[PATCH v2 0/2] iio: proximity: sx9310/sx9360: reject out-of-range hardware gain values

[PATCH v2 0/2] iio: proximity: sx9310/sx9360: reject out-of-range hardware gain values

[Arnav Kapoor]

sx9310_write_gain() and sx9360_write_gain() squeeze ilog2() of any
integer into the register field. Values that don't fit wrap around,
and 0 and negative values turn into the maximum code, while the write
reports success. Reject those. One patch per driver, as the Fixes tags
differ.

Changes in v2:
- Keep rounding values between the supported gains down, instead of
  rejecting them, so the ABI doesn't change (Jonathan)
- Only reject values <= 0 and values that don't fit: FIELD_FIT() for
  sx9310 (Jonathan); sx9360 checks against the gain of 8 code, as its
  3-bit field also holds codes 4 to 7, which the driver doesn't support

v1: https://lore.kernel.org/all/20261107111710.442318-1-kapoorarnav43@gmail.com/

Compile-tested only (W=1); I don't have SX9310 or SX9360 hardware.

Arnav Kapoor (2):
  iio: proximity: sx9310: reject out-of-range hardware gain values
  iio: proximity: sx9360: reject out-of-range hardware gain values

 drivers/iio/proximity/sx9310.c | 7 +++++++
 drivers/iio/proximity/sx9360.c | 7 +++++++
 2 files changed, 14 insertions(+)


base-commit: 340d44bdf9db0f095f99845b5ad8628781d79b6f
-- 
2.53.0

[PATCH v2 1/2] iio: proximity: sx9310: reject out-of-range hardware gain values

[Arnav Kapoor]

sx9310_write_gain() passes the value from userspace to ilog2() and then
FIELD_PREP() into a 2-bit gain field without checking it, so some
values silently program a gain unrelated to the one requested, and the
write still reports success:

  - 16 and larger wrap around in the 2-bit field, e.g. 16 sets a gain
    of 1 and 32 a gain of 2;
  - 0 and negative values set the maximum gain of 8, because ilog2(0)
    is -1 and a negative int becomes a large unsigned value.

Return -EINVAL for values <= 0 and for values whose ilog2() does not
fit in the gain field. Values between the supported gains of 1, 2, 4
and 8 are still rounded down, as before, and the gain read back
reflects what was applied.

Fixes: 227c83faa2f8 ("iio: sx9310: Support hardware gain factor")
Signed-off-by: Arnav Kapoor <kapoorarnav43@gmail.com>
---
 drivers/iio/proximity/sx9310.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/drivers/iio/proximity/sx9310.c b/drivers/iio/proximity/sx9310.c
index 2585b9c6fb69..9177d6d4a0a1 100644
--- a/drivers/iio/proximity/sx9310.c
+++ b/drivers/iio/proximity/sx9310.c
@@ -665,16 +665,23 @@ static int sx9310_write_gain(struct sx_common_data *data,
 {
 	unsigned int gain, mask;
 
+	if (val <= 0)
+		return -EINVAL;
+
 	gain = ilog2(val);
 
 	switch (chan->channel) {
 	case 0:
 	case 3:
+		if (!FIELD_FIT(SX9310_REG_PROX_CTRL3_GAIN0_MASK, gain))
+			return -EINVAL;
 		mask = SX9310_REG_PROX_CTRL3_GAIN0_MASK;
 		gain = FIELD_PREP(SX9310_REG_PROX_CTRL3_GAIN0_MASK, gain);
 		break;
 	case 1:
 	case 2:
+		if (!FIELD_FIT(SX9310_REG_PROX_CTRL3_GAIN12_MASK, gain))
+			return -EINVAL;
 		mask = SX9310_REG_PROX_CTRL3_GAIN12_MASK;
 		gain = FIELD_PREP(SX9310_REG_PROX_CTRL3_GAIN12_MASK, gain);
 		break;
-- 
2.53.0

[PATCH v2 2/2] iio: proximity: sx9360: reject out-of-range hardware gain values

[Arnav Kapoor]

sx9360_write_gain() passes the value from userspace to ilog2() and then
FIELD_PREP() into the 3-bit PROX_CTRL0 gain field without checking it,
so some values silently program a gain unrelated to the one requested,
and the write still reports success:

  - 16 to 255 write gain codes 4 to 7, which the driver does not
    advertise, and the next read reports gains of 16 to 128;
  - 256 and larger wrap around in the field, e.g. 256 sets a gain of 1;
  - 0 and negative values write code 7 (read back as 128), because
    ilog2(0) is -1 and a negative int becomes a large unsigned value.

Return -EINVAL for values <= 0 and for values above the gain of 8 code.
FIELD_FIT() is not enough here, as the field also holds codes 4 to 7,
which the driver doesn't support. Values between the supported gains
of 1, 2, 4 and 8 are still rounded down, as before.

Fixes: 1cdb4c47f7f5 ("iio:proximity:sx9360: Add sx9360 support")
Signed-off-by: Arnav Kapoor <kapoorarnav43@gmail.com>
---
 drivers/iio/proximity/sx9360.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/drivers/iio/proximity/sx9360.c b/drivers/iio/proximity/sx9360.c
index 2a9b37df8f62..ede20dfcdd80 100644
--- a/drivers/iio/proximity/sx9360.c
+++ b/drivers/iio/proximity/sx9360.c
@@ -68,6 +68,7 @@
 #define SX9360_REG_PROX_CTRL0_PHM	0x41
 #define SX9360_REG_PROX_CTRL0_GAIN_MASK	GENMASK(5, 3)
 #define SX9360_REG_PROX_CTRL0_GAIN_1		0x80
+#define SX9360_REG_PROX_CTRL0_GAIN_8		0x3
 #define SX9360_REG_PROX_CTRL0_RAWFILT_MASK	GENMASK(2, 0)
 #define SX9360_REG_PROX_CTRL0_RAWFILT_1P50	0x01
 #define SX9360_REG_PROX_CTRL1		0x42
@@ -625,7 +626,13 @@ static int sx9360_write_gain(struct sx_common_data *data,
 {
 	unsigned int gain, reg;
 
+	if (val <= 0)
+		return -EINVAL;
+
 	gain = ilog2(val);
+	if (gain > SX9360_REG_PROX_CTRL0_GAIN_8)
+		return -EINVAL;
+
 	reg = SX9360_REG_PROX_CTRL0_PHR + chan->channel;
 	gain = FIELD_PREP(SX9360_REG_PROX_CTRL0_GAIN_MASK, gain);
 
-- 
2.53.0

Re: [PATCH v2 0/2] iio: proximity: sx9310/sx9360: reject out-of-range hardware gain values

[Andy Shevchenko]

On Mon, Nov 09, 2026 at 10:21:51PM +0530, Arnav Kapoor wrote:
> sx9310_write_gain() and sx9360_write_gain() squeeze ilog2() of any
> integer into the register field. Values that don't fit wrap around,
> and 0 and negative values turn into the maximum code, while the write
> reports success. Reject those. One patch per driver, as the Fixes tags
> differ.

I would change the error code to -ERANGE which is clearly states that the range
for numbers is wrong (like mathematically). -EINVAL is way too far overloaded
with semantics.

-- 
With Best Regards,
Andy Shevchenko