage_scale_available.dev_attr.attr,
-	NULL,
-};
-
-static const struct attribute_group mcp3422_attribute_group = {
-	.attrs = mcp3422_attributes,
-};
-
 static const struct iio_chan_spec mcp3421_channels[] = {
 	MCP3422_CHAN(0),
 };
@@ -313,9 +325,9 @@ static const struct iio_chan_spec mcp3424_channels[] = {
 
 static const struct iio_info mcp3422_info = {
 	.read_raw = mcp3422_read_raw,
+	.read_avail = mcp3422_read_avail,
 	.write_raw = mcp3422_write_raw,
 	.write_raw_get_fmt = mcp3422_write_raw_get_fmt,
-	.attrs = &mcp3422_attribute_group,
 };
 
 static int mcp3422_probe(struct i2c_client *client)
@@ -344,20 +356,20 @@ static int mcp3422_probe(struct i2c_client *client)
 	indio_dev->info = &mcp3422_info;
 
 	switch (adc->id) {
-	case 1:
-	case 5:
+	case MCP3421_ID:
+	case MCP3425_ID:
 		indio_dev->channels = mcp3421_channels;
 		indio_dev->num_channels = ARRAY_SIZE(mcp3421_channels);
 		break;
-	case 2:
-	case 3:
-	case 6:
-	case 7:
+	case MCP3422_ID:
+	case MCP3423_ID:
+	case MCP3426_ID:
+	case MCP3427_ID:
 		indio_dev->channels = mcp3422_channels;
 		indio_dev->num_channels = ARRAY_SIZE(mcp3422_channels);
 		break;
-	case 4:
-	case 8:
+	case MCP3424_ID:
+	case MCP3428_ID:
 		indio_dev->channels = mcp3424_channels;
 		indio_dev->num_channels = ARRAY_SIZE(mcp3424_channels);
 		break;
@@ -382,14 +394,14 @@ static int mcp3422_probe(struct i2c_client *client)
 }
 
 static const struct i2c_device_id mcp3422_id[] = {
-	{ .name = "mcp3421", .driver_data = 1 },
-	{ .name = "mcp3422", .driver_data = 2 },
-	{ .name = "mcp3423", .driver_data = 3 },
-	{ .name = "mcp3424", .driver_data = 4 },
-	{ .name = "mcp3425", .driver_data = 5 },
-	{ .name = "mcp3426", .driver_data = 6 },
-	{ .name = "mcp3427", .driver_data = 7 },
-	{ .name = "mcp3428", .driver_data = 8 },
+	{ .name = "mcp3421", .driver_data = MCP3421_ID },
+	{ .name = "mcp3422", .driver_data = MCP3422_ID },
+	{ .name = "mcp3423", .driver_data = MCP3423_ID },
+	{ .name = "mcp3424", .driver_data = MCP3424_ID },
+	{ .name = "mcp3425", .driver_data = MCP3425_ID },
+	{ .name = "mcp3426", .driver_data = MCP3426_ID },
+	{ .name = "mcp3427", .driver_data = MCP3427_ID },
+	{ .name = "mcp3428", .driver_data = MCP3428_ID },
 	{ }
 };
 MODULE_DEVICE_TABLE(i2c, mcp3422_id);

base-commit: 69fa76f0af3414cc189c3b0b807cb59e327ecc00
-- 
2.43.0

---
v2:
- Use read_avail() instead of custom sysfs show functions (Jonathan)
- Use a known identity on Signed-off-by (Maxwell, Jonathan)
- Replace magic numbers (chip ids and sample rates) with named constants
v1: https://lore.kernel.org/linux-iio/20260919195507.94130-1-thefireking@gmail.com/