[PATCH] iio: adc: mcp320x: refactor driver to use bitfield API

Gustavo Pagnotta Faria
2026-04-20T21:50:38Z

Update the mcp320x driver to use the standard Linux bitfield
API (<linux/bitfield.h>) instead of manual bitwise shifts and masks.

This replaces the hardcoded shift operations in the TX data
preparation (mcp320x_channel_to_tx_data) with FIELD_PREP()
and replaces the manual masking in the RX data extraction
(mcp320x_adc_conversion) with FIELD_GET(). Explicit masks
using GENMASK() and BIT() were also introduced for both transmit
configurations and receive extractions.

Signed-off-by: Gustavo Pagnotta Faria <gustavo.pagnotta@ime.usp.br>
Co-developed-by: Eduardo Augusto <eduardoaugustoabc@ime.usp.br>
Signed-off-by: Eduardo Augusto <eduardoaugustoabc@ime.usp.br>
Co-developed-by: Christian Barry <christian.barry@ime.usp.br>
Signed-off-by: Christian Barry <christian.barry@ime.usp.br>
---
drivers/iio/adc/mcp320x.c | 58 +++++++++++++++++++++++++++------------
1 file changed, 41 insertions(+), 17 deletions(-)

diff --git a/drivers/iio/adc/mcp320x.c b/drivers/iio/adc/mcp320x.c
index 57cff3772ebe..b7523e5ea903 100644
--- a/drivers/iio/adc/mcp320x.c
+++ b/drivers/iio/adc/mcp320x.c
@@ -44,6 +44,29 @@
#include <linux/mod_devicetable.h>
#include <linux/iio/iio.h>
#include <linux/regulator/consumer.h>
+#include <linux/bitfield.h>
+#include <linux/bits.h>
+
+/* MCP3x02/04/08 Tx Data configuration */
+#define MCP3X02_START_BIT BIT(4)
+#define MCP3X02_SGL_DIFF BIT(3)
+#define MCP3X02_CH_MASK BIT(2)
+
+#define MCP3X04_08_START_BIT BIT(6)
+#define MCP3X04_08_SGL_DIFF BIT(5)
+#define MCP3X04_08_CH_MASK GENMASK(4, 2)
+
+/* MCP Rx Data extraction masks */
+#define MCP3001_DATA_MASK GENMASK(12, 3)
+#define MCP300X_DATA_MASK GENMASK(15, 6)
+#define MCP3201_DATA_MASK GENMASK(12, 1)
+#define MCP320X_DATA_MASK GENMASK(15, 4)
+#define MCP3301_DATA_MASK GENMASK(12, 0)
+
+/* MCP355X Data and Status bits */
+#define MCP355X_DATA_MASK GENMASK(31, 8)
+#define MCP355X_SGN BIT(23)
+#define MCP355X_OVR BIT(22)

enum {
mcp3001,
@@ -99,19 +122,19 @@ struct mcp320x {
static int mcp320x_channel_to_tx_data(int device_index,
const unsigned int channel, bool differential)
{
- int start_bit = 1;
-
switch (device_index) {
case mcp3002:
case mcp3202:
- return ((start_bit << 4) | (!differential << 3) |
- (channel << 2));
+ return FIELD_PREP(MCP3X02_START_BIT, 1) |
+ FIELD_PREP(MCP3X02_SGL_DIFF, !differential) |
+ FIELD_PREP(MCP3X02_CH_MASK, channel);
case mcp3004:
case mcp3204:
case mcp3008:
case mcp3208:
- return ((start_bit << 6) | (!differential << 5) |
- (channel << 2));
+ return FIELD_PREP(MCP3X04_08_START_BIT, 1) |
+ FIELD_PREP(MCP3X04_08_SGL_DIFF, !differential) |
+ FIELD_PREP(MCP3X04_08_CH_MASK, channel);
default:
return -EINVAL;
}
@@ -140,26 +163,27 @@ static int mcp320x_adc_conversion(struct mcp320x *adc, u8 channel,
if (ret < 0)
return ret;

+ u16 raw16 = be16_to_cpup((__be16 *)adc->rx_buf);
+
switch (device_index) {
case mcp3001:
- *val = (adc->rx_buf[0] << 5 | adc->rx_buf[1] >> 3);
+ *val = FIELD_GET(MCP3001_DATA_MASK, raw16);
return 0;
case mcp3002:
case mcp3004:
case mcp3008:
- *val = (adc->rx_buf[0] << 2 | adc->rx_buf[1] >> 6);
+ *val = FIELD_GET(MCP300X_DATA_MASK, raw16);
return 0;
case mcp3201:
- *val = (adc->rx_buf[0] << 7 | adc->rx_buf[1] >> 1);
+ *val = FIELD_GET(MCP3201_DATA_MASK, raw16);
return 0;
case mcp3202:
case mcp3204:
case mcp3208:
- *val = (adc->rx_buf[0] << 4 | adc->rx_buf[1] >> 4);
+ *val = FIELD_GET(MCP320X_DATA_MASK, raw16);
return 0;
case mcp3301:
- *val = sign_extend32((adc->rx_buf[0] & 0x1f) << 8
- | adc->rx_buf[1], 12);
+ *val = sign_extend32(FIELD_GET(MCP3301_DATA_MASK, raw16), 12);
return 0;
case mcp3550_50:
case mcp3550_60:
@@ -170,17 +194,17 @@ static int mcp320x_adc_conversion(struct mcp320x *adc, u8 channel,
if (!(adc->spi->mode & SPI_CPOL))
raw <<= 1; /* strip Data Ready bit in SPI mode 0,0 */

+ raw = FIELD_GET(MCP355X_DATA_MASK, raw);
/*
* If the input is within -vref and vref, bit 21 is the sign.
* Up to 12% overrange or underrange are allowed, in which case
* bit 23 is the sign and bit 0 to 21 is the value.
*/
- raw >>= 8;
- if (raw & BIT(22) && raw & BIT(23))
+ if ((raw & MCP355X_OVR) && (raw & MCP355X_SGN))
return -EIO; /* cannot have overrange AND underrange */
- else if (raw & BIT(22))
- raw &= ~BIT(22); /* overrange */
- else if (raw & BIT(23) || raw & BIT(21))
+ else if (raw & MCP355X_OVR)
+ raw &= MCP355X_OVR; /* overrange */
+ else if ((raw & MCP355X_SGN) || (raw & BIT(21)))
raw |= GENMASK(31, 22); /* underrange or negative */

*val = (s32)raw;
--
2.43.0