[PATCH v7 1/2] iio: sx9310: Fix access to variable DT array

[Gwendal Grignou <gwendal@chromium.org>]

With the current code, we want to read 4 entries from DT array
"semtech,combined-sensors". If there are less, we silently fail as
of_property_read_u32_array() returns -EOVERFLOW.

First count the number of entries and if between 1 and 4, collect the
content of the array.

Fixes: 5b19ca2c78a0 ("iio: sx9310: Set various settings from DT")
Signed-off-by: Gwendal Grignou <gwendal@chromium.org>
Reviewed-by: Andy Shevchenko <andy.shevchenko@gmail.com>
---
 No changes in v7.

 Changes in v6:
 Fix error in of_property_count_elems_of_size() argumnent:
 Used ARRAY_SIZE(combined) [4] instead of sizeof(u32).

 Changes in v5:
 new, split fixes from changes needed for ACPI support.

 drivers/iio/proximity/sx9310.c | 40 ++++++++++++++++++++++++----------
 1 file changed, 28 insertions(+), 12 deletions(-)

diff --git a/drivers/iio/proximity/sx9310.c b/drivers/iio/proximity/sx9310.c
index 394c2afe0f233..289c76bb3b024 100644
--- a/drivers/iio/proximity/sx9310.c
+++ b/drivers/iio/proximity/sx9310.c
@@ -1213,17 +1213,17 @@ static int sx9310_init_compensation(struct iio_dev *indio_dev)
 }
 
 static const struct sx9310_reg_default *
-sx9310_get_default_reg(struct sx9310_data *data, int i,
+sx9310_get_default_reg(struct sx9310_data *data, int idx,
 		       struct sx9310_reg_default *reg_def)
 {
-	int ret;
 	const struct device_node *np = data->client->dev.of_node;
-	u32 combined[SX9310_NUM_CHANNELS] = { 4, 4, 4, 4 };
+	u32 combined[SX9310_NUM_CHANNELS];
+	u32 start = 0, raw = 0, pos = 0;
 	unsigned long comb_mask = 0;
+	int ret, i, count;
 	const char *res;
-	u32 start = 0, raw = 0, pos = 0;
 
-	memcpy(reg_def, &sx9310_default_regs[i], sizeof(*reg_def));
+	memcpy(reg_def, &sx9310_default_regs[idx], sizeof(*reg_def));
 	if (!np)
 		return reg_def;
 
@@ -1234,15 +1234,31 @@ sx9310_get_default_reg(struct sx9310_data *data, int i,
 			reg_def->def |= SX9310_REG_PROX_CTRL2_SHIELDEN_GROUND;
 		}
 
-		reg_def->def &= ~SX9310_REG_PROX_CTRL2_COMBMODE_MASK;
-		of_property_read_u32_array(np, "semtech,combined-sensors",
-					   combined, ARRAY_SIZE(combined));
-		for (i = 0; i < ARRAY_SIZE(combined); i++) {
-			if (combined[i] <= SX9310_NUM_CHANNELS)
-				comb_mask |= BIT(combined[i]);
+		count = of_property_count_elems_of_size(np, "semtech,combined-sensors",
+							sizeof(u32));
+		if (count > 0 && count <= ARRAY_SIZE(combined)) {
+			ret = of_property_read_u32_array(np, "semtech,combined-sensors",
+							 combined, count);
+			if (ret)
+				break;
+		} else {
+			/*
+			 * Either the property does not exist in the DT or the
+			 * number of entries is incorrect.
+			 */
+			break;
+		}
+		for (i = 0; i < count; i++) {
+			if (combined[i] >= SX9310_NUM_CHANNELS) {
+				/* Invalid sensor (invalid DT). */
+				break;
+			}
+			comb_mask |= BIT(combined[i]);
 		}
+		if (i < count)
+			break;
 
-		comb_mask &= 0xf;
+		reg_def->def &= ~SX9310_REG_PROX_CTRL2_COMBMODE_MASK;
 		if (comb_mask == (BIT(3) | BIT(2) | BIT(1) | BIT(0)))
 			reg_def->def |= SX9310_REG_PROX_CTRL2_COMBMODE_CS0_CS1_CS2_CS3;
 		else if (comb_mask == (BIT(1) | BIT(2)))
-- 
2.31.0.291.g576ba9dcdaf-goog