linux-kernel - [PATCH v2] iio: ad5933: Correct settling cycles encoding per datasheet

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Message-ID: <20250418181025.637710-1-gshahrouzi@gmail.com>
Date: Fri, 18 Apr 2025 14:10:25 -0400
From: Gabriel Shahrouzi <gshahrouzi@...il.com>
To: gregkh@...uxfoundation.org,
	jic23@...nel.org,
	lars@...afoo.de,
	linux-iio@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	linux-staging@...ts.linux.dev,
	Michael.Hennerich@...log.com
Cc: gshahrouzi@...il.com,
	skhan@...uxfoundation.org,
	linux-kernel-mentees@...ts.linux.dev,
	stable@...r.kernel.org
Subject: [PATCH v2] iio: ad5933: Correct settling cycles encoding per datasheet

Implement the settling cycles encoding as specified in the AD5933
datasheet, Table 13 ("Number of Settling Times Cycles Register"). The
previous logic did not correctly translate the user-requested effective
cycle count into the required 9-bit base + 2-bit multiplier format
(D10..D0) for values exceeding 511.

Clamp the user input for out_altvoltage0_settling_cycles to the
maximum effective value of 2044 cycles (511 * 4x multiplier).

Fixes: f94aa354d676 ("iio: impedance-analyzer: New driver for AD5933/4 Impedance Converter, Network Analyzer")
Cc: stable@...r.kernel.org
Signed-off-by: Gabriel Shahrouzi <gshahrouzi@...il.com>
---
Changes in v2:
	- Fix spacing in comment around '+'.
	- Define mask and values for settling cycle multipliers.
---
 .../staging/iio/impedance-analyzer/ad5933.c   | 23 +++++++++++++------
 1 file changed, 16 insertions(+), 7 deletions(-)

diff --git a/drivers/staging/iio/impedance-analyzer/ad5933.c b/drivers/staging/iio/impedance-analyzer/ad5933.c
index d5544fc2fe989..3c301a8ebd2ab 100644
--- a/drivers/staging/iio/impedance-analyzer/ad5933.c
+++ b/drivers/staging/iio/impedance-analyzer/ad5933.c
@@ -28,7 +28,7 @@
 #define AD5933_REG_FREQ_START		0x82	/* R/W, 3 bytes */
 #define AD5933_REG_FREQ_INC		0x85	/* R/W, 3 bytes */
 #define AD5933_REG_INC_NUM		0x88	/* R/W, 2 bytes, 9 bit */
-#define AD5933_REG_SETTLING_CYCLES	0x8A	/* R/W, 2 bytes */
+#define AD5933_REG_SETTLING_CYCLES	0x8A	/* R/W, 2 bytes, 11 + 2 bit */
 #define AD5933_REG_STATUS		0x8F	/* R, 1 byte */
 #define AD5933_REG_TEMP_DATA		0x92	/* R, 2 bytes*/
 #define AD5933_REG_REAL_DATA		0x94	/* R, 2 bytes*/
@@ -71,6 +71,8 @@
 #define AD5933_INT_OSC_FREQ_Hz		16776000
 #define AD5933_MAX_OUTPUT_FREQ_Hz	100000
 #define AD5933_MAX_RETRIES		100
+#define AD5933_MAX_FREQ_POINTS		511
+#define AD5933_MAX_SETTLING_CYCLES	2044 /* 511 * 4 */
 
 #define AD5933_OUT_RANGE		1
 #define AD5933_OUT_RANGE_AVAIL		2
@@ -82,6 +84,12 @@
 #define AD5933_POLL_TIME_ms		10
 #define AD5933_INIT_EXCITATION_TIME_ms	100
 
+/* Settling cycles multiplier bits D10, D9 */
+#define AD5933_SETTLE_MUL_MASK		(BIT(10) | BIT(9))
+#define AD5933_SETTLE_MUL_1X		0
+#define AD5933_SETTLE_MUL_2X		BIT(9)
+#define AD5933_SETTLE_MUL_4X		(BIT(10) | BIT(9))
+
 struct ad5933_state {
 	struct i2c_client		*client;
 	struct clk			*mclk;
@@ -411,14 +419,15 @@ static ssize_t ad5933_store(struct device *dev,
 		ret = ad5933_cmd(st, 0);
 		break;
 	case AD5933_OUT_SETTLING_CYCLES:
-		val = clamp(val, (u16)0, (u16)0x7FF);
+		val = clamp(val, (u16)0, (u16)AD5933_MAX_SETTLING_CYCLES);
 		st->settling_cycles = val;
 
-		/* 2x, 4x handling, see datasheet */
+		/* Encode value for register: D10..D0 */
+		/* Datasheet Table 13: If cycles > 1022 -> val/4, set bits D10=1, D9=1 */
 		if (val > 1022)
-			val = (val >> 2) | (3 << 9);
-		else if (val > 511)
-			val = (val >> 1) | BIT(9);
+			val = (val >> 2) | AD5933_SETTLE_MUL_4X;
+		else if (val > 511) /* Datasheet: If cycles > 511 -> val/2, set bit D9=1 */
+			val = (val >> 1) | AD5933_SETTLE_MUL_2X;
 
 		dat = cpu_to_be16(val);
 		ret = ad5933_i2c_write(st->client,
@@ -426,7 +435,7 @@ static ssize_t ad5933_store(struct device *dev,
 				       2, (u8 *)&dat);
 		break;
 	case AD5933_FREQ_POINTS:
-		val = clamp(val, (u16)0, (u16)511);
+		val = clamp(val, (u16)0, (u16)AD5933_MAX_FREQ_POINTS);
 		st->freq_points = val;
 
 		dat = cpu_to_be16(val);
-- 
2.43.0