[PATCH v3 0/2] iio: light: Add Capella CM3217 ambient light sensor

[PATCH v3 0/2] iio: light: Add Capella CM3217 ambient light sensor

[Patrick Fischer via B4 Relay]

The Capella CM3217 is a small ambient light sensor without registers.
NVIDIA used it in the Tegra Note 7 and the Shield Tablet. Mainline has
no driver for it: cm32181 and cm3232 expect registers and an ID, the
CM3217 has neither.

Patch 1 adds the binding, patch 2 the driver with raw value, scale and
integration time. The datasheet is not public, so the bit fields come
from NVIDIA's downstream drivers and the scale from Capella's published
detection range. Patch 2 explains both.

Tested on a Tegra Note 7 (P1640) with v7.3 and the driver built as a
module, the device created through new_device. In room light all 32
combinations of integration time and scale gave the same illuminance
within the count resolution (6.0 to 7.3 lux), and the first read after
each change matched the second one. The raw counts scale linearly with
both fields. Svyatoslav Ryhel also tried it on the P1988 variant of the
Tegra Note 7.

Probing through the device tree works with the real supply (vdd_dev,
Palmas LDO6), and unloading and reloading the module twice brought the
device back each time. Next to a phone light sensor the readings were
about 7 to 20 times lower. NVIDIA's Android HAL for this tablet
multiplies the count by 2.1505 at the same 2 T/100 ms setting, which is
7.2 times the scale here, so most of that is the dark cover window. With
that factor the tablet was within 15 % of the phone in bright light but
a factor of three lower in dim room light; I could not tell whether that
was my setup.

v3 was run again on the P1640, through the device tree with both
addresses in reg and through new_device without a device tree node: in
both cases the driver binds to 0x10 and claims 0x11, and all 32
settings give the same scale and integration time values as v2. With
the device tree, unloading and reloading the module twice freed and
claimed the second address again. Suspend/resume was not tested.

There is no MAINTAINERS entry: drivers/iio/light/cm* is covered by the
Capella entry and the binding by IIO. I am happy to add one if you
prefer.

The device tree node for the Tegra Note 7 will follow with Svyatoslav's
tegratab series.

Tool use (see Documentation/process/generated-content.rst): this series
was prepared with an LLM coding assistant (Claude Code). It read the
NVIDIA downstream drivers and Capella's product data, wrote the driver,
the binding and the texts from my instructions, and ran the build and
binding checks. I reviewed the code and ran the tests on the device.

---
Changes in v3:
- Binding: list both I2C addresses in reg, one description each
  (Conor).
- Driver: take the second address from the second reg entry, with 0x11
  as fallback when there is no firmware node (new_device). Svyatoslav,
  I kept your Tested-by as a device tree with only the first address
  still works through the fallback, but a quick retest would be
  welcome.
- Driver: write the resolution constant as 0.01875 lux times 800 ms in
  nanolux * ms, so that NANO is no longer part of it (Andy).
- Driver: split the scale into its integer and nano parts with a named
  helper macro (Andy).
- Driver: static_assert() on one line, the conversion margin added to
  conv_ms with a comment, FIELD_MODIFY() for IT_T, and the error return
  in probe inside scoped_guard() (Andy).
- No functional change: the scale and integration time tables in the
  object file are identical to v2. struct cm3217_data was checked with
  pahole: one 2-byte hole on 32-bit ARM, and no field order makes it
  smaller as ktime_t needs 8-byte alignment, so the order stays (Andy).
- Tested again on the device, see above.
- Link to v2: https://patch.msgid.link/20261106-upstream-iio-cm3217-v2-0-d97adde9171c@tsv-stahl-riesa.de

Changes in v2:
- Binding: describe the two I2C addresses under reg, including what each
  one is used for (Jonathan).
- Driver: replace the scale list that was recomputed on every change of
  the integration time by a const table built at compile time;
  read_avail() returns the row for the current integration time, so no
  table is rewritten while a caller may hold a pointer to it (Jonathan,
  Sashiko).
- Driver: write the resolution constant with NANO and explain its unit
  (Jonathan).
- Driver: add cm3217_power_down() for the shutdown write used in three
  places (Jonathan), and a helper for the table lookups in write_raw()
  so the loop counter can live in the for statement (Jonathan).
- Driver: take the conversion time from the integration time table and
  drop the separate table in milliseconds.
- Pick up Svyatoslav's Tested-by on patch 2 (given on v1).
- Commit messages: name the downstream trees, note that the 4 T field
  value differs from the vendor header, drop "driver" from the binding
  text.
- Rebase onto the current iio togreg branch (based on v7.4-rc1).
- No functional change intended. The 32 scale values match the v1
  computation. Run again on the Tegra Note 7 (P1640) as a module: each
  integration time lists the same scales as with v1, all 32 settings are
  accepted and read back, invalid values are rejected, and the sensor is
  shut down when the device is removed.
- Link to v1: https://patch.msgid.link/20261101-upstream-iio-cm3217-v1-0-5e1724cae7b7@tsv-stahl-riesa.de

---
Patrick Fischer (2):
      dt-bindings: iio: light: Add Capella CM3217
      iio: light: Add Capella CM3217 ambient light sensor driver

 .../bindings/iio/light/capella,cm3217.yaml         |  50 +++
 drivers/iio/light/Kconfig                          |  10 +
 drivers/iio/light/Makefile                         |   1 +
 drivers/iio/light/cm3217.c                         | 419 +++++++++++++++++++++
 4 files changed, 480 insertions(+)
---
base-commit: 1390ca4953a7400ca932cb49635f02c727f885a6
change-id: 20261101-upstream-iio-cm3217-e3f14c4760e5

Best regards,
--  
Patrick Fischer <admin@tsv-stahl-riesa.de>

[PATCH v3 1/2] dt-bindings: iio: light: Add Capella CM3217

[Patrick Fischer via B4 Relay]

From: Patrick Fischer <admin@tsv-stahl-riesa.de>

The Capella CM3217 is an ambient light sensor with an I2C interface but
without registers and without an interrupt line. It always answers on
the two fixed addresses 0x10 and 0x11, which are both listed in reg.

The sensor is used in the NVIDIA Tegra Note 7 and the NVIDIA Shield
Tablet.

Signed-off-by: Patrick Fischer <admin@tsv-stahl-riesa.de>
---
 .../bindings/iio/light/capella,cm3217.yaml         | 50 ++++++++++++++++++++++
 1 file changed, 50 insertions(+)

diff --git a/Documentation/devicetree/bindings/iio/light/capella,cm3217.yaml b/Documentation/devicetree/bindings/iio/light/capella,cm3217.yaml
new file mode 100644
index 000000000000..9aba05949a27
--- /dev/null
+++ b/Documentation/devicetree/bindings/iio/light/capella,cm3217.yaml
@@ -0,0 +1,50 @@
+# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/iio/light/capella,cm3217.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: Capella CM3217 ambient light sensor
+
+maintainers:
+  - Patrick Fischer <admin@tsv-stahl-riesa.de>
+
+description:
+  The CM3217 is an I2C ambient light sensor without registers or interrupt
+  line.
+
+properties:
+  compatible:
+    const: capella,cm3217
+
+  reg:
+    items:
+      - description:
+          Command byte 1 (shutdown and IT_T) on write, high byte of the light
+          count on read. Fixed at 0x10.
+      - description:
+          Command byte 2 (FD_IT) on write, low byte of the light count on
+          read. Fixed at 0x11.
+
+  vdd-supply: true
+
+required:
+  - compatible
+  - reg
+  - vdd-supply
+
+additionalProperties: false
+
+examples:
+  - |
+    i2c {
+        #address-cells = <1>;
+        #size-cells = <0>;
+
+        light-sensor@10 {
+            compatible = "capella,cm3217";
+            reg = <0x10>, <0x11>;
+            vdd-supply = <&vdd_2v85_sen>;
+        };
+    };
+...

-- 
2.56.0

Re: [PATCH v3 1/2] dt-bindings: iio: light: Add Capella CM3217

[Jonathan Cameron]

On Fri, 13 Nov 2026 20:58:59 +0100
Patrick Fischer via B4 Relay <devnull+admin.tsv-stahl-riesa.de@kernel.org> wrote:

> From: Patrick Fischer <admin@tsv-stahl-riesa.de>
> 
> The Capella CM3217 is an ambient light sensor with an I2C interface but
> without registers and without an interrupt line. It always answers on
> the two fixed addresses 0x10 and 0x11, which are both listed in reg.
> 
> The sensor is used in the NVIDIA Tegra Note 7 and the NVIDIA Shield
> Tablet.
> 
> Signed-off-by: Patrick Fischer <admin@tsv-stahl-riesa.de>
> ---
>  .../bindings/iio/light/capella,cm3217.yaml         | 50 ++++++++++++++++++++++
>  1 file changed, 50 insertions(+)
> 
> diff --git a/Documentation/devicetree/bindings/iio/light/capella,cm3217.yaml b/Documentation/devicetree/bindings/iio/light/capella,cm3217.yaml
> new file mode 100644
> index 000000000000..9aba05949a27
> --- /dev/null
> +++ b/Documentation/devicetree/bindings/iio/light/capella,cm3217.yaml
> @@ -0,0 +1,50 @@
> +# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
> +%YAML 1.2
> +---
> +$id: http://devicetree.org/schemas/iio/light/capella,cm3217.yaml#
> +$schema: http://devicetree.org/meta-schemas/core.yaml#
> +
> +title: Capella CM3217 ambient light sensor
> +
> +maintainers:
> +  - Patrick Fischer <admin@tsv-stahl-riesa.de>
> +
> +description:
> +  The CM3217 is an I2C ambient light sensor without registers or interrupt
> +  line.
I'd drop the 'without registers or interrupt line' as one isn't relevant to DT
and the other one is seen by there not being an interrupts entry in the properties.

Other than that, looks fine to me.

Thanks

Jonathan

> +
> +properties:
> +  compatible:
> +    const: capella,cm3217
> +
> +  reg:
> +    items:
> +      - description:
> +          Command byte 1 (shutdown and IT_T) on write, high byte of the light
> +          count on read. Fixed at 0x10.
> +      - description:
> +          Command byte 2 (FD_IT) on write, low byte of the light count on
> +          read. Fixed at 0x11.
> +
> +  vdd-supply: true
> +
> +required:
> +  - compatible
> +  - reg
> +  - vdd-supply
> +
> +additionalProperties: false
> +
> +examples:
> +  - |
> +    i2c {
> +        #address-cells = <1>;
> +        #size-cells = <0>;
> +
> +        light-sensor@10 {
> +            compatible = "capella,cm3217";
> +            reg = <0x10>, <0x11>;
> +            vdd-supply = <&vdd_2v85_sen>;
> +        };
> +    };
> +...
> 

[PATCH v3 2/2] iio: light: Add Capella CM3217 ambient light sensor driver

[Patrick Fischer via B4 Relay]

From: Patrick Fischer <admin@tsv-stahl-riesa.de>

The CM3217 has no registers and no ID. Writing a byte to address 0x10
or 0x11 sets command byte 1 or 2, reading a byte from 0x10 or 0x11
returns the high or low byte of the 16-bit light count. The driver
takes the second address from the second reg entry and falls back to
0x11 when there is no firmware node, as with new_device.

Command byte 1 holds the shutdown bit and the IT_T field (1/2 T, 1 T,
2 T or 4 T), command byte 2 the FD_IT field (800 ms down to 66 ms). The
count scales linearly with both. The driver exposes FD_IT as the
integration time and IT_T through the scale, so the scale list offers
four ranges for each integration time.

The datasheet is not public. The bit fields, the reserved bits that are
written as 1 and the startup setting of 2 T and 100 ms come from NVIDIA's
downstream drivers (drivers/staging/iio/light/cm3217.c in the 3.4 kernel
rel-tegranote-r8 and the 3.10 kernel
android-tegra-flounder-3.10-nougat-mr1.1). One value differs: the vendor
header defines 4 T as 4 << 2, which is outside the two-bit field. On a
Tegra Note 7 field value 3 gave four times the 1 T count, so the driver
uses that. For the resolution, Capella
gives a range of 0.01875 to 119156 lux. The driver takes 0.01875 lux
per count at 4 T and 800 ms. This matches both the upper end (65535
counts at 1/2 T and 66 ms) and the 0.3 lux per count that the NVIDIA
3.4 driver uses at 2 T and 100 ms.

The sensor has no data-ready flag, and a new setting only takes effect
when the conversion in progress ends. A conversion takes IT_T times
FD_IT, up to 3.2 s. Leaving shutdown starts a new one at once, so the
driver passes through shutdown on every change and waits one conversion
period plus a margin before it reads the count. The timing was measured
on a Tegra Note 7.

Tested-by: Svyatoslav Ryhel <clamor95@gmail.com> # Tegratab P1988
Signed-off-by: Patrick Fischer <admin@tsv-stahl-riesa.de>
---
 drivers/iio/light/Kconfig  |  10 ++
 drivers/iio/light/Makefile |   1 +
 drivers/iio/light/cm3217.c | 419 +++++++++++++++++++++++++++++++++++++++++++++
 3 files changed, 430 insertions(+)

diff --git a/drivers/iio/light/Kconfig b/drivers/iio/light/Kconfig
index d0dea4f3113b..451d26e6e97d 100644
--- a/drivers/iio/light/Kconfig
+++ b/drivers/iio/light/Kconfig
@@ -196,6 +196,16 @@ config BH1780
 	  To compile this driver as a module, choose M here: the module will
 	  be called bh1780.
 
+config CM3217
+	tristate "Capella CM3217 ambient light sensor"
+	depends on I2C
+	help
+	  Say Y here to build support for the Capella Microsystems CM3217
+	  ambient light sensor.
+
+	  To compile this driver as a module, choose M here: the module will
+	  be called cm3217.
+
 config CM32181
 	depends on I2C
 	tristate "CM32181 driver"
diff --git a/drivers/iio/light/Makefile b/drivers/iio/light/Makefile
index 9fc046e636a2..5daff8ef0daa 100644
--- a/drivers/iio/light/Makefile
+++ b/drivers/iio/light/Makefile
@@ -20,6 +20,7 @@ obj-$(CONFIG_AS7343)		+= as7343.o
 obj-$(CONFIG_BH1745)		+= bh1745.o
 obj-$(CONFIG_BH1750)		+= bh1750.o
 obj-$(CONFIG_BH1780)		+= bh1780.o
+obj-$(CONFIG_CM3217)		+= cm3217.o
 obj-$(CONFIG_CM32181)		+= cm32181.o
 obj-$(CONFIG_CM3232)		+= cm3232.o
 obj-$(CONFIG_CM3323)		+= cm3323.o
diff --git a/drivers/iio/light/cm3217.c b/drivers/iio/light/cm3217.c
new file mode 100644
index 000000000000..0c2c7f9d7d69
--- /dev/null
+++ b/drivers/iio/light/cm3217.c
@@ -0,0 +1,419 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Capella CM3217 ambient light sensor driver
+ *
+ * The CM3217 has no registers. It answers on two fixed I2C addresses:
+ * writing a byte to 0x10 or 0x11 sets command byte 1 or 2, reading a byte
+ * from 0x10 or 0x11 returns the MSB or LSB of the 16-bit light count.
+ *
+ * Copyright (C) 2026 Patrick Fischer <admin@tsv-stahl-riesa.de>
+ */
+
+#include <linux/array_size.h>
+#include <linux/bitfield.h>
+#include <linux/bits.h>
+#include <linux/build_bug.h>
+#include <linux/cleanup.h>
+#include <linux/delay.h>
+#include <linux/device.h>
+#include <linux/err.h>
+#include <linux/i2c.h>
+#include <linux/ktime.h>
+#include <linux/module.h>
+#include <linux/mutex.h>
+#include <linux/pm.h>
+#include <linux/property.h>
+#include <linux/regulator/consumer.h>
+#include <linux/time64.h>
+#include <linux/types.h>
+#include <linux/units.h>
+
+#include <linux/iio/iio.h>
+
+/* Second address if the firmware node does not give it */
+#define CM3217_ADDR_CMD2_LSB	0x11
+
+#define CM3217_CMD1_RSVD	BIT(5)		/* reserved, set to 1 */
+#define CM3217_CMD1_IT_T	GENMASK(3, 2)	/* 1/2 T, 1 T, 2 T, 4 T */
+#define CM3217_CMD1_WDM		BIT(1)		/* set to 1 like the vendor driver */
+#define CM3217_CMD1_SD		BIT(0)		/* shutdown when set */
+
+#define CM3217_CMD2_FD_IT	GENMASK(7, 5)
+
+#define CM3217_IT_T_2T		2
+#define CM3217_FD_IT_100MS	5
+
+/*
+ * The finest resolution is 0.01875 lux per count, at 4 T and 800 ms. The
+ * resolution is inversely proportional to IT_T and FD_IT, so keep it as
+ * nanolux per count times milliseconds.
+ */
+#define CM3217_NLUX_MS		(18750000ULL * 800)	/* 0.01875 lux * 800 ms */
+
+#define CM3217_MARGIN_MS	10
+
+/* FD_IT settings in seconds, indexed by the field value */
+static const int cm3217_int_time_avail[][2] = {
+	{ 0, 800000 }, { 0, 400000 }, { 0, 266000 }, { 0, 200000 },
+	{ 0, 130000 }, { 0, 100000 }, { 0, 80000 }, { 0, 66000 },
+};
+
+/* Split nanolux into the integer and nano parts of IIO_VAL_INT_PLUS_NANO */
+#define CM3217_NLUX_TO_VAL(nlux)	{ (nlux) / NANO, (nlux) % NANO }
+
+/* Scale in lux per count at FD_IT = ms milliseconds and IT_T = 1/2 T << it_t */
+#define CM3217_SCALE(ms, it_t) \
+	CM3217_NLUX_TO_VAL((CM3217_NLUX_MS << (3 - (it_t))) / (ms))
+
+#define CM3217_SCALES(ms) {					\
+	CM3217_SCALE(ms, 0), CM3217_SCALE(ms, 1),		\
+	CM3217_SCALE(ms, 2), CM3217_SCALE(ms, 3),		\
+}
+
+/* Available scales, indexed by FD_IT and then by IT_T */
+static const int cm3217_scale_avail[][4][2] = {
+	CM3217_SCALES(800), CM3217_SCALES(400),
+	CM3217_SCALES(266), CM3217_SCALES(200),
+	CM3217_SCALES(130), CM3217_SCALES(100),
+	CM3217_SCALES(80), CM3217_SCALES(66),
+};
+
+static_assert(ARRAY_SIZE(cm3217_scale_avail) == ARRAY_SIZE(cm3217_int_time_avail));
+
+struct cm3217_data {
+	struct i2c_client *client;
+	struct i2c_client *client_lsb;
+	/* protects the command bytes and ready */
+	struct mutex lock;
+	u8 cmd1;
+	u8 cmd2;
+	ktime_t ready;
+};
+
+static unsigned int cm3217_conv_ms(struct cm3217_data *data)
+	__must_hold(&data->lock)
+{
+	unsigned int fd_it = FIELD_GET(CM3217_CMD2_FD_IT, data->cmd2);
+	unsigned int it_t = FIELD_GET(CM3217_CMD1_IT_T, data->cmd1);
+
+	return ((cm3217_int_time_avail[fd_it][1] / USEC_PER_MSEC) << it_t) / 2;
+}
+
+static int cm3217_power_down(struct cm3217_data *data, u8 cmd1)
+{
+	return i2c_smbus_write_byte(data->client, cmd1 | CM3217_CMD1_SD);
+}
+
+/*
+ * A new setting only takes effect when the conversion in progress ends,
+ * which can take up to 3.2 s. Leaving shutdown starts a new conversion
+ * right away, so pass through shutdown on every change.
+ */
+static int cm3217_write_cmd(struct cm3217_data *data, u8 cmd1, u8 cmd2)
+	__must_hold(&data->lock)
+{
+	unsigned int conv_ms;
+	int ret;
+
+	ret = cm3217_power_down(data, cmd1);
+	if (ret)
+		return ret;
+
+	ret = i2c_smbus_write_byte(data->client_lsb, cmd2);
+	if (ret)
+		return ret;
+
+	ret = i2c_smbus_write_byte(data->client, cmd1);
+	if (ret)
+		return ret;
+
+	data->cmd1 = cmd1;
+	data->cmd2 = cmd2;
+
+	/*
+	 * The first count is ready after one conversion. The conversion time
+	 * is only the nominal one, so add 10 % and a fixed margin.
+	 */
+	conv_ms = cm3217_conv_ms(data);
+	conv_ms += conv_ms / 10 + CM3217_MARGIN_MS;
+	data->ready = ktime_add_ms(ktime_get(), conv_ms);
+
+	return 0;
+}
+
+static int cm3217_read_count(struct cm3217_data *data, int *val)
+	__must_hold(&data->lock)
+{
+	s64 wait_ms;
+	int lsb, msb;
+
+	wait_ms = ktime_ms_delta(data->ready, ktime_get());
+	if (wait_ms > 0)
+		msleep(wait_ms);
+
+	lsb = i2c_smbus_read_byte(data->client_lsb);
+	if (lsb < 0)
+		return lsb;
+
+	msb = i2c_smbus_read_byte(data->client);
+	if (msb < 0)
+		return msb;
+
+	*val = msb << 8 | lsb;
+
+	return 0;
+}
+
+static const struct iio_chan_spec cm3217_channels[] = {
+	{
+		.type = IIO_LIGHT,
+		.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_all = BIT(IIO_CHAN_INFO_INT_TIME),
+		.info_mask_shared_by_all_available = BIT(IIO_CHAN_INFO_INT_TIME),
+	},
+};
+
+static int cm3217_read_raw(struct iio_dev *indio_dev,
+			   struct iio_chan_spec const *chan,
+			   int *val, int *val2, long mask)
+{
+	struct cm3217_data *data = iio_priv(indio_dev);
+	unsigned int fd_it, it_t;
+	int ret;
+
+	guard(mutex)(&data->lock);
+
+	fd_it = FIELD_GET(CM3217_CMD2_FD_IT, data->cmd2);
+	it_t = FIELD_GET(CM3217_CMD1_IT_T, data->cmd1);
+
+	switch (mask) {
+	case IIO_CHAN_INFO_RAW:
+		ret = cm3217_read_count(data, val);
+		if (ret)
+			return ret;
+		return IIO_VAL_INT;
+	case IIO_CHAN_INFO_SCALE:
+		*val = cm3217_scale_avail[fd_it][it_t][0];
+		*val2 = cm3217_scale_avail[fd_it][it_t][1];
+		return IIO_VAL_INT_PLUS_NANO;
+	case IIO_CHAN_INFO_INT_TIME:
+		*val = cm3217_int_time_avail[fd_it][0];
+		*val2 = cm3217_int_time_avail[fd_it][1];
+		return IIO_VAL_INT_PLUS_MICRO;
+	default:
+		return -EINVAL;
+	}
+}
+
+static int cm3217_read_avail(struct iio_dev *indio_dev,
+			     struct iio_chan_spec const *chan,
+			     const int **vals, int *type, int *length,
+			     long mask)
+{
+	struct cm3217_data *data = iio_priv(indio_dev);
+	unsigned int fd_it;
+
+	switch (mask) {
+	case IIO_CHAN_INFO_SCALE:
+		scoped_guard(mutex, &data->lock)
+			fd_it = FIELD_GET(CM3217_CMD2_FD_IT, data->cmd2);
+		*vals = (const int *)cm3217_scale_avail[fd_it];
+		*length = 2 * ARRAY_SIZE(cm3217_scale_avail[0]);
+		*type = IIO_VAL_INT_PLUS_NANO;
+		return IIO_AVAIL_LIST;
+	case IIO_CHAN_INFO_INT_TIME:
+		*vals = (const int *)cm3217_int_time_avail;
+		*length = 2 * ARRAY_SIZE(cm3217_int_time_avail);
+		*type = IIO_VAL_INT_PLUS_MICRO;
+		return IIO_AVAIL_LIST;
+	default:
+		return -EINVAL;
+	}
+}
+
+static int cm3217_find_avail(const int (*avail)[2], unsigned int len,
+			     int val, int val2)
+{
+	for (unsigned int i = 0; i < len; i++) {
+		if (avail[i][0] == val && avail[i][1] == val2)
+			return i;
+	}
+
+	return -EINVAL;
+}
+
+static int cm3217_write_raw(struct iio_dev *indio_dev,
+			    struct iio_chan_spec const *chan,
+			    int val, int val2, long mask)
+{
+	struct cm3217_data *data = iio_priv(indio_dev);
+	unsigned int fd_it;
+	u8 cmd1, cmd2;
+	int i;
+
+	guard(mutex)(&data->lock);
+
+	switch (mask) {
+	case IIO_CHAN_INFO_SCALE:
+		fd_it = FIELD_GET(CM3217_CMD2_FD_IT, data->cmd2);
+		i = cm3217_find_avail(cm3217_scale_avail[fd_it],
+				      ARRAY_SIZE(cm3217_scale_avail[0]),
+				      val, val2);
+		if (i < 0)
+			return i;
+
+		cmd1 = data->cmd1;
+		FIELD_MODIFY(CM3217_CMD1_IT_T, &cmd1, i);
+
+		return cm3217_write_cmd(data, cmd1, data->cmd2);
+	case IIO_CHAN_INFO_INT_TIME:
+		i = cm3217_find_avail(cm3217_int_time_avail,
+				      ARRAY_SIZE(cm3217_int_time_avail),
+				      val, val2);
+		if (i < 0)
+			return i;
+
+		cmd2 = FIELD_PREP(CM3217_CMD2_FD_IT, i);
+
+		return cm3217_write_cmd(data, data->cmd1, cmd2);
+	default:
+		return -EINVAL;
+	}
+}
+
+static int cm3217_write_raw_get_fmt(struct iio_dev *indio_dev,
+				    struct iio_chan_spec const *chan,
+				    long mask)
+{
+	switch (mask) {
+	case IIO_CHAN_INFO_SCALE:
+		return IIO_VAL_INT_PLUS_NANO;
+	case IIO_CHAN_INFO_INT_TIME:
+		return IIO_VAL_INT_PLUS_MICRO;
+	default:
+		return -EINVAL;
+	}
+}
+
+static const struct iio_info cm3217_info = {
+	.read_raw = cm3217_read_raw,
+	.read_avail = cm3217_read_avail,
+	.write_raw = cm3217_write_raw,
+	.write_raw_get_fmt = cm3217_write_raw_get_fmt,
+};
+
+static void cm3217_power_off(void *_data)
+{
+	struct cm3217_data *data = _data;
+
+	cm3217_power_down(data, data->cmd1);
+}
+
+static int cm3217_probe(struct i2c_client *client)
+{
+	struct device *dev = &client->dev;
+	struct cm3217_data *data;
+	struct iio_dev *indio_dev;
+	u16 addr_lsb = CM3217_ADDR_CMD2_LSB;
+	u32 reg[2];
+	u8 cmd1, cmd2;
+	int ret;
+
+	indio_dev = devm_iio_device_alloc(dev, sizeof(*data));
+	if (!indio_dev)
+		return -ENOMEM;
+
+	data = iio_priv(indio_dev);
+	data->client = client;
+	i2c_set_clientdata(client, indio_dev);
+
+	ret = devm_mutex_init(dev, &data->lock);
+	if (ret)
+		return ret;
+
+	ret = devm_regulator_get_enable(dev, "vdd");
+	if (ret)
+		return dev_err_probe(dev, ret, "failed to enable vdd supply\n");
+
+	/* Without a firmware node (e.g. sysfs new_device) use the fixed one */
+	if (!device_property_read_u32_array(dev, "reg", reg, ARRAY_SIZE(reg)))
+		addr_lsb = reg[1];
+
+	data->client_lsb = devm_i2c_new_dummy_device(dev, client->adapter,
+						     addr_lsb);
+	if (IS_ERR(data->client_lsb))
+		return dev_err_probe(dev, PTR_ERR(data->client_lsb),
+				     "failed to register second address\n");
+
+	/* Start with the setting of the vendor driver: 2 T, 100 ms */
+	cmd1 = CM3217_CMD1_RSVD | CM3217_CMD1_WDM |
+	       FIELD_PREP(CM3217_CMD1_IT_T, CM3217_IT_T_2T);
+	cmd2 = FIELD_PREP(CM3217_CMD2_FD_IT, CM3217_FD_IT_100MS);
+
+	scoped_guard(mutex, &data->lock) {
+		ret = cm3217_write_cmd(data, cmd1, cmd2);
+		if (ret)
+			return dev_err_probe(dev, ret, "failed to power on\n");
+	}
+
+	ret = devm_add_action_or_reset(dev, cm3217_power_off, data);
+	if (ret)
+		return ret;
+
+	indio_dev->name = "cm3217";
+	indio_dev->info = &cm3217_info;
+	indio_dev->channels = cm3217_channels;
+	indio_dev->num_channels = ARRAY_SIZE(cm3217_channels);
+	indio_dev->modes = INDIO_DIRECT_MODE;
+
+	return devm_iio_device_register(dev, indio_dev);
+}
+
+static int cm3217_suspend(struct device *dev)
+{
+	struct cm3217_data *data = iio_priv(dev_get_drvdata(dev));
+
+	guard(mutex)(&data->lock);
+
+	return cm3217_power_down(data, data->cmd1);
+}
+
+static int cm3217_resume(struct device *dev)
+{
+	struct cm3217_data *data = iio_priv(dev_get_drvdata(dev));
+
+	guard(mutex)(&data->lock);
+
+	return cm3217_write_cmd(data, data->cmd1, data->cmd2);
+}
+
+static DEFINE_SIMPLE_DEV_PM_OPS(cm3217_pm_ops, cm3217_suspend, cm3217_resume);
+
+static const struct i2c_device_id cm3217_id[] = {
+	{ .name = "cm3217" },
+	{ }
+};
+MODULE_DEVICE_TABLE(i2c, cm3217_id);
+
+static const struct of_device_id cm3217_of_match[] = {
+	{ .compatible = "capella,cm3217" },
+	{ }
+};
+MODULE_DEVICE_TABLE(of, cm3217_of_match);
+
+static struct i2c_driver cm3217_driver = {
+	.driver = {
+		.name = "cm3217",
+		.of_match_table = cm3217_of_match,
+		.pm = pm_sleep_ptr(&cm3217_pm_ops),
+	},
+	.probe = cm3217_probe,
+	.id_table = cm3217_id,
+};
+module_i2c_driver(cm3217_driver);
+
+MODULE_AUTHOR("Patrick Fischer <admin@tsv-stahl-riesa.de>");
+MODULE_DESCRIPTION("Capella CM3217 ambient light sensor driver");
+MODULE_LICENSE("GPL");

-- 
2.56.0

Re: [PATCH v3 2/2] iio: light: Add Capella CM3217 ambient light sensor driver

[Jonathan Cameron]

On Fri, 13 Nov 2026 20:59:00 +0100
Patrick Fischer via B4 Relay <devnull+admin.tsv-stahl-riesa.de@kernel.org> wrote:

> From: Patrick Fischer <admin@tsv-stahl-riesa.de>
> 
> The CM3217 has no registers and no ID. Writing a byte to address 0x10
> or 0x11 sets command byte 1 or 2, reading a byte from 0x10 or 0x11
> returns the high or low byte of the 16-bit light count. The driver
> takes the second address from the second reg entry and falls back to
> 0x11 when there is no firmware node, as with new_device.
> 
> Command byte 1 holds the shutdown bit and the IT_T field (1/2 T, 1 T,
> 2 T or 4 T), command byte 2 the FD_IT field (800 ms down to 66 ms). The
> count scales linearly with both. The driver exposes FD_IT as the
> integration time and IT_T through the scale, so the scale list offers
> four ranges for each integration time.
> 
> The datasheet is not public. The bit fields, the reserved bits that are
> written as 1 and the startup setting of 2 T and 100 ms come from NVIDIA's
> downstream drivers (drivers/staging/iio/light/cm3217.c in the 3.4 kernel
> rel-tegranote-r8 and the 3.10 kernel
> android-tegra-flounder-3.10-nougat-mr1.1). One value differs: the vendor
> header defines 4 T as 4 << 2, which is outside the two-bit field. On a
> Tegra Note 7 field value 3 gave four times the 1 T count, so the driver
> uses that. For the resolution, Capella
> gives a range of 0.01875 to 119156 lux. The driver takes 0.01875 lux
> per count at 4 T and 800 ms. This matches both the upper end (65535
> counts at 1/2 T and 66 ms) and the 0.3 lux per count that the NVIDIA
> 3.4 driver uses at 2 T and 100 ms.
> 
> The sensor has no data-ready flag, and a new setting only takes effect
> when the conversion in progress ends. A conversion takes IT_T times
> FD_IT, up to 3.2 s. Leaving shutdown starts a new one at once, so the
> driver passes through shutdown on every change and waits one conversion
> period plus a margin before it reads the count. The timing was measured
> on a Tegra Note 7.
> 
> Tested-by: Svyatoslav Ryhel <clamor95@gmail.com> # Tegratab P1988
> Signed-off-by: Patrick Fischer <admin@tsv-stahl-riesa.de>
Hi Patrick

One small thing about how you are handling the firmware absent case.

Thanks,

Jonathan

> diff --git a/drivers/iio/light/cm3217.c b/drivers/iio/light/cm3217.c
> new file mode 100644
> index 000000000000..0c2c7f9d7d69
> --- /dev/null
> +++ b/drivers/iio/light/cm3217.c
> @@ -0,0 +1,419 @@

> +
> +static int cm3217_probe(struct i2c_client *client)
> +{
> +	struct device *dev = &client->dev;
> +	struct cm3217_data *data;
> +	struct iio_dev *indio_dev;
> +	u16 addr_lsb = CM3217_ADDR_CMD2_LSB;
> +	u32 reg[2];
> +	u8 cmd1, cmd2;
> +	int ret;
> +
> +	indio_dev = devm_iio_device_alloc(dev, sizeof(*data));
> +	if (!indio_dev)
> +		return -ENOMEM;
> +
> +	data = iio_priv(indio_dev);
> +	data->client = client;
> +	i2c_set_clientdata(client, indio_dev);
> +
> +	ret = devm_mutex_init(dev, &data->lock);
> +	if (ret)
> +		return ret;
> +
> +	ret = devm_regulator_get_enable(dev, "vdd");
> +	if (ret)
> +		return dev_err_probe(dev, ret, "failed to enable vdd supply\n");
> +
> +	/* Without a firmware node (e.g. sysfs new_device) use the fixed one */

I'd rather we handled that explicitly.

	if (dev_fwmode(dev))

That way we can return an error if there is firmware but it's broken.

> +	if (!device_property_read_u32_array(dev, "reg", reg, ARRAY_SIZE(reg)))
> +		addr_lsb = reg[1];