[PATCH 0/4] Add QST QMC5883P magnetometer driver

[PATCH 0/4] Add QST QMC5883P magnetometer driver

[Hardik Phalet]

This series adds initial Linux support for the QST QMC5883P, a 3-axis
anisotropic magneto-resistive (AMR) magnetometer with a 16-bit ADC that
communicates over I2C. To my knowledge there is no existing upstream
driver for this device.

The driver supports:
  - Raw magnetic field readings on X, Y, and Z axes
  - Four selectable full-scale ranges (±2 G, ±8 G, ±12 G, ±30 G)
  - Configurable output data rate (10, 50, 100, 200 Hz)
  - Configurable oversampling ratio (1, 2, 4, 8)
  - Configurable downsampling ratio (1, 2, 4, 8) via a custom sysfs
    attribute
  - Runtime PM with a 2 s autosuspend delay
  - System suspend/resume via pm_runtime_force_suspend/resume

Regmap with an rbtree cache is used throughout. CTRL_1 and CTRL_2
bit fields are accessed via regmap_field to avoid read-modify-write
races. The STATUS register is marked precious so regmap never reads
it speculatively and clears the DRDY/OVFL bits unexpectedly.

The init sequence on probe is: soft reset → wait 1 ms → deassert
reset → configure SET/RESET control → apply default ODR/OSR/DSR/RNG
→ enter normal mode. This ordering was determined empirically on
hardware to produce reliable, non-zero axis readings.

The driver is placed under drivers/staging/iio/magnetometer/ with a
TODO file tracking the remaining work before it can graduate:
  - Triggered buffer support (iio_triggered_buffer_setup)
  - DRDY interrupt support
  - Self-test implementation

Patches:
  1/4 - dt-bindings: vendor-prefixes: Add 'qst' for QST Corporation
  2/4 - dt-bindings: iio: magnetometer: Add binding for QST QMC5883P
  3/4 - staging: iio: magnetometer: Add QST QMC5883P driver
  4/4 - MAINTAINERS: Add entry for QST QMC5883P magnetometer driver

Testing
-------
Tested on a Raspberry Pi 4B running a mainline kernel (aarch64) with a
GY-271 HM-246 board connected via I2C bus 1. The chip was confirmed to
enumerate at address 0x2C via i2cdetect.

The driver was cross-compiled from Fedora (x86_64) targeting aarch64
and loaded as a module (qmc5883p.ko) with the Device Tree overlay
pointing at i2c1:0x2c.

Verification steps performed:
  - Chip ID register (0x00) reads back 0x80 on probe, confirming the
    correct device is present
  - All three axes (in_magn_x_raw, in_magn_y_raw, in_magn_z_raw) return
    non-zero, stable values when the board is held still and change
    appropriately when the board is rotated
  - in_magn_x_scale (and Y, Z) returns the expected fractional value for
    the default ±8 G range (1/37500000)
  - in_magn_sampling_frequency / _available, in_magn_oversampling_ratio /
    _available, and downsampling_ratio / downsampling_ratio_available all
    read and write correctly; the chip responds without error to each
    valid setting
  - Runtime PM: after 2 s of inactivity the device enters suspend mode
    (MODE = 0x00 confirmed via i2cdump); the next sysfs read correctly
    resumes the device and returns valid data
  - System suspend/resume (echo mem > /sys/power/state) leaves the
    driver in a consistent state; readings remain valid after resume
  - dt_binding_check passes for patch 2/4
  - Kernel builds cleanly with W=1 and no new warnings

Hardik Phalet (4):
  dt-bindings: vendor-prefixes: Add QST Corporation
  dt-bindings: iio: magnetometer: Add binding for QST QMC5883P
  Subject: [PATCH 3/4] staging: iio: magnetometer: Add QST QMC5883P
    driver
  MAINTAINERS: Add entry for QST QMC5883P magnetometer driver

 .../iio/magnetometer/qst,qmc5883p.yaml        |  48 +
 .../devicetree/bindings/vendor-prefixes.yaml  |   2 +
 MAINTAINERS                                   |   7 +
 drivers/staging/iio/Kconfig                   |   1 +
 drivers/staging/iio/Makefile                  |   1 +
 drivers/staging/iio/magnetometer/Kconfig      |  20 +
 drivers/staging/iio/magnetometer/Makefile     |   7 +
 drivers/staging/iio/magnetometer/TODO         |   5 +
 drivers/staging/iio/magnetometer/qmc5883p.c   | 819 ++++++++++++++++++
 9 files changed, 910 insertions(+)
 create mode 100644 Documentation/devicetree/bindings/iio/magnetometer/qst,qmc5883p.yaml
 create mode 100644 drivers/staging/iio/magnetometer/Kconfig
 create mode 100644 drivers/staging/iio/magnetometer/Makefile
 create mode 100644 drivers/staging/iio/magnetometer/TODO
 create mode 100644 drivers/staging/iio/magnetometer/qmc5883p.c

-- 
2.53.0

[PATCH 1/4] dt-bindings: vendor-prefixes: Add QST Corporation

[Hardik Phalet]

Add the vendor prefix 'qst' for QST Corporation, a manufacturer of
MEMS sensors.

Signed-off-by: Hardik Phalet <hardik.phalet@pm.me>
---
 Documentation/devicetree/bindings/vendor-prefixes.yaml | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/Documentation/devicetree/bindings/vendor-prefixes.yaml b/Documentation/devicetree/bindings/vendor-prefixes.yaml
index 5d2a7a8d3ac6..71a1b9087c5e 100644
--- a/Documentation/devicetree/bindings/vendor-prefixes.yaml
+++ b/Documentation/devicetree/bindings/vendor-prefixes.yaml
@@ -1244,6 +1244,8 @@ patternProperties:
     description: Shenzhen QiShenglong Industrialist Co., Ltd.
   "^qnap,.*":
     description: QNAP Systems, Inc.
+  "^qst,.*":
+    description: QST Corporation
   "^quanta,.*":
     description: Quanta Computer Inc.
   "^radxa,.*":
-- 
2.53.0

[PATCH 2/4] dt-bindings: iio: magnetometer: Add binding for QST QMC5883P

[Hardik Phalet]

Add the device tree binding document for the QST QMC5883P, a 3-axis
anisotropic magneto-resistive (AMR) sensor with a 16-bit ADC that
communicates over I2C. The binding exposes the required 'compatible'
and 'reg' properties along with an optional 'vdd-supply' for the
2.5 V–3.6 V VDD rail.

Signed-off-by: Hardik Phalet <hardik.phalet@pm.me>
---
 .../iio/magnetometer/qst,qmc5883p.yaml        | 48 +++++++++++++++++++
 1 file changed, 48 insertions(+)
 create mode 100644 Documentation/devicetree/bindings/iio/magnetometer/qst,qmc5883p.yaml

diff --git a/Documentation/devicetree/bindings/iio/magnetometer/qst,qmc5883p.yaml b/Documentation/devicetree/bindings/iio/magnetometer/qst,qmc5883p.yaml
new file mode 100644
index 000000000000..84fec10d8b9a
--- /dev/null
+++ b/Documentation/devicetree/bindings/iio/magnetometer/qst,qmc5883p.yaml
@@ -0,0 +1,48 @@
+# SPDX-License-Identifier: (GPL-2.0 OR BSD-2-Clause)
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/iio/magnetometer/qst,qmc5883p.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: QST QMC5883P 3-axis magnetometer
+
+maintainers:
+  - Hardik Phalet <hardik.phalet@pm.me>
+
+description:
+  The QMC5883P is a 3-axis anisotropic magneto-resistive (AMR) sensor with a
+  16-bit ADC. It communicates over I2C (standard and fast modes) and is
+  targeted at compass, navigation, and industrial applications.
+
+properties:
+  compatible:
+    const: qst,qmc5883p
+
+  reg:
+    maxItems: 1
+    description: I2C address of the device; the default address is 0x2c.
+
+  vdd-supply:
+    description:
+      VDD power supply (2.5 V to 3.6 V). Powers all internal analog and
+      digital functional blocks.
+
+required:
+  - compatible
+  - reg
+
+additionalProperties: false
+
+examples:
+  - |
+    i2c {
+        #address-cells = <1>;
+        #size-cells = <0>;
+
+        magnetometer@2c {
+            compatible = "qst,qmc5883p";
+            reg = <0x2c>;
+            vdd-supply = <&vdd_3v3>;
+        };
+    };
+...
-- 
2.53.0

[PATCH 3/4] staging: iio: magnetometer: Add QST QMC5883P driver

[Hardik Phalet]

Add an IIO driver for the QST QMC5883P 3-axis magnetometer. The device
communicates over I2C and is managed via regmap with an rbtree cache.
Regmap fields are used to access the individual bit fields in CTRL_1 and
CTRL_2 registers.

The driver supports:
 - Raw magnetic field readings on X, Y and Z axes
 - Four full-scale ranges (±2 G, ±8 G, ±12 G, ±30 G)
 - Configurable output data rate (10, 50, 100, 200 Hz)
 - Configurable oversampling ratio (1, 2, 4, 8)
 - Configurable downsampling ratio (1, 2, 4, 8) via a custom sysfs attr
 - Runtime PM with a 2 s autosuspend delay

Known limitations tracked in TODO:
 - No triggered buffer support
 - No DRDY interrupt support
 - Self-test register field is unused

Signed-off-by: Hardik Phalet <hardik.phalet@pm.me>
---
 drivers/staging/iio/Kconfig                 |   1 +
 drivers/staging/iio/Makefile                |   1 +
 drivers/staging/iio/magnetometer/Kconfig    |  20 +
 drivers/staging/iio/magnetometer/Makefile   |   7 +
 drivers/staging/iio/magnetometer/TODO       |   5 +
 drivers/staging/iio/magnetometer/qmc5883p.c | 819 ++++++++++++++++++++
 6 files changed, 853 insertions(+)
 create mode 100644 drivers/staging/iio/magnetometer/Kconfig
 create mode 100644 drivers/staging/iio/magnetometer/Makefile
 create mode 100644 drivers/staging/iio/magnetometer/TODO
 create mode 100644 drivers/staging/iio/magnetometer/qmc5883p.c

diff --git a/drivers/staging/iio/Kconfig b/drivers/staging/iio/Kconfig
index a60631c1f449..d363e163d248 100644
--- a/drivers/staging/iio/Kconfig
+++ b/drivers/staging/iio/Kconfig
@@ -10,5 +10,6 @@ source "drivers/staging/iio/adc/Kconfig"
 source "drivers/staging/iio/addac/Kconfig"
 source "drivers/staging/iio/frequency/Kconfig"
 source "drivers/staging/iio/impedance-analyzer/Kconfig"
+source "drivers/staging/iio/magnetometer/Kconfig"
 
 endmenu
diff --git a/drivers/staging/iio/Makefile b/drivers/staging/iio/Makefile
index 628583535393..7dcbb75d43f0 100644
--- a/drivers/staging/iio/Makefile
+++ b/drivers/staging/iio/Makefile
@@ -8,3 +8,4 @@ obj-y += adc/
 obj-y += addac/
 obj-y += frequency/
 obj-y += impedance-analyzer/
+obj-y += magnetometer/
diff --git a/drivers/staging/iio/magnetometer/Kconfig b/drivers/staging/iio/magnetometer/Kconfig
new file mode 100644
index 000000000000..d631da9578a1
--- /dev/null
+++ b/drivers/staging/iio/magnetometer/Kconfig
@@ -0,0 +1,20 @@
+# SPDX-License-Identifier: GPL-2.0-only
+#
+# Magnetometer sensors
+#
+# When adding new entries keep the list in alphabetical order
+
+menu "Magnetometer sensors"
+
+config QMC5883P
+	tristate "QMC5883P 3-Axis Magnetometer"
+	depends on I2C
+	select REGMAP_I2C
+	help
+	  Say yes here to build support for QMC5883P I2C-based
+	  3-axis magnetometer chip.
+
+	  To compile this driver as a module, choose M here: the
+	  module will be called qmc5883p.
+
+endmenu
diff --git a/drivers/staging/iio/magnetometer/Makefile b/drivers/staging/iio/magnetometer/Makefile
new file mode 100644
index 000000000000..8e650f2e3b02
--- /dev/null
+++ b/drivers/staging/iio/magnetometer/Makefile
@@ -0,0 +1,7 @@
+# SPDX-License-Identifier: GPL-2.0-only
+#
+# Makefile for staging industrial I/O Magnetometer sensor devices
+#
+# When adding new entries keep the list in alphabetical order
+
+obj-$(CONFIG_QMC5883P)	+= qmc5883p.o
diff --git a/drivers/staging/iio/magnetometer/TODO b/drivers/staging/iio/magnetometer/TODO
new file mode 100644
index 000000000000..6a8084c0dded
--- /dev/null
+++ b/drivers/staging/iio/magnetometer/TODO
@@ -0,0 +1,5 @@
+TODO
+====
+- Implement triggered buffer support (iio_triggered_buffer_setup)
+- Add interrupt (DRDY) support
+- Implement self-test (selftest regmap field is unused)
diff --git a/drivers/staging/iio/magnetometer/qmc5883p.c b/drivers/staging/iio/magnetometer/qmc5883p.c
new file mode 100644
index 000000000000..6a71dc47efb9
--- /dev/null
+++ b/drivers/staging/iio/magnetometer/qmc5883p.c
@@ -0,0 +1,819 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * qmc5883p.c - QMC5883P magnetometer driver
+ *
+ * Copyright 2026 Hardik Phalet <hardik.phalet@pm.me>
+ */
+
+#include <linux/array_size.h>
+#include <linux/bits.h>
+#include <linux/cleanup.h>
+#include <linux/delay.h>
+#include <linux/dev_printk.h>
+#include <linux/device.h>
+#include <linux/err.h>
+#include <linux/i2c.h>
+#include <linux/iio/iio.h>
+#include <linux/iio/sysfs.h>
+#include <linux/iio/types.h>
+#include <linux/mod_devicetable.h>
+#include <linux/module.h>
+#include <linux/mutex.h>
+#include <linux/pm.h>
+#include <linux/pm_runtime.h>
+#include <linux/regmap.h>
+
+/* Register definition */
+#define QMC5883P_REG_CHIP_ID 0x00
+#define QMC5883P_REG_X_LSB 0x01
+#define QMC5883P_REG_X_MSB 0x02
+#define QMC5883P_REG_Y_LSB 0x03
+#define QMC5883P_REG_Y_MSB 0x04
+#define QMC5883P_REG_Z_LSB 0x05
+#define QMC5883P_REG_Z_MSB 0x06
+#define QMC5883P_REG_STATUS 0x09
+#define QMC5883P_REG_CTRL_1 0x0A
+#define QMC5883P_REG_CTRL_2 0x0B
+
+/* Value definition */
+#define QMC5883P_MODE_SUSPEND 0x00
+#define QMC5883P_MODE_NORMAL 0x01
+#define QMC5883P_MODE_SINGLE 0x02
+#define QMC5883P_MODE_CONTINUOUS 0x03
+
+/* Output data rate */
+#define QMC5883P_ODR_10 0x00
+#define QMC5883P_ODR_50 0x01
+#define QMC5883P_ODR_100 0x02
+#define QMC5883P_ODR_200 0x03
+
+/* Oversampling rate */
+#define QMC5883P_OSR_8 0x00
+#define QMC5883P_OSR_4 0x01
+#define QMC5883P_OSR_2 0x02
+#define QMC5883P_OSR_1 0x03
+
+/* Downsampling rate */
+#define QMC5883P_DSR_1 0x00
+#define QMC5883P_DSR_2 0x01
+#define QMC5883P_DSR_4 0x02
+#define QMC5883P_DSR_8 0x03
+
+#define QMC5883P_RSTCTRL_SET_RESET \
+	0x00 /* Set and reset on, i.e. the offset of device is renewed */
+#define QMC5883P_RSTCTRL_SET_ONLY 0x01 /* Set only on */
+#define QMC5883P_RSTCTRL_OFF 0x02 /* Set and reset off */
+
+#define QMC5883P_RNG_30G 0x00
+#define QMC5883P_RNG_12G 0x01
+#define QMC5883P_RNG_08G 0x02
+#define QMC5883P_RNG_02G 0x03
+
+#define QMC5883P_DEFAULT_ODR QMC5883P_ODR_100
+#define QMC5883P_DEFAULT_OSR QMC5883P_OSR_4
+#define QMC5883P_DEFAULT_DSR QMC5883P_DSR_4
+#define QMC5883P_DEFAULT_RNG QMC5883P_RNG_08G
+
+#define QMC5883P_DRDY_POLL_US 1000
+
+#define QMC5883P_CHIP_ID 0x80
+
+#define QMC5883P_STATUS_DRDY BIT(0)
+#define QMC5883P_STATUS_OVFL BIT(1)
+
+/*
+ * Scale factors in T/LSB for IIO_VAL_FRACTIONAL (val/val2), derived from
+ * datasheet Table 2 sensitivities (LSB/G) converted to LSB/T (1 G = 1e-4 T):
+ *   sensitivity_T = sensitivity_G * 10000
+ *   scale = 1 / sensitivity_T
+ *
+ * Index matches register value: RNG<1:0> = 0b00..0b11
+ */
+static const int qmc5883p_scale[][2] = {
+	[QMC5883P_RNG_30G] = { 1, 10000000 },
+	[QMC5883P_RNG_12G] = { 1, 25000000 },
+	[QMC5883P_RNG_08G] = { 1, 37500000 },
+	[QMC5883P_RNG_02G] = { 1, 150000000 },
+};
+
+static const int qmc5883p_odr[] = {
+	[QMC5883P_ODR_10] = 10,
+	[QMC5883P_ODR_50] = 50,
+	[QMC5883P_ODR_100] = 100,
+	[QMC5883P_ODR_200] = 200,
+};
+
+static const int qmc5883p_osr[] = {
+	[QMC5883P_OSR_1] = 1,
+	[QMC5883P_OSR_2] = 2,
+	[QMC5883P_OSR_4] = 4,
+	[QMC5883P_OSR_8] = 8,
+};
+
+static const unsigned int qmc5883p_dsr[] = {
+	[QMC5883P_DSR_1] = 1,
+	[QMC5883P_DSR_2] = 2,
+	[QMC5883P_DSR_4] = 4,
+	[QMC5883P_DSR_8] = 8,
+};
+
+struct qmc5883p_rf {
+	struct regmap_field *osr;
+	struct regmap_field *dsr;
+	struct regmap_field *odr;
+	struct regmap_field *mode;
+	struct regmap_field *rng;
+	struct regmap_field *rstctrl;
+	struct regmap_field *sftrst;
+	struct regmap_field *selftest;
+	struct regmap_field *chip_id;
+};
+
+static const struct regmap_range qmc5883p_readable_ranges[] = {
+	regmap_reg_range(QMC5883P_REG_CHIP_ID, QMC5883P_REG_STATUS),
+	regmap_reg_range(QMC5883P_REG_CTRL_1, QMC5883P_REG_CTRL_2),
+};
+
+static const struct regmap_range qmc5883p_writable_ranges[] = {
+	regmap_reg_range(QMC5883P_REG_CTRL_1, QMC5883P_REG_CTRL_2),
+};
+
+/*
+ * Volatile registers: hardware updates these independently of the driver.
+ * regmap will never serve these from cache.
+ */
+static const struct regmap_range qmc5883p_volatile_ranges[] = {
+	regmap_reg_range(QMC5883P_REG_X_LSB, QMC5883P_REG_Z_MSB),
+	regmap_reg_range(QMC5883P_REG_STATUS, QMC5883P_REG_STATUS),
+};
+
+/*
+ * Precious registers: reading has a side effect (clears DRDY/OVFL bits).
+ * regmap will never read these speculatively.
+ */
+static const struct regmap_range qmc5883p_precious_ranges[] = {
+	regmap_reg_range(QMC5883P_REG_STATUS, QMC5883P_REG_STATUS),
+};
+
+static const struct regmap_access_table qmc5883p_readable_table = {
+	.yes_ranges = qmc5883p_readable_ranges,
+	.n_yes_ranges = ARRAY_SIZE(qmc5883p_readable_ranges),
+};
+
+static const struct regmap_access_table qmc5883p_writable_table = {
+	.yes_ranges = qmc5883p_writable_ranges,
+	.n_yes_ranges = ARRAY_SIZE(qmc5883p_writable_ranges),
+};
+
+static const struct regmap_access_table qmc5883p_volatile_table = {
+	.yes_ranges = qmc5883p_volatile_ranges,
+	.n_yes_ranges = ARRAY_SIZE(qmc5883p_volatile_ranges),
+};
+
+static const struct regmap_access_table qmc5883p_precious_table = {
+	.yes_ranges = qmc5883p_precious_ranges,
+	.n_yes_ranges = ARRAY_SIZE(qmc5883p_precious_ranges),
+};
+
+static const struct regmap_config qmc5883p_regmap_config = {
+	.reg_bits = 8,
+	.val_bits = 8,
+	.max_register = 0x0B,
+	.cache_type = REGCACHE_RBTREE,
+	.rd_table = &qmc5883p_readable_table,
+	.wr_table = &qmc5883p_writable_table,
+	.volatile_table = &qmc5883p_volatile_table,
+	.precious_table = &qmc5883p_precious_table,
+};
+
+struct qmc5883p_data {
+	struct device *dev;
+	struct regmap *regmap;
+	struct mutex mutex; /* protects regmap and rf field accesses */
+	struct qmc5883p_rf rf;
+};
+
+enum qmc5883p_channels {
+	AXIS_X = 0,
+	AXIS_Y,
+	AXIS_Z,
+};
+
+static const struct reg_field qmc5883p_rf_osr =
+	REG_FIELD(QMC5883P_REG_CTRL_1, 4, 5);
+static const struct reg_field qmc5883p_rf_dsr =
+	REG_FIELD(QMC5883P_REG_CTRL_1, 6, 7);
+static const struct reg_field qmc5883p_rf_odr =
+	REG_FIELD(QMC5883P_REG_CTRL_1, 2, 3);
+static const struct reg_field qmc5883p_rf_mode =
+	REG_FIELD(QMC5883P_REG_CTRL_1, 0, 1);
+static const struct reg_field qmc5883p_rf_rng =
+	REG_FIELD(QMC5883P_REG_CTRL_2, 2, 3);
+static const struct reg_field qmc5883p_rf_rstctrl =
+	REG_FIELD(QMC5883P_REG_CTRL_2, 0, 1);
+static const struct reg_field qmc5883p_rf_sftrst =
+	REG_FIELD(QMC5883P_REG_CTRL_2, 7, 7);
+static const struct reg_field qmc5883p_rf_selftest =
+	REG_FIELD(QMC5883P_REG_CTRL_2, 6, 6);
+static const struct reg_field qmc5883p_rf_chip_id =
+	REG_FIELD(QMC5883P_REG_CHIP_ID, 0, 7);
+
+static int qmc5883p_rf_init(struct qmc5883p_data *data)
+{
+	struct regmap *regmap = data->regmap;
+	struct device *dev = data->dev;
+	struct qmc5883p_rf *rf = &data->rf;
+
+	rf->osr = devm_regmap_field_alloc(dev, regmap, qmc5883p_rf_osr);
+	if (IS_ERR(rf->osr))
+		return PTR_ERR(rf->osr);
+
+	rf->dsr = devm_regmap_field_alloc(dev, regmap, qmc5883p_rf_dsr);
+	if (IS_ERR(rf->dsr))
+		return PTR_ERR(rf->dsr);
+
+	rf->odr = devm_regmap_field_alloc(dev, regmap, qmc5883p_rf_odr);
+	if (IS_ERR(rf->odr))
+		return PTR_ERR(rf->odr);
+
+	rf->mode = devm_regmap_field_alloc(dev, regmap, qmc5883p_rf_mode);
+	if (IS_ERR(rf->mode))
+		return PTR_ERR(rf->mode);
+
+	rf->rng = devm_regmap_field_alloc(dev, regmap, qmc5883p_rf_rng);
+	if (IS_ERR(rf->rng))
+		return PTR_ERR(rf->rng);
+
+	rf->rstctrl = devm_regmap_field_alloc(dev, regmap, qmc5883p_rf_rstctrl);
+	if (IS_ERR(rf->rstctrl))
+		return PTR_ERR(rf->rstctrl);
+
+	rf->sftrst = devm_regmap_field_alloc(dev, regmap, qmc5883p_rf_sftrst);
+	if (IS_ERR(rf->sftrst))
+		return PTR_ERR(rf->sftrst);
+
+	rf->selftest =
+		devm_regmap_field_alloc(dev, regmap, qmc5883p_rf_selftest);
+	if (IS_ERR(rf->selftest))
+		return PTR_ERR(rf->selftest);
+
+	rf->chip_id = devm_regmap_field_alloc(dev, regmap, qmc5883p_rf_chip_id);
+	if (IS_ERR(rf->chip_id))
+		return PTR_ERR(rf->chip_id);
+
+	return 0;
+}
+
+static int qmc5883p_verify_chip_id(struct qmc5883p_data *data)
+{
+	int ret, regval;
+
+	ret = regmap_field_read(data->rf.chip_id, &regval);
+	if (ret)
+		return dev_err_probe(data->dev, ret,
+				     "failed to read chip ID\n");
+
+	if (regval != QMC5883P_CHIP_ID)
+		return dev_err_probe(data->dev, -ENODEV,
+				     "unexpected chip ID 0x%02x, expected 0x%02x\n",
+				     regval, QMC5883P_CHIP_ID);
+	return ret;
+}
+
+static int qmc5883p_chip_init(struct qmc5883p_data *data)
+{
+	int ret;
+
+	ret = regmap_field_write(data->rf.sftrst, 1);
+	if (ret)
+		return ret;
+
+	usleep_range(1000, 2000);
+
+	ret = regmap_field_write(data->rf.sftrst, 0);
+	if (ret)
+		return ret;
+
+	ret = regmap_field_write(data->rf.rstctrl, QMC5883P_RSTCTRL_SET_RESET);
+	if (ret)
+		return ret;
+
+	ret = regmap_field_write(data->rf.rng, QMC5883P_DEFAULT_RNG);
+	if (ret)
+		return ret;
+
+	ret = regmap_field_write(data->rf.osr, QMC5883P_DEFAULT_OSR);
+	if (ret)
+		return ret;
+
+	ret = regmap_field_write(data->rf.dsr, QMC5883P_DEFAULT_DSR);
+	if (ret)
+		return ret;
+
+	ret = regmap_field_write(data->rf.odr, QMC5883P_DEFAULT_ODR);
+	if (ret)
+		return ret;
+
+	return regmap_field_write(data->rf.mode, QMC5883P_MODE_NORMAL);
+}
+
+/*
+ * qmc5883p_get_measure - read all three axes.
+ * Must be called with data->mutex held.
+ * Handles PM internally: resumes device, reads data, schedules autosuspend.
+ */
+static int qmc5883p_get_measure(struct qmc5883p_data *data, s16 *x, s16 *y,
+				s16 *z)
+{
+	int ret;
+	u8 reg_data[6];
+	unsigned int status;
+
+	ret = pm_runtime_resume_and_get(data->dev);
+	if (ret < 0)
+		return ret;
+
+	/*
+	 * Poll the status register until DRDY is set or timeout.
+	 * Read the whole register in one shot so that OVFL is captured from
+	 * the same read: reading 0x09 clears both DRDY and OVFL, so a second
+	 * read would always see OVFL=0.
+	 * At ODR=10Hz one period is 100ms; use 150ms as a safe upper bound.
+	 */
+	ret = regmap_read_poll_timeout(data->regmap, QMC5883P_REG_STATUS,
+				       status, status & QMC5883P_STATUS_DRDY,
+				       QMC5883P_DRDY_POLL_US, 150000);
+	if (ret)
+		goto out;
+
+	if (status & QMC5883P_STATUS_OVFL) {
+		dev_warn_ratelimited(data->dev,
+				     "data overflow, consider reducing field range\n");
+		ret = -ERANGE;
+		goto out;
+	}
+
+	ret = regmap_bulk_read(data->regmap, QMC5883P_REG_X_LSB, reg_data,
+			       ARRAY_SIZE(reg_data));
+	if (ret)
+		goto out;
+
+	*x = (s16)((reg_data[1] << 8) | reg_data[0]);
+	*y = (s16)((reg_data[3] << 8) | reg_data[2]);
+	*z = (s16)((reg_data[5] << 8) | reg_data[4]);
+
+out:
+	pm_runtime_mark_last_busy(data->dev);
+	pm_runtime_put_autosuspend(data->dev);
+	return ret;
+}
+
+static int qmc5883p_write_scale(struct qmc5883p_data *data, int val, int val2)
+{
+	int i;
+
+	for (i = 0; i < ARRAY_SIZE(qmc5883p_scale); i++) {
+		if (qmc5883p_scale[i][0] == val && qmc5883p_scale[i][1] == val2)
+			return regmap_field_write(data->rf.rng, i);
+	}
+
+	return -EINVAL;
+}
+
+static int qmc5883p_write_odr(struct qmc5883p_data *data, int val)
+{
+	int i;
+
+	for (i = 0; i < ARRAY_SIZE(qmc5883p_odr); i++) {
+		if (qmc5883p_odr[i] == val)
+			return regmap_field_write(data->rf.odr, i);
+	}
+
+	return -EINVAL;
+}
+
+static int qmc5883p_write_osr(struct qmc5883p_data *data, int val)
+{
+	int i;
+
+	for (i = 0; i < ARRAY_SIZE(qmc5883p_osr); i++) {
+		if (qmc5883p_osr[i] == val)
+			return regmap_field_write(data->rf.osr, i);
+	}
+
+	return -EINVAL;
+}
+
+static ssize_t downsampling_ratio_show(struct device *dev,
+				       struct device_attribute *attr, char *buf)
+{
+	struct iio_dev *indio_dev = dev_get_drvdata(dev);
+	struct qmc5883p_data *data = iio_priv(indio_dev);
+	unsigned int regval;
+	int ret;
+
+	guard(mutex)(&data->mutex);
+
+	ret = regmap_field_read(data->rf.dsr, &regval);
+	if (ret)
+		return ret;
+
+	return sysfs_emit(buf, "%u\n", qmc5883p_dsr[regval]);
+}
+
+static ssize_t downsampling_ratio_store(struct device *dev,
+					struct device_attribute *attr,
+					const char *buf, size_t len)
+{
+	struct iio_dev *indio_dev = dev_get_drvdata(dev);
+	struct qmc5883p_data *data = iio_priv(indio_dev);
+	unsigned int val;
+	int i, ret, restore;
+
+	ret = kstrtouint(buf, 10, &val);
+	if (ret)
+		return ret;
+
+	guard(mutex)(&data->mutex);
+
+	ret = pm_runtime_resume_and_get(dev);
+	if (ret)
+		return ret;
+
+	ret = regmap_field_write(data->rf.mode, QMC5883P_MODE_SUSPEND);
+	if (ret)
+		goto out;
+
+	ret = -EINVAL;
+	for (i = 0; i < ARRAY_SIZE(qmc5883p_dsr); i++) {
+		if (qmc5883p_dsr[i] == val) {
+			ret = regmap_field_write(data->rf.dsr, i);
+			break;
+		}
+	}
+
+	restore = regmap_field_write(data->rf.mode, QMC5883P_MODE_NORMAL);
+	if (restore && !ret)
+		ret = restore;
+
+out:
+	pm_runtime_mark_last_busy(dev);
+	pm_runtime_put_autosuspend(dev);
+	return ret ? ret : (ssize_t)len;
+}
+
+static int qmc5883p_read_raw(struct iio_dev *indio_dev,
+			     const struct iio_chan_spec *chan, int *val,
+			     int *val2, long mask)
+{
+	s16 x, y, z;
+	struct qmc5883p_data *data = iio_priv(indio_dev);
+	int ret;
+	unsigned int regval;
+
+	guard(mutex)(&data->mutex);
+
+	switch (mask) {
+	case IIO_CHAN_INFO_RAW:
+		ret = qmc5883p_get_measure(data, &x, &y, &z);
+		if (ret < 0)
+			return ret;
+		switch (chan->address) {
+		case AXIS_X:
+			*val = x;
+			break;
+		case AXIS_Y:
+			*val = y;
+			break;
+		case AXIS_Z:
+			*val = z;
+			break;
+		}
+		return IIO_VAL_INT;
+
+	case IIO_CHAN_INFO_SCALE:
+		ret = regmap_field_read(data->rf.rng, &regval);
+		if (ret < 0)
+			return ret;
+		*val = qmc5883p_scale[regval][0];
+		*val2 = qmc5883p_scale[regval][1];
+		return IIO_VAL_FRACTIONAL;
+
+	case IIO_CHAN_INFO_SAMP_FREQ:
+		ret = regmap_field_read(data->rf.odr, &regval);
+		if (ret < 0)
+			return ret;
+		*val = qmc5883p_odr[regval];
+		return IIO_VAL_INT;
+
+	case IIO_CHAN_INFO_OVERSAMPLING_RATIO:
+		ret = regmap_field_read(data->rf.osr, &regval);
+		if (ret < 0)
+			return ret;
+		*val = qmc5883p_osr[regval];
+		return IIO_VAL_INT;
+	}
+
+	return -EINVAL;
+}
+
+static int qmc5883p_write_raw(struct iio_dev *indio_dev,
+			      struct iio_chan_spec const *chan, int val,
+			      int val2, long mask)
+{
+	struct qmc5883p_data *data = iio_priv(indio_dev);
+	int ret, restore;
+
+	guard(mutex)(&data->mutex);
+
+	ret = pm_runtime_resume_and_get(data->dev);
+	if (ret)
+		return ret;
+
+	ret = regmap_field_write(data->rf.mode, QMC5883P_MODE_SUSPEND);
+	if (ret)
+		goto out;
+
+	switch (mask) {
+	case IIO_CHAN_INFO_SAMP_FREQ:
+		ret = qmc5883p_write_odr(data, val);
+		break;
+	case IIO_CHAN_INFO_OVERSAMPLING_RATIO:
+		ret = qmc5883p_write_osr(data, val);
+		break;
+	case IIO_CHAN_INFO_SCALE:
+		ret = qmc5883p_write_scale(data, val, val2);
+		break;
+	default:
+		ret = -EINVAL;
+		break;
+	}
+
+	restore = regmap_field_write(data->rf.mode, QMC5883P_MODE_NORMAL);
+	if (restore && !ret)
+		ret = restore;
+
+out:
+	pm_runtime_mark_last_busy(data->dev);
+	pm_runtime_put_autosuspend(data->dev);
+	return ret;
+}
+
+/*
+ * qmc5883p_read_avail - expose available values to userspace.
+ *
+ * Creates the _available sysfs attributes automatically:
+ *   in_magn_sampling_frequency_available
+ *   in_magn_oversampling_ratio_available
+ *   in_magn_scale_available
+ */
+static int qmc5883p_read_avail(struct iio_dev *indio_dev,
+			       struct iio_chan_spec const *chan,
+			       const int **vals, int *type, int *length,
+			       long mask)
+{
+	switch (mask) {
+	case IIO_CHAN_INFO_SAMP_FREQ:
+		*vals = qmc5883p_odr;
+		*type = IIO_VAL_INT;
+		*length = ARRAY_SIZE(qmc5883p_odr);
+		return IIO_AVAIL_LIST;
+
+	case IIO_CHAN_INFO_OVERSAMPLING_RATIO:
+		*vals = qmc5883p_osr;
+		*type = IIO_VAL_INT;
+		*length = ARRAY_SIZE(qmc5883p_osr);
+		return IIO_AVAIL_LIST;
+
+	case IIO_CHAN_INFO_SCALE:
+		*vals = (const int *)qmc5883p_scale;
+		*type = IIO_VAL_FRACTIONAL;
+		*length = ARRAY_SIZE(qmc5883p_scale) * 2;
+		return IIO_AVAIL_LIST;
+
+	default:
+		return -EINVAL;
+	}
+}
+
+static IIO_DEVICE_ATTR(downsampling_ratio, 0644, downsampling_ratio_show,
+		       downsampling_ratio_store, 0);
+static IIO_CONST_ATTR(downsampling_ratio_available, "1 2 4 8");
+
+static struct attribute *qmc5883p_attributes[] = {
+	&iio_dev_attr_downsampling_ratio.dev_attr.attr,
+	&iio_const_attr_downsampling_ratio_available.dev_attr.attr, NULL
+};
+
+static const struct attribute_group qmc5883p_attribute_group = {
+	.attrs = qmc5883p_attributes,
+};
+
+static const struct iio_info qmc5883p_info = {
+	.attrs = &qmc5883p_attribute_group,
+	.read_raw = qmc5883p_read_raw,
+	.write_raw = qmc5883p_write_raw,
+	.read_avail = qmc5883p_read_avail,
+};
+
+static const struct iio_chan_spec qmc5883p_channels[] = {
+	{
+		.type = IIO_MAGN,
+		.channel2 = IIO_MOD_X,
+		.modified = 1,
+		.address = AXIS_X,
+		.info_mask_separate = BIT(IIO_CHAN_INFO_RAW) |
+				      BIT(IIO_CHAN_INFO_SCALE),
+		.info_mask_separate_available = BIT(IIO_CHAN_INFO_SCALE),
+		.info_mask_shared_by_type =
+			BIT(IIO_CHAN_INFO_SAMP_FREQ) |
+			BIT(IIO_CHAN_INFO_OVERSAMPLING_RATIO),
+		.info_mask_shared_by_type_available =
+			BIT(IIO_CHAN_INFO_SAMP_FREQ) |
+			BIT(IIO_CHAN_INFO_OVERSAMPLING_RATIO),
+	},
+	{
+		.type = IIO_MAGN,
+		.channel2 = IIO_MOD_Y,
+		.modified = 1,
+		.address = AXIS_Y,
+		.info_mask_separate = BIT(IIO_CHAN_INFO_RAW) |
+				      BIT(IIO_CHAN_INFO_SCALE),
+		.info_mask_separate_available = BIT(IIO_CHAN_INFO_SCALE),
+		.info_mask_shared_by_type =
+			BIT(IIO_CHAN_INFO_SAMP_FREQ) |
+			BIT(IIO_CHAN_INFO_OVERSAMPLING_RATIO),
+		.info_mask_shared_by_type_available =
+			BIT(IIO_CHAN_INFO_SAMP_FREQ) |
+			BIT(IIO_CHAN_INFO_OVERSAMPLING_RATIO),
+	},
+	{
+		.type = IIO_MAGN,
+		.channel2 = IIO_MOD_Z,
+		.modified = 1,
+		.address = AXIS_Z,
+		.info_mask_separate = BIT(IIO_CHAN_INFO_RAW) |
+				      BIT(IIO_CHAN_INFO_SCALE),
+		.info_mask_separate_available = BIT(IIO_CHAN_INFO_SCALE),
+		.info_mask_shared_by_type =
+			BIT(IIO_CHAN_INFO_SAMP_FREQ) |
+			BIT(IIO_CHAN_INFO_OVERSAMPLING_RATIO),
+		.info_mask_shared_by_type_available =
+			BIT(IIO_CHAN_INFO_SAMP_FREQ) |
+			BIT(IIO_CHAN_INFO_OVERSAMPLING_RATIO),
+	},
+};
+
+static void qmc5883p_runtime_pm_disable(void *dev)
+{
+	pm_runtime_disable(dev);
+	pm_runtime_set_suspended(dev);
+}
+
+static int qmc5883p_probe(struct i2c_client *client)
+{
+	struct device *dev = &client->dev;
+	struct qmc5883p_data *data;
+	struct iio_dev *indio_dev;
+	struct regmap *regmap;
+	int ret;
+
+	indio_dev = devm_iio_device_alloc(dev, sizeof(*data));
+	if (!indio_dev)
+		return -ENOMEM;
+
+	regmap = devm_regmap_init_i2c(client, &qmc5883p_regmap_config);
+	if (IS_ERR(regmap))
+		return dev_err_probe(dev, PTR_ERR(regmap),
+				     "regmap initialization failed\n");
+
+	data = iio_priv(indio_dev);
+	data->dev = dev;
+	data->regmap = regmap;
+	mutex_init(&data->mutex);
+
+	i2c_set_clientdata(client, indio_dev);
+
+	ret = qmc5883p_rf_init(data);
+	if (ret)
+		return dev_err_probe(dev, ret,
+				     "failed to initialize regmap fields\n");
+
+	ret = qmc5883p_verify_chip_id(data);
+	if (ret)
+		return ret;
+
+	ret = qmc5883p_chip_init(data);
+	if (ret)
+		return dev_err_probe(dev, ret, "failed to initialize chip\n");
+
+	indio_dev->name = "qmc5883p";
+	indio_dev->info = &qmc5883p_info;
+	indio_dev->modes = INDIO_DIRECT_MODE;
+	indio_dev->channels = qmc5883p_channels;
+	indio_dev->num_channels = ARRAY_SIZE(qmc5883p_channels);
+
+	pm_runtime_set_autosuspend_delay(dev, 2000);
+	pm_runtime_use_autosuspend(dev);
+
+	pm_runtime_set_active(dev);
+	pm_runtime_enable(dev);
+
+	ret = devm_add_action_or_reset(dev,
+				       (void (*)(void *))qmc5883p_runtime_pm_disable,
+				       dev);
+	if (ret)
+		return ret;
+
+	pm_runtime_mark_last_busy(dev);
+
+	ret = devm_iio_device_register(dev, indio_dev);
+	if (ret)
+		return dev_err_probe(dev, ret,
+				     "failed to register IIO device\n");
+	return 0;
+}
+
+static int qmc5883p_runtime_suspend(struct device *dev)
+{
+	struct iio_dev *indio_dev = dev_get_drvdata(dev);
+	struct qmc5883p_data *data = iio_priv(indio_dev);
+
+	return regmap_field_write(data->rf.mode, QMC5883P_MODE_SUSPEND);
+}
+
+static int qmc5883p_runtime_resume(struct device *dev)
+{
+	struct iio_dev *indio_dev = dev_get_drvdata(dev);
+	struct qmc5883p_data *data = iio_priv(indio_dev);
+	int ret;
+
+	ret = regmap_field_write(data->rf.mode, QMC5883P_MODE_NORMAL);
+	if (ret)
+		return ret;
+
+	usleep_range(10000, 11000);
+	return 0;
+}
+
+static int qmc5883p_runtime_idle(struct device *dev)
+{
+	return 0;
+}
+
+static int qmc5883p_system_suspend(struct device *dev)
+{
+	return pm_runtime_force_suspend(dev);
+}
+
+static int qmc5883p_system_resume(struct device *dev)
+{
+	return pm_runtime_force_resume(dev);
+}
+
+static void qmc5883p_remove(struct i2c_client *client)
+{
+	struct iio_dev *indio_dev = i2c_get_clientdata(client);
+	struct qmc5883p_data *data = iio_priv(indio_dev);
+
+	/*
+	 * Best effort: put device to sleep on removal.
+	 * Ignore error since we cannot do anything useful with it here.
+	 * Runtime PM disable is handled by the devm cleanup action registered
+	 * in probe.
+	 */
+	regmap_field_write(data->rf.mode, QMC5883P_MODE_SUSPEND);
+}
+
+static const struct dev_pm_ops qmc5883p_dev_pm_ops = {
+	SYSTEM_SLEEP_PM_OPS(qmc5883p_system_suspend, qmc5883p_system_resume)
+	RUNTIME_PM_OPS(qmc5883p_runtime_suspend, qmc5883p_runtime_resume, NULL)
+};
+
+static const struct of_device_id qmc5883p_of_match[] = {
+	{ .compatible = "qst,qmc5883p" },
+	{}
+};
+MODULE_DEVICE_TABLE(of, qmc5883p_of_match);
+
+static const struct i2c_device_id qmc5883p_id[] = {
+	{ "qmc5883p", 0 },
+	{},
+};
+MODULE_DEVICE_TABLE(i2c, qmc5883p_id);
+
+static struct i2c_driver qmc5883p_driver = {
+	.driver = {
+		.name = "qmc5883p",
+		.of_match_table = qmc5883p_of_match,
+		.pm = pm_ptr(&qmc5883p_dev_pm_ops),
+	},
+	.probe = qmc5883p_probe,
+	.remove = qmc5883p_remove,
+	.id_table = qmc5883p_id,
+};
+module_i2c_driver(qmc5883p_driver);
+
+MODULE_AUTHOR("Hardik Phalet <hardik.phalet@pm.me>");
+MODULE_DESCRIPTION("QMC5883P magnetic sensor driver");
+MODULE_LICENSE("GPL");
-- 
2.53.0

Re: [PATCH 3/4] staging: iio: magnetometer: Add QST QMC5883P driver

[Luka Gejak]

On Thu Apr 9, 2026 at 6:24 PM CEST, Hardik Phalet wrote:
> Add an IIO driver for the QST QMC5883P 3-axis magnetometer. The device
> communicates over I2C and is managed via regmap with an rbtree cache.
> Regmap fields are used to access the individual bit fields in CTRL_1 and
> CTRL_2 registers.
>
> The driver supports:
>  - Raw magnetic field readings on X, Y and Z axes
>  - Four full-scale ranges (±2 G, ±8 G, ±12 G, ±30 G)
>  - Configurable output data rate (10, 50, 100, 200 Hz)
>  - Configurable oversampling ratio (1, 2, 4, 8)
>  - Configurable downsampling ratio (1, 2, 4, 8) via a custom sysfs attr
>  - Runtime PM with a 2 s autosuspend delay
>
> Known limitations tracked in TODO:
>  - No triggered buffer support
>  - No DRDY interrupt support
>  - Self-test register field is unused
>
> Signed-off-by: Hardik Phalet <hardik.phalet@pm.me>
> ---
>  drivers/staging/iio/Kconfig                 |   1 +
>  drivers/staging/iio/Makefile                |   1 +
>  drivers/staging/iio/magnetometer/Kconfig    |  20 +
>  drivers/staging/iio/magnetometer/Makefile   |   7 +
>  drivers/staging/iio/magnetometer/TODO       |   5 +
>  drivers/staging/iio/magnetometer/qmc5883p.c | 819 ++++++++++++++++++++
>  6 files changed, 853 insertions(+)
>  create mode 100644 drivers/staging/iio/magnetometer/Kconfig
>  create mode 100644 drivers/staging/iio/magnetometer/Makefile
>  create mode 100644 drivers/staging/iio/magnetometer/TODO
>  create mode 100644 drivers/staging/iio/magnetometer/qmc5883p.c
>
> diff --git a/drivers/staging/iio/Kconfig b/drivers/staging/iio/Kconfig
> index a60631c1f449..d363e163d248 100644
> --- a/drivers/staging/iio/Kconfig
> +++ b/drivers/staging/iio/Kconfig
> @@ -10,5 +10,6 @@ source "drivers/staging/iio/adc/Kconfig"
>  source "drivers/staging/iio/addac/Kconfig"
>  source "drivers/staging/iio/frequency/Kconfig"
>  source "drivers/staging/iio/impedance-analyzer/Kconfig"
> +source "drivers/staging/iio/magnetometer/Kconfig"
>  
>  endmenu
> diff --git a/drivers/staging/iio/Makefile b/drivers/staging/iio/Makefile
> index 628583535393..7dcbb75d43f0 100644
> --- a/drivers/staging/iio/Makefile
> +++ b/drivers/staging/iio/Makefile
> @@ -8,3 +8,4 @@ obj-y += adc/
>  obj-y += addac/
>  obj-y += frequency/
>  obj-y += impedance-analyzer/
> +obj-y += magnetometer/
> diff --git a/drivers/staging/iio/magnetometer/Kconfig b/drivers/staging/iio/magnetometer/Kconfig
> new file mode 100644
> index 000000000000..d631da9578a1
> --- /dev/null
> +++ b/drivers/staging/iio/magnetometer/Kconfig
> @@ -0,0 +1,20 @@
> +# SPDX-License-Identifier: GPL-2.0-only
> +#
> +# Magnetometer sensors
> +#
> +# When adding new entries keep the list in alphabetical order
> +
> +menu "Magnetometer sensors"
> +
> +config QMC5883P
> +	tristate "QMC5883P 3-Axis Magnetometer"
> +	depends on I2C
> +	select REGMAP_I2C
> +	help
> +	  Say yes here to build support for QMC5883P I2C-based
> +	  3-axis magnetometer chip.
> +
> +	  To compile this driver as a module, choose M here: the
> +	  module will be called qmc5883p.
> +
> +endmenu
> diff --git a/drivers/staging/iio/magnetometer/Makefile b/drivers/staging/iio/magnetometer/Makefile
> new file mode 100644
> index 000000000000..8e650f2e3b02
> --- /dev/null
> +++ b/drivers/staging/iio/magnetometer/Makefile
> @@ -0,0 +1,7 @@
> +# SPDX-License-Identifier: GPL-2.0-only
> +#
> +# Makefile for staging industrial I/O Magnetometer sensor devices
> +#
> +# When adding new entries keep the list in alphabetical order
> +
> +obj-$(CONFIG_QMC5883P)	+= qmc5883p.o
> diff --git a/drivers/staging/iio/magnetometer/TODO b/drivers/staging/iio/magnetometer/TODO
> new file mode 100644
> index 000000000000..6a8084c0dded
> --- /dev/null
> +++ b/drivers/staging/iio/magnetometer/TODO
> @@ -0,0 +1,5 @@
> +TODO
> +====
> +- Implement triggered buffer support (iio_triggered_buffer_setup)
> +- Add interrupt (DRDY) support
> +- Implement self-test (selftest regmap field is unused)
> diff --git a/drivers/staging/iio/magnetometer/qmc5883p.c b/drivers/staging/iio/magnetometer/qmc5883p.c
> new file mode 100644
> index 000000000000..6a71dc47efb9
> --- /dev/null
> +++ b/drivers/staging/iio/magnetometer/qmc5883p.c
> @@ -0,0 +1,819 @@
> +// SPDX-License-Identifier: GPL-2.0-only
> +/*
> + * qmc5883p.c - QMC5883P magnetometer driver
> + *
> + * Copyright 2026 Hardik Phalet <hardik.phalet@pm.me>
> + */
> +
> +#include <linux/array_size.h>
> +#include <linux/bits.h>
> +#include <linux/cleanup.h>
> +#include <linux/delay.h>
> +#include <linux/dev_printk.h>
> +#include <linux/device.h>
> +#include <linux/err.h>
> +#include <linux/i2c.h>
> +#include <linux/iio/iio.h>
> +#include <linux/iio/sysfs.h>
> +#include <linux/iio/types.h>
> +#include <linux/mod_devicetable.h>
> +#include <linux/module.h>
> +#include <linux/mutex.h>
> +#include <linux/pm.h>
> +#include <linux/pm_runtime.h>
> +#include <linux/regmap.h>
> +
> +/* Register definition */
> +#define QMC5883P_REG_CHIP_ID 0x00
> +#define QMC5883P_REG_X_LSB 0x01
> +#define QMC5883P_REG_X_MSB 0x02
> +#define QMC5883P_REG_Y_LSB 0x03
> +#define QMC5883P_REG_Y_MSB 0x04
> +#define QMC5883P_REG_Z_LSB 0x05
> +#define QMC5883P_REG_Z_MSB 0x06
> +#define QMC5883P_REG_STATUS 0x09
> +#define QMC5883P_REG_CTRL_1 0x0A
> +#define QMC5883P_REG_CTRL_2 0x0B
> +
> +/* Value definition */
> +#define QMC5883P_MODE_SUSPEND 0x00
> +#define QMC5883P_MODE_NORMAL 0x01
> +#define QMC5883P_MODE_SINGLE 0x02
> +#define QMC5883P_MODE_CONTINUOUS 0x03
> +
> +/* Output data rate */
> +#define QMC5883P_ODR_10 0x00
> +#define QMC5883P_ODR_50 0x01
> +#define QMC5883P_ODR_100 0x02
> +#define QMC5883P_ODR_200 0x03
> +
> +/* Oversampling rate */
> +#define QMC5883P_OSR_8 0x00
> +#define QMC5883P_OSR_4 0x01
> +#define QMC5883P_OSR_2 0x02
> +#define QMC5883P_OSR_1 0x03
> +
> +/* Downsampling rate */
> +#define QMC5883P_DSR_1 0x00
> +#define QMC5883P_DSR_2 0x01
> +#define QMC5883P_DSR_4 0x02
> +#define QMC5883P_DSR_8 0x03
> +
> +#define QMC5883P_RSTCTRL_SET_RESET \
> +	0x00 /* Set and reset on, i.e. the offset of device is renewed */
> +#define QMC5883P_RSTCTRL_SET_ONLY 0x01 /* Set only on */
> +#define QMC5883P_RSTCTRL_OFF 0x02 /* Set and reset off */
> +
> +#define QMC5883P_RNG_30G 0x00
> +#define QMC5883P_RNG_12G 0x01
> +#define QMC5883P_RNG_08G 0x02
> +#define QMC5883P_RNG_02G 0x03
> +
> +#define QMC5883P_DEFAULT_ODR QMC5883P_ODR_100
> +#define QMC5883P_DEFAULT_OSR QMC5883P_OSR_4
> +#define QMC5883P_DEFAULT_DSR QMC5883P_DSR_4
> +#define QMC5883P_DEFAULT_RNG QMC5883P_RNG_08G
> +
> +#define QMC5883P_DRDY_POLL_US 1000
> +
> +#define QMC5883P_CHIP_ID 0x80
> +
> +#define QMC5883P_STATUS_DRDY BIT(0)
> +#define QMC5883P_STATUS_OVFL BIT(1)
> +
> +/*
> + * Scale factors in T/LSB for IIO_VAL_FRACTIONAL (val/val2), derived from
> + * datasheet Table 2 sensitivities (LSB/G) converted to LSB/T (1 G = 1e-4 T):
> + *   sensitivity_T = sensitivity_G * 10000
> + *   scale = 1 / sensitivity_T
> + *
> + * Index matches register value: RNG<1:0> = 0b00..0b11
> + */
> +static const int qmc5883p_scale[][2] = {
> +	[QMC5883P_RNG_30G] = { 1, 10000000 },
> +	[QMC5883P_RNG_12G] = { 1, 25000000 },
> +	[QMC5883P_RNG_08G] = { 1, 37500000 },
> +	[QMC5883P_RNG_02G] = { 1, 150000000 },
> +};
> +
> +static const int qmc5883p_odr[] = {
> +	[QMC5883P_ODR_10] = 10,
> +	[QMC5883P_ODR_50] = 50,
> +	[QMC5883P_ODR_100] = 100,
> +	[QMC5883P_ODR_200] = 200,
> +};
> +
> +static const int qmc5883p_osr[] = {
> +	[QMC5883P_OSR_1] = 1,
> +	[QMC5883P_OSR_2] = 2,
> +	[QMC5883P_OSR_4] = 4,
> +	[QMC5883P_OSR_8] = 8,
> +};
> +
> +static const unsigned int qmc5883p_dsr[] = {
> +	[QMC5883P_DSR_1] = 1,
> +	[QMC5883P_DSR_2] = 2,
> +	[QMC5883P_DSR_4] = 4,
> +	[QMC5883P_DSR_8] = 8,
> +};
> +
> +struct qmc5883p_rf {
> +	struct regmap_field *osr;
> +	struct regmap_field *dsr;
> +	struct regmap_field *odr;
> +	struct regmap_field *mode;
> +	struct regmap_field *rng;
> +	struct regmap_field *rstctrl;
> +	struct regmap_field *sftrst;
> +	struct regmap_field *selftest;
> +	struct regmap_field *chip_id;
> +};
> +
> +static const struct regmap_range qmc5883p_readable_ranges[] = {
> +	regmap_reg_range(QMC5883P_REG_CHIP_ID, QMC5883P_REG_STATUS),
> +	regmap_reg_range(QMC5883P_REG_CTRL_1, QMC5883P_REG_CTRL_2),
> +};
> +
> +static const struct regmap_range qmc5883p_writable_ranges[] = {
> +	regmap_reg_range(QMC5883P_REG_CTRL_1, QMC5883P_REG_CTRL_2),
> +};
> +
> +/*
> + * Volatile registers: hardware updates these independently of the driver.
> + * regmap will never serve these from cache.
> + */
> +static const struct regmap_range qmc5883p_volatile_ranges[] = {
> +	regmap_reg_range(QMC5883P_REG_X_LSB, QMC5883P_REG_Z_MSB),
> +	regmap_reg_range(QMC5883P_REG_STATUS, QMC5883P_REG_STATUS),
> +};
> +
> +/*
> + * Precious registers: reading has a side effect (clears DRDY/OVFL bits).
> + * regmap will never read these speculatively.
> + */
> +static const struct regmap_range qmc5883p_precious_ranges[] = {
> +	regmap_reg_range(QMC5883P_REG_STATUS, QMC5883P_REG_STATUS),
> +};
> +
> +static const struct regmap_access_table qmc5883p_readable_table = {
> +	.yes_ranges = qmc5883p_readable_ranges,
> +	.n_yes_ranges = ARRAY_SIZE(qmc5883p_readable_ranges),
> +};
> +
> +static const struct regmap_access_table qmc5883p_writable_table = {
> +	.yes_ranges = qmc5883p_writable_ranges,
> +	.n_yes_ranges = ARRAY_SIZE(qmc5883p_writable_ranges),
> +};
> +
> +static const struct regmap_access_table qmc5883p_volatile_table = {
> +	.yes_ranges = qmc5883p_volatile_ranges,
> +	.n_yes_ranges = ARRAY_SIZE(qmc5883p_volatile_ranges),
> +};
> +
> +static const struct regmap_access_table qmc5883p_precious_table = {
> +	.yes_ranges = qmc5883p_precious_ranges,
> +	.n_yes_ranges = ARRAY_SIZE(qmc5883p_precious_ranges),
> +};
> +
> +static const struct regmap_config qmc5883p_regmap_config = {
> +	.reg_bits = 8,
> +	.val_bits = 8,
> +	.max_register = 0x0B,
> +	.cache_type = REGCACHE_RBTREE,
> +	.rd_table = &qmc5883p_readable_table,
> +	.wr_table = &qmc5883p_writable_table,
> +	.volatile_table = &qmc5883p_volatile_table,
> +	.precious_table = &qmc5883p_precious_table,
> +};
> +
> +struct qmc5883p_data {
> +	struct device *dev;
> +	struct regmap *regmap;
> +	struct mutex mutex; /* protects regmap and rf field accesses */
> +	struct qmc5883p_rf rf;
> +};
> +
> +enum qmc5883p_channels {
> +	AXIS_X = 0,
> +	AXIS_Y,
> +	AXIS_Z,
> +};
> +
> +static const struct reg_field qmc5883p_rf_osr =
> +	REG_FIELD(QMC5883P_REG_CTRL_1, 4, 5);
> +static const struct reg_field qmc5883p_rf_dsr =
> +	REG_FIELD(QMC5883P_REG_CTRL_1, 6, 7);
> +static const struct reg_field qmc5883p_rf_odr =
> +	REG_FIELD(QMC5883P_REG_CTRL_1, 2, 3);
> +static const struct reg_field qmc5883p_rf_mode =
> +	REG_FIELD(QMC5883P_REG_CTRL_1, 0, 1);
> +static const struct reg_field qmc5883p_rf_rng =
> +	REG_FIELD(QMC5883P_REG_CTRL_2, 2, 3);
> +static const struct reg_field qmc5883p_rf_rstctrl =
> +	REG_FIELD(QMC5883P_REG_CTRL_2, 0, 1);
> +static const struct reg_field qmc5883p_rf_sftrst =
> +	REG_FIELD(QMC5883P_REG_CTRL_2, 7, 7);
> +static const struct reg_field qmc5883p_rf_selftest =
> +	REG_FIELD(QMC5883P_REG_CTRL_2, 6, 6);
> +static const struct reg_field qmc5883p_rf_chip_id =
> +	REG_FIELD(QMC5883P_REG_CHIP_ID, 0, 7);
> +
> +static int qmc5883p_rf_init(struct qmc5883p_data *data)
> +{
> +	struct regmap *regmap = data->regmap;
> +	struct device *dev = data->dev;
> +	struct qmc5883p_rf *rf = &data->rf;
> +
> +	rf->osr = devm_regmap_field_alloc(dev, regmap, qmc5883p_rf_osr);
> +	if (IS_ERR(rf->osr))
> +		return PTR_ERR(rf->osr);
> +
> +	rf->dsr = devm_regmap_field_alloc(dev, regmap, qmc5883p_rf_dsr);
> +	if (IS_ERR(rf->dsr))
> +		return PTR_ERR(rf->dsr);
> +
> +	rf->odr = devm_regmap_field_alloc(dev, regmap, qmc5883p_rf_odr);
> +	if (IS_ERR(rf->odr))
> +		return PTR_ERR(rf->odr);
> +
> +	rf->mode = devm_regmap_field_alloc(dev, regmap, qmc5883p_rf_mode);
> +	if (IS_ERR(rf->mode))
> +		return PTR_ERR(rf->mode);
> +
> +	rf->rng = devm_regmap_field_alloc(dev, regmap, qmc5883p_rf_rng);
> +	if (IS_ERR(rf->rng))
> +		return PTR_ERR(rf->rng);
> +
> +	rf->rstctrl = devm_regmap_field_alloc(dev, regmap, qmc5883p_rf_rstctrl);
> +	if (IS_ERR(rf->rstctrl))
> +		return PTR_ERR(rf->rstctrl);
> +
> +	rf->sftrst = devm_regmap_field_alloc(dev, regmap, qmc5883p_rf_sftrst);
> +	if (IS_ERR(rf->sftrst))
> +		return PTR_ERR(rf->sftrst);
> +
> +	rf->selftest =
> +		devm_regmap_field_alloc(dev, regmap, qmc5883p_rf_selftest);
> +	if (IS_ERR(rf->selftest))
> +		return PTR_ERR(rf->selftest);
> +
> +	rf->chip_id = devm_regmap_field_alloc(dev, regmap, qmc5883p_rf_chip_id);
> +	if (IS_ERR(rf->chip_id))
> +		return PTR_ERR(rf->chip_id);
> +
> +	return 0;
> +}
> +
> +static int qmc5883p_verify_chip_id(struct qmc5883p_data *data)
> +{
> +	int ret, regval;
> +
> +	ret = regmap_field_read(data->rf.chip_id, &regval);
> +	if (ret)
> +		return dev_err_probe(data->dev, ret,
> +				     "failed to read chip ID\n");
> +
> +	if (regval != QMC5883P_CHIP_ID)
> +		return dev_err_probe(data->dev, -ENODEV,
> +				     "unexpected chip ID 0x%02x, expected 0x%02x\n",
> +				     regval, QMC5883P_CHIP_ID);
> +	return ret;
> +}
> +
> +static int qmc5883p_chip_init(struct qmc5883p_data *data)
> +{
> +	int ret;
> +
> +	ret = regmap_field_write(data->rf.sftrst, 1);
> +	if (ret)
> +		return ret;
> +
> +	usleep_range(1000, 2000);
> +
> +	ret = regmap_field_write(data->rf.sftrst, 0);
> +	if (ret)
> +		return ret;
> +
> +	ret = regmap_field_write(data->rf.rstctrl, QMC5883P_RSTCTRL_SET_RESET);
> +	if (ret)
> +		return ret;
> +
> +	ret = regmap_field_write(data->rf.rng, QMC5883P_DEFAULT_RNG);
> +	if (ret)
> +		return ret;
> +
> +	ret = regmap_field_write(data->rf.osr, QMC5883P_DEFAULT_OSR);
> +	if (ret)
> +		return ret;
> +
> +	ret = regmap_field_write(data->rf.dsr, QMC5883P_DEFAULT_DSR);
> +	if (ret)
> +		return ret;
> +
> +	ret = regmap_field_write(data->rf.odr, QMC5883P_DEFAULT_ODR);
> +	if (ret)
> +		return ret;
> +
> +	return regmap_field_write(data->rf.mode, QMC5883P_MODE_NORMAL);
> +}
> +
> +/*
> + * qmc5883p_get_measure - read all three axes.
> + * Must be called with data->mutex held.
> + * Handles PM internally: resumes device, reads data, schedules autosuspend.
> + */
> +static int qmc5883p_get_measure(struct qmc5883p_data *data, s16 *x, s16 *y,
> +				s16 *z)
> +{

...

> +
> +	*x = (s16)((reg_data[1] << 8) | reg_data[0]);
> +	*y = (s16)((reg_data[3] << 8) | reg_data[2]);
> +	*z = (s16)((reg_data[5] << 8) | reg_data[4]);
> +

While functionally correct, the standard kernel idiom for deserializing 
contiguous byte arrays is to use the unaligned access helpers. Consider 
including <linux/unaligned.h> at the top of the file and using 
get_unaligned_le16(). Also since it returns a u16, you must keep the 
(s16) cast. Something like:
*x = (s16)get_unaligned_le16(&reg_data[0]);
*y = (s16)get_unaligned_le16(&reg_data[2]);
*z = (s16)get_unaligned_le16(&reg_data[4]);

> +out:
> +	pm_runtime_mark_last_busy(data->dev);
> +	pm_runtime_put_autosuspend(data->dev);
> +	return ret;
> +}
> +
> +static int qmc5883p_write_scale(struct qmc5883p_data *data, int val, int val2)
> +{
> +	int i;
> +
> +	for (i = 0; i < ARRAY_SIZE(qmc5883p_scale); i++) {
> +		if (qmc5883p_scale[i][0] == val && qmc5883p_scale[i][1] == val2)
> +			return regmap_field_write(data->rf.rng, i);
> +	}
> +
> +	return -EINVAL;
> +}
> +
> +static int qmc5883p_write_odr(struct qmc5883p_data *data, int val)
> +{
> +	int i;
> +
> +	for (i = 0; i < ARRAY_SIZE(qmc5883p_odr); i++) {
> +		if (qmc5883p_odr[i] == val)
> +			return regmap_field_write(data->rf.odr, i);
> +	}
> +
> +	return -EINVAL;
> +}
> +
> +static int qmc5883p_write_osr(struct qmc5883p_data *data, int val)
> +{
> +	int i;
> +
> +	for (i = 0; i < ARRAY_SIZE(qmc5883p_osr); i++) {
> +		if (qmc5883p_osr[i] == val)
> +			return regmap_field_write(data->rf.osr, i);
> +	}
> +
> +	return -EINVAL;
> +}
> +
> +static ssize_t downsampling_ratio_show(struct device *dev,
> +				       struct device_attribute *attr, char *buf)
> +{
> +	struct iio_dev *indio_dev = dev_get_drvdata(dev);
> +	struct qmc5883p_data *data = iio_priv(indio_dev);
> +	unsigned int regval;
> +	int ret;
> +
> +	guard(mutex)(&data->mutex);
> +
> +	ret = regmap_field_read(data->rf.dsr, &regval);
> +	if (ret)
> +		return ret;
> +
> +	return sysfs_emit(buf, "%u\n", qmc5883p_dsr[regval]);
> +}
> +
> +static ssize_t downsampling_ratio_store(struct device *dev,
> +					struct device_attribute *attr,
> +					const char *buf, size_t len)
> +{

...

> +	guard(mutex)(&data->mutex);
> +
> +	ret = pm_runtime_resume_and_get(dev);

For iio sysfs attributes, the dev pointer belongs to the iio device 
(&indio_dev->dev), not the i2c parent device where runtime pm was 
initialized. Calling pm operations on the iio device will lead to pm 
refcount imbalances and potential kernel warnings. You should use 
data->dev for all pm_runtime_* calls inside custom sysfs callbacks. 
Something like ret = pm_runtime_resume_and_get(data->dev);

> +	if (ret)
> +		return ret;
> +
> +	ret = regmap_field_write(data->rf.mode, QMC5883P_MODE_SUSPEND);
> +	if (ret)
> +		goto out;
> +
> +	ret = -EINVAL;
> +	for (i = 0; i < ARRAY_SIZE(qmc5883p_dsr); i++) {
> +		if (qmc5883p_dsr[i] == val) {
> +			ret = regmap_field_write(data->rf.dsr, i);
> +			break;
> +		}
> +	}
> +
> +	restore = regmap_field_write(data->rf.mode, QMC5883P_MODE_NORMAL);
> +	if (restore && !ret)
> +		ret = restore;
> +
> +out:
> +	pm_runtime_mark_last_busy(dev);
> +	pm_runtime_put_autosuspend(dev);

You should change these to use data->dev as well.

> +	return ret ? ret : (ssize_t)len;
> +}
> +
> +static int qmc5883p_read_raw(struct iio_dev *indio_dev,
> +			     const struct iio_chan_spec *chan, int *val,
> +			     int *val2, long mask)
> +{
> +	s16 x, y, z;
> +	struct qmc5883p_data *data = iio_priv(indio_dev);
> +	int ret;
> +	unsigned int regval;
> +
> +	guard(mutex)(&data->mutex);
> +
> +	switch (mask) {
> +	case IIO_CHAN_INFO_RAW:
> +		ret = qmc5883p_get_measure(data, &x, &y, &z);
> +		if (ret < 0)
> +			return ret;
> +		switch (chan->address) {
> +		case AXIS_X:
> +			*val = x;
> +			break;
> +		case AXIS_Y:
> +			*val = y;
> +			break;
> +		case AXIS_Z:
> +			*val = z;
> +			break;
> +		}
> +		return IIO_VAL_INT;
> +
> +	case IIO_CHAN_INFO_SCALE:
> +		ret = regmap_field_read(data->rf.rng, &regval);
> +		if (ret < 0)
> +			return ret;
> +		*val = qmc5883p_scale[regval][0];
> +		*val2 = qmc5883p_scale[regval][1];
> +		return IIO_VAL_FRACTIONAL;
> +
> +	case IIO_CHAN_INFO_SAMP_FREQ:
> +		ret = regmap_field_read(data->rf.odr, &regval);
> +		if (ret < 0)
> +			return ret;
> +		*val = qmc5883p_odr[regval];
> +		return IIO_VAL_INT;
> +
> +	case IIO_CHAN_INFO_OVERSAMPLING_RATIO:
> +		ret = regmap_field_read(data->rf.osr, &regval);
> +		if (ret < 0)
> +			return ret;
> +		*val = qmc5883p_osr[regval];
> +		return IIO_VAL_INT;
> +	}
> +
> +	return -EINVAL;
> +}
> +
> +static int qmc5883p_write_raw(struct iio_dev *indio_dev,
> +			      struct iio_chan_spec const *chan, int val,
> +			      int val2, long mask)
> +{
> +	struct qmc5883p_data *data = iio_priv(indio_dev);
> +	int ret, restore;
> +
> +	guard(mutex)(&data->mutex);
> +
> +	ret = pm_runtime_resume_and_get(data->dev);
> +	if (ret)
> +		return ret;
> +
> +	ret = regmap_field_write(data->rf.mode, QMC5883P_MODE_SUSPEND);
> +	if (ret)
> +		goto out;
> +
> +	switch (mask) {
> +	case IIO_CHAN_INFO_SAMP_FREQ:
> +		ret = qmc5883p_write_odr(data, val);
> +		break;
> +	case IIO_CHAN_INFO_OVERSAMPLING_RATIO:
> +		ret = qmc5883p_write_osr(data, val);
> +		break;
> +	case IIO_CHAN_INFO_SCALE:
> +		ret = qmc5883p_write_scale(data, val, val2);
> +		break;
> +	default:
> +		ret = -EINVAL;
> +		break;
> +	}
> +
> +	restore = regmap_field_write(data->rf.mode, QMC5883P_MODE_NORMAL);
> +	if (restore && !ret)
> +		ret = restore;
> +
> +out:
> +	pm_runtime_mark_last_busy(data->dev);
> +	pm_runtime_put_autosuspend(data->dev);
> +	return ret;
> +}
> +
> +/*
> + * qmc5883p_read_avail - expose available values to userspace.
> + *
> + * Creates the _available sysfs attributes automatically:
> + *   in_magn_sampling_frequency_available
> + *   in_magn_oversampling_ratio_available
> + *   in_magn_scale_available
> + */
> +static int qmc5883p_read_avail(struct iio_dev *indio_dev,
> +			       struct iio_chan_spec const *chan,
> +			       const int **vals, int *type, int *length,
> +			       long mask)
> +{
> +	switch (mask) {
> +	case IIO_CHAN_INFO_SAMP_FREQ:
> +		*vals = qmc5883p_odr;
> +		*type = IIO_VAL_INT;
> +		*length = ARRAY_SIZE(qmc5883p_odr);
> +		return IIO_AVAIL_LIST;
> +
> +	case IIO_CHAN_INFO_OVERSAMPLING_RATIO:
> +		*vals = qmc5883p_osr;
> +		*type = IIO_VAL_INT;
> +		*length = ARRAY_SIZE(qmc5883p_osr);
> +		return IIO_AVAIL_LIST;
> +
> +	case IIO_CHAN_INFO_SCALE:
> +		*vals = (const int *)qmc5883p_scale;
> +		*type = IIO_VAL_FRACTIONAL;
> +		*length = ARRAY_SIZE(qmc5883p_scale) * 2;
> +		return IIO_AVAIL_LIST;
> +
> +	default:
> +		return -EINVAL;
> +	}
> +}
> +
> +static IIO_DEVICE_ATTR(downsampling_ratio, 0644, downsampling_ratio_show,
> +		       downsampling_ratio_store, 0);
> +static IIO_CONST_ATTR(downsampling_ratio_available, "1 2 4 8");
> +
> +static struct attribute *qmc5883p_attributes[] = {
> +	&iio_dev_attr_downsampling_ratio.dev_attr.attr,
> +	&iio_const_attr_downsampling_ratio_available.dev_attr.attr, NULL
> +};
> +
> +static const struct attribute_group qmc5883p_attribute_group = {
> +	.attrs = qmc5883p_attributes,
> +};
> +
> +static const struct iio_info qmc5883p_info = {
> +	.attrs = &qmc5883p_attribute_group,
> +	.read_raw = qmc5883p_read_raw,
> +	.write_raw = qmc5883p_write_raw,
> +	.read_avail = qmc5883p_read_avail,
> +};
> +
> +static const struct iio_chan_spec qmc5883p_channels[] = {
> +	{
> +		.type = IIO_MAGN,
> +		.channel2 = IIO_MOD_X,
> +		.modified = 1,
> +		.address = AXIS_X,
> +		.info_mask_separate = BIT(IIO_CHAN_INFO_RAW) |
> +				      BIT(IIO_CHAN_INFO_SCALE),
> +		.info_mask_separate_available = BIT(IIO_CHAN_INFO_SCALE),
> +		.info_mask_shared_by_type =
> +			BIT(IIO_CHAN_INFO_SAMP_FREQ) |
> +			BIT(IIO_CHAN_INFO_OVERSAMPLING_RATIO),
> +		.info_mask_shared_by_type_available =
> +			BIT(IIO_CHAN_INFO_SAMP_FREQ) |
> +			BIT(IIO_CHAN_INFO_OVERSAMPLING_RATIO),
> +	},
> +	{
> +		.type = IIO_MAGN,
> +		.channel2 = IIO_MOD_Y,
> +		.modified = 1,
> +		.address = AXIS_Y,
> +		.info_mask_separate = BIT(IIO_CHAN_INFO_RAW) |
> +				      BIT(IIO_CHAN_INFO_SCALE),
> +		.info_mask_separate_available = BIT(IIO_CHAN_INFO_SCALE),
> +		.info_mask_shared_by_type =
> +			BIT(IIO_CHAN_INFO_SAMP_FREQ) |
> +			BIT(IIO_CHAN_INFO_OVERSAMPLING_RATIO),
> +		.info_mask_shared_by_type_available =
> +			BIT(IIO_CHAN_INFO_SAMP_FREQ) |
> +			BIT(IIO_CHAN_INFO_OVERSAMPLING_RATIO),
> +	},
> +	{
> +		.type = IIO_MAGN,
> +		.channel2 = IIO_MOD_Z,
> +		.modified = 1,
> +		.address = AXIS_Z,
> +		.info_mask_separate = BIT(IIO_CHAN_INFO_RAW) |
> +				      BIT(IIO_CHAN_INFO_SCALE),
> +		.info_mask_separate_available = BIT(IIO_CHAN_INFO_SCALE),
> +		.info_mask_shared_by_type =
> +			BIT(IIO_CHAN_INFO_SAMP_FREQ) |
> +			BIT(IIO_CHAN_INFO_OVERSAMPLING_RATIO),
> +		.info_mask_shared_by_type_available =
> +			BIT(IIO_CHAN_INFO_SAMP_FREQ) |
> +			BIT(IIO_CHAN_INFO_OVERSAMPLING_RATIO),
> +	},
> +};
> +
> +static void qmc5883p_runtime_pm_disable(void *dev)
> +{
> +	pm_runtime_disable(dev);
> +	pm_runtime_set_suspended(dev);
> +}
> +
> +static int qmc5883p_probe(struct i2c_client *client)
> +{
> +	struct device *dev = &client->dev;

Your dt-binding correctly documents an optional vdd-supply for the 
2.5V-3.6V rail, but the driver never parses or enables it. If a board 
physically powers down this regulator during system suspend or relies on
the driver to enable it at boot, the driver will fail. Please add 
devm_regulator_get_optional() and enable the regulator here. Also, you 
should ensure that your system resume callbacks correctly re-apply the 
chip's initialization sequence if power is lost during suspend.

> +	struct qmc5883p_data *data;
> +	struct iio_dev *indio_dev;
> +	struct regmap *regmap;
> +	int ret;
> +
> +	indio_dev = devm_iio_device_alloc(dev, sizeof(*data));
> +	if (!indio_dev)
> +		return -ENOMEM;
> +
> +	regmap = devm_regmap_init_i2c(client, &qmc5883p_regmap_config);
> +	if (IS_ERR(regmap))
> +		return dev_err_probe(dev, PTR_ERR(regmap),
> +				     "regmap initialization failed\n");
> +
> +	data = iio_priv(indio_dev);
> +	data->dev = dev;
> +	data->regmap = regmap;
> +	mutex_init(&data->mutex);
> +
> +	i2c_set_clientdata(client, indio_dev);
> +
> +	ret = qmc5883p_rf_init(data);
> +	if (ret)
> +		return dev_err_probe(dev, ret,
> +				     "failed to initialize regmap fields\n");
> +
> +	ret = qmc5883p_verify_chip_id(data);
> +	if (ret)
> +		return ret;
> +
> +	ret = qmc5883p_chip_init(data);
> +	if (ret)
> +		return dev_err_probe(dev, ret, "failed to initialize chip\n");
> +
> +	indio_dev->name = "qmc5883p";
> +	indio_dev->info = &qmc5883p_info;
> +	indio_dev->modes = INDIO_DIRECT_MODE;
> +	indio_dev->channels = qmc5883p_channels;
> +	indio_dev->num_channels = ARRAY_SIZE(qmc5883p_channels);
> +
> +	pm_runtime_set_autosuspend_delay(dev, 2000);
> +	pm_runtime_use_autosuspend(dev);
> +
> +	pm_runtime_set_active(dev);
> +	pm_runtime_enable(dev);
> +
> +	ret = devm_add_action_or_reset(dev,
> +				       (void (*)(void *))qmc5883p_runtime_pm_disable,
> +				       dev);

Casting function pointers like (void (*)(void *)) violates strict kcfi 
checks, which will cause a kernel panic on modern architectures 
(like arm64) compiled with cfi enabled. The pm core already provides a 
safe helper for this. Plese drop your custom qmc5883p_runtime_pm_disable
function and the devm_add_action_or_reset call, and simply use 
ret = devm_pm_runtime_enable(dev);

> +	if (ret)
> +		return ret;
> +
> +	pm_runtime_mark_last_busy(dev);
> +
> +	ret = devm_iio_device_register(dev, indio_dev);

Because you use devm_iio_device_register(), the iio interface is 
unregistered automatically during the devres unwinding phase, which 
happens after your .remove() callback completes. This creates a race 
window. A concurrent userspace sysfs read/write could trigger a pm 
resume exactly while or after remove() is putting the chip to sleep. To 
fix this, create a custom devm action (via devm_add_action_or_reset) to 
write QMC5883P_MODE_SUSPEND to the chip, and register it before this 
devm_iio_device_register() call. Because devres unwinds in lifo order, 
this guarantees the iio interface is fully unregistered before the 
hardware is suspended.

> +	if (ret)
> +		return dev_err_probe(dev, ret,
> +				     "failed to register IIO device\n");
> +	return 0;
> +}
> +
> +static int qmc5883p_runtime_suspend(struct device *dev)
> +{
> +	struct iio_dev *indio_dev = dev_get_drvdata(dev);
> +	struct qmc5883p_data *data = iio_priv(indio_dev);
> +
> +	return regmap_field_write(data->rf.mode, QMC5883P_MODE_SUSPEND);
> +}
> +
> +static int qmc5883p_runtime_resume(struct device *dev)
> +{
> +	struct iio_dev *indio_dev = dev_get_drvdata(dev);
> +	struct qmc5883p_data *data = iio_priv(indio_dev);
> +	int ret;
> +
> +	ret = regmap_field_write(data->rf.mode, QMC5883P_MODE_NORMAL);
> +	if (ret)
> +		return ret;
> +
> +	usleep_range(10000, 11000);
> +	return 0;
> +}
> +
> +static int qmc5883p_runtime_idle(struct device *dev)
> +{
> +	return 0;
> +}
> +
> +static int qmc5883p_system_suspend(struct device *dev)
> +{
> +	return pm_runtime_force_suspend(dev);
> +}
> +
> +static int qmc5883p_system_resume(struct device *dev)
> +{
> +	return pm_runtime_force_resume(dev);
> +}
> +
> +static void qmc5883p_remove(struct i2c_client *client)
> +{
> +	struct iio_dev *indio_dev = i2c_get_clientdata(client);
> +	struct qmc5883p_data *data = iio_priv(indio_dev);
> +
> +	/*
> +	 * Best effort: put device to sleep on removal.
> +	 * Ignore error since we cannot do anything useful with it here.
> +	 * Runtime PM disable is handled by the devm cleanup action registered
> +	 * in probe.
> +	 */
> +	regmap_field_write(data->rf.mode, QMC5883P_MODE_SUSPEND);
> +}

Once you move the suspend logic into a devm action in probe() (as 
mentioned above), you can delete this qmc5883p_remove() function and the
.remove hook in the i2c_driver struct entirely.

> +
> +static const struct dev_pm_ops qmc5883p_dev_pm_ops = {
> +	SYSTEM_SLEEP_PM_OPS(qmc5883p_system_suspend, qmc5883p_system_resume)
> +	RUNTIME_PM_OPS(qmc5883p_runtime_suspend, qmc5883p_runtime_resume, NULL)
> +};
> +
> +static const struct of_device_id qmc5883p_of_match[] = {
> +	{ .compatible = "qst,qmc5883p" },
> +	{}
> +};
> +MODULE_DEVICE_TABLE(of, qmc5883p_of_match);
> +
> +static const struct i2c_device_id qmc5883p_id[] = {
> +	{ "qmc5883p", 0 },
> +	{},
> +};
> +MODULE_DEVICE_TABLE(i2c, qmc5883p_id);
> +
> +static struct i2c_driver qmc5883p_driver = {
> +	.driver = {
> +		.name = "qmc5883p",
> +		.of_match_table = qmc5883p_of_match,
> +		.pm = pm_ptr(&qmc5883p_dev_pm_ops),
> +	},
> +	.probe = qmc5883p_probe,
> +	.remove = qmc5883p_remove,
> +	.id_table = qmc5883p_id,
> +};
> +module_i2c_driver(qmc5883p_driver);
> +
> +MODULE_AUTHOR("Hardik Phalet <hardik.phalet@pm.me>");
> +MODULE_DESCRIPTION("QMC5883P magnetic sensor driver");
> +MODULE_LICENSE("GPL");

Re: [PATCH 3/4] staging: iio: magnetometer: Add QST QMC5883P driver

[Hardik Phalet]

On Thu Apr 9, 2026 at 11:24 PM IST, Luka Gejak wrote:
> On Thu Apr 9, 2026 at 6:24 PM CEST, Hardik Phalet wrote:
>
> While functionally correct, the standard kernel idiom for deserializing
> contiguous byte arrays is to use the unaligned access helpers. Consider
> including <linux/unaligned.h> at the top of the file and using
> get_unaligned_le16(). Also since it returns a u16, you must keep the
> (s16) cast. Something like:
> *x = (s16)get_unaligned_le16(&reg_data[0]);
> *y = (s16)get_unaligned_le16(&reg_data[2]);
> *z = (s16)get_unaligned_le16(&reg_data[4]);
>
> For iio sysfs attributes, the dev pointer belongs to the iio device
> (&indio_dev->dev), not the i2c parent device where runtime pm was
> initialized. Calling pm operations on the iio device will lead to pm
> refcount imbalances and potential kernel warnings. You should use
> data->dev for all pm_runtime_* calls inside custom sysfs callbacks.
> Something like ret = pm_runtime_resume_and_get(data->dev);
>
>
> You should change these to use data->dev as well.
>
> Your dt-binding correctly documents an optional vdd-supply for the
> 2.5V-3.6V rail, but the driver never parses or enables it. If a board
> physically powers down this regulator during system suspend or relies on
> the driver to enable it at boot, the driver will fail. Please add
> devm_regulator_get_optional() and enable the regulator here. Also, you
> should ensure that your system resume callbacks correctly re-apply the
> chip's initialization sequence if power is lost during suspend.
>
> Casting function pointers like (void (*)(void *)) violates strict kcfi
> checks, which will cause a kernel panic on modern architectures
> (like arm64) compiled with cfi enabled. The pm core already provides a
> safe helper for this. Plese drop your custom qmc5883p_runtime_pm_disable
> function and the devm_add_action_or_reset call, and simply use
> ret = devm_pm_runtime_enable(dev);
>
> Because you use devm_iio_device_register(), the iio interface is
> unregistered automatically during the devres unwinding phase, which
> happens after your .remove() callback completes. This creates a race
> window. A concurrent userspace sysfs read/write could trigger a pm
> resume exactly while or after remove() is putting the chip to sleep. To
> fix this, create a custom devm action (via devm_add_action_or_reset) to
> write QMC5883P_MODE_SUSPEND to the chip, and register it before this
> devm_iio_device_register() call. Because devres unwinds in lifo order,
> this guarantees the iio interface is fully unregistered before the
> hardware is suspended.
>
> Once you move the suspend logic into a devm action in probe() (as
> mentioned above), you can delete this qmc5883p_remove() function and the
> .remove hook in the i2c_driver struct entirely.

Thanks for the thorough review.

All the points are clear and I'll address them in v2.

Regards,
Hardik

[PATCH 4/4] MAINTAINERS: Add entry for QST QMC5883P magnetometer driver

[Hardik Phalet]

Add a MAINTAINERS entry for the QST QMC5883P staging IIO driver,
covering the driver source and its device tree binding.

Signed-off-by: Hardik Phalet <hardik.phalet@pm.me>
---
 MAINTAINERS | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/MAINTAINERS b/MAINTAINERS
index a92290fffa16..d0b9bfceb283 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -20274,6 +20274,13 @@ F:	Documentation/networking/device_drivers/ethernet/freescale/dpaa2/overview.rst
 F:	drivers/bus/fsl-mc/
 F:	include/uapi/linux/fsl_mc.h
 
+QST QMC5883P MAGNETOMETER DRIVER
+M:	Hardik Phalet <hardik.phalet@pm.me>
+L:	linux-iio@vger.kernel.org
+S:	Maintained
+F:	Documentation/devicetree/bindings/iio/magnetometer/qst,qmc5883p.yaml
+F:	drivers/staging/iio/magnetometer/
+
 QT1010 MEDIA DRIVER
 L:	linux-media@vger.kernel.org
 S:	Orphan
-- 
2.53.0