[PATCH v2] iio: proximity: sx9360: fix sampling frequency write and available range

[Arnav Kapoor <kapoorarnav43@gmail.com>]

GNRL_CTRL1/2 hold the scan period in units of 8192 / FOSC, but
sx9360_set_samp_freq() computes freq * 8192 / FOSC and mis-scales val2,
which is in micro units. Any integer frequency then programs a period
of 0, and fractional parts above ~0.26 Hz overflow the int, writing
0x10 to GNRL_CTRL1 outside the SCANPERIOD field.

Compute FOSC / (freq * 8192), rounded to the closest value, and reject
frequencies outside the 1..2047 period range.

The available range doesn't match the limits in the comments next to it
either: 4 MHz / 8192 is 488.28125 Hz, not 448.28125 Hz,
4 MHz / (8192 * 2047) is 0.238535 Hz, and (max - min) / 2047 is
0.238419 Hz. Use those values.

Fixes: 1cdb4c47f7f5 ("iio:proximity:sx9360: Add sx9360 support")
Signed-off-by: Arnav Kapoor <kapoorarnav43@gmail.com>
---
Changes in v2:
- Rename period to period_ticks and say in the comment what a tick is (Andy)
- Rename freq_uhz to freq_uHz and use MICROHZ_PER_HZ instead of MICRO (Andy)
- Add a blank line before guard() (Andy)

Converting sx9360_samp_freq_interval[] to a plain int array is left for
a separate cleanup.

Compile-tested only (W=1); I don't have SX9360 hardware.

v1: https://lore.kernel.org/all/20261024180149.144609-1-kapoorarnav43@gmail.com/

 drivers/iio/proximity/sx9360.c | 29 +++++++++++++++++++++++------
 1 file changed, 23 insertions(+), 6 deletions(-)

diff --git a/drivers/iio/proximity/sx9360.c b/drivers/iio/proximity/sx9360.c
index ed83d809ecf5..2a9b37df8f62 100644
--- a/drivers/iio/proximity/sx9360.c
+++ b/drivers/iio/proximity/sx9360.c
@@ -14,10 +14,12 @@
 #include <linux/interrupt.h>
 #include <linux/kernel.h>
 #include <linux/log2.h>
+#include <linux/math64.h>
 #include <linux/module.h>
 #include <linux/pm.h>
 #include <linux/property.h>
 #include <linux/regmap.h>
+#include <linux/units.h>
 
 #include <linux/iio/iio.h>
 
@@ -43,6 +45,7 @@
 #define SX9360_REG_GNRL_CTRL1_SCANPERIOD_MASK GENMASK(2, 0)
 #define SX9360_REG_GNRL_CTRL2		0x12
 #define SX9360_REG_GNRL_CTRL2_PERIOD_102MS	0x32
+#define SX9360_REG_GNRL_SCANPERIOD_MAX		GENMASK(10, 0)
 #define SX9360_REG_GNRL_REG_2_PERIOD_MS(_r)	\
 	(((_r) * 8192) / (SX9360_FOSC_HZ / 1000))
 #define SX9360_REG_GNRL_FREQ_2_REG(_f)  (((_f) * 8192) / SX9360_FOSC_HZ)
@@ -182,9 +185,9 @@ static const struct {
 	int val;
 	int val2;
 } sx9360_samp_freq_interval[] = {
-	{ 0, 281250 },  /* 4MHz / (8192 * 2047) */
-	{ 0, 281250 },
-	{ 448, 281250 },  /* 4MHz / 8192 */
+	{ 0, 238535 },  /* 4MHz / (8192 * 2047) */
+	{ 0, 238419 },
+	{ 488, 281250 },  /* 4MHz / 8192 */
 };
 
 static const struct regmap_range sx9360_writable_reg_ranges[] = {
@@ -383,11 +386,25 @@ static int sx9360_read_avail(struct iio_dev *indio_dev,
 static int sx9360_set_samp_freq(struct sx_common_data *data,
 				int val, int val2)
 {
-	int reg;
+	unsigned int period_ticks;
+	u64 freq_uHz;
 	__be16 buf;
 
-	reg = val * 8192 / SX9360_FOSC_HZ + val2 * 8192 / (SX9360_FOSC_MHZ);
-	buf = cpu_to_be16(reg);
+	if (val < 0 || val2 < 0)
+		return -EINVAL;
+
+	freq_uHz = (u64)val * MICROHZ_PER_HZ + val2;
+	if (!freq_uHz)
+		return -EINVAL;
+
+	/* The register holds the scan period in ticks of 8192 FOSC cycles. */
+	period_ticks = DIV64_U64_ROUND_CLOSEST((u64)SX9360_FOSC_HZ * MICROHZ_PER_HZ,
+					       freq_uHz * 8192);
+	if (!period_ticks || period_ticks > SX9360_REG_GNRL_SCANPERIOD_MAX)
+		return -EINVAL;
+
+	buf = cpu_to_be16(period_ticks);
+
 	guard(mutex)(&data->mutex);
 
 	return regmap_bulk_write(data->regmap, SX9360_REG_GNRL_CTRL1, &buf,

base-commit: 2ef6f5c4ee56e90c237c5f7687f09e635f7d30a9
-- 
2.53.0