Re: [PATCH 2/2] hwmon: add MP2985 driver

[Guenter Roeck]

On Mon, Mar 09, 2026 at 05:02:15PM +0800, wenswang@xxxxxxxx wrote:
> From: Wensheng Wang <wenswang@xxxxxxxx>
> 
> Add support for MPS mp2985 controller. This driver exposes
> telemetry and limit value readings and writtings.
> 
> Signed-off-by: Wensheng Wang <wenswang@xxxxxxxx>
> ---
>  Documentation/hwmon/index.rst  |   1 +
>  Documentation/hwmon/mp2985.rst | 151 ++++++++++++++
>  MAINTAINERS                    |   7 +
>  drivers/hwmon/pmbus/Kconfig    |   9 +
>  drivers/hwmon/pmbus/Makefile   |   1 +
>  drivers/hwmon/pmbus/mp2985.c   | 355 +++++++++++++++++++++++++++++++++
>  6 files changed, 524 insertions(+)
>  create mode 100644 Documentation/hwmon/mp2985.rst
>  create mode 100644 drivers/hwmon/pmbus/mp2985.c
> 
> diff --git a/Documentation/hwmon/index.rst b/Documentation/hwmon/index.rst
> index b2ca8513cfcd..1b7007f41b39 100644
> --- a/Documentation/hwmon/index.rst
> +++ b/Documentation/hwmon/index.rst
> @@ -183,6 +183,7 @@ Hardware Monitoring Kernel Drivers
>     mp2925
>     mp29502
>     mp2975
> +   mp2985
>     mp2993
>     mp5023
>     mp5920
> diff --git a/Documentation/hwmon/mp2985.rst b/Documentation/hwmon/mp2985.rst
> new file mode 100644
> index 000000000000..892c5b5ca19c
> --- /dev/null
> +++ b/Documentation/hwmon/mp2985.rst
> @@ -0,0 +1,151 @@
> +.. SPDX-License-Identifier: GPL-2.0
> +
> +Kernel driver mp2985
> +====================
> +
> +Supported chips:
> +
> +  * MPS mp2985
> +
> +    Prefix: 'mp2985'
> +
> +  * MPS mp2985
> +
> +    Prefix: 'mp2985'
> +

Duplicate entry

> +Author:
> +
> +	Wensheng Wang <wenswang@xxxxxxxx>
> +
> +Description
> +-----------
> +
> +This driver implements support for Monolithic Power Systems, Inc. (MPS)
> +MP2985 Dual Loop Digital Multi-phase Controller.
> +
> +Device compliant with:
> +
> +- PMBus rev 1.3 interface.
> +
> +The driver exports the following attributes via the 'sysfs' files
> +for input voltage:
> +
> +**in1_input**
> +
> +**in1_label**
> +
> +**in1_crit**
> +
> +**in1_crit_alarm**
> +
> +**in1_lcrit**
> +
> +**in1_lcrit_alarm**
> +
> +**in1_max**
> +
> +**in1_max_alarm**
> +
> +**in1_min**
> +
> +**in1_min_alarm**
> +
> +The driver provides the following attributes for output voltage:
> +
> +**in2_input**
> +
> +**in2_label**
> +
> +**in2_crit**
> +
> +**in2_crit_alarm**
> +
> +**in2_lcrit**
> +
> +**in2_lcrit_alarm**
> +
> +**in3_input**
> +
> +**in3_label**
> +
> +**in3_crit**
> +
> +**in3_crit_alarm**
> +
> +**in3_lcrit**
> +
> +**in3_lcrit_alarm**
> +
> +The driver provides the following attributes for input current:
> +
> +**curr1_input**
> +
> +**curr1_label**
> +
> +The driver provides the following attributes for output current:
> +
> +**curr2_input**
> +
> +**curr2_label**
> +
> +**curr2_crit**
> +
> +**curr2_crit_alarm**
> +
> +**curr2_max**
> +
> +**curr2_max_alarm**
> +
> +**curr3_input**
> +
> +**curr3_label**
> +
> +**curr3_crit**
> +
> +**curr3_crit_alarm**
> +
> +**curr3_max**
> +
> +**curr3_max_alarm**
> +
> +The driver provides the following attributes for input power:
> +
> +**power1_input**
> +
> +**power1_label**
> +
> +**power2_input**
> +
> +**power2_label**
> +
> +The driver provides the following attributes for output power:
> +
> +**power3_input**
> +
> +**power3_label**
> +
> +**power4_input**
> +
> +**power4_label**
> +
> +The driver provides the following attributes for temperature:
> +
> +**temp1_input**
> +
> +**temp1_crit**
> +
> +**temp1_crit_alarm**
> +
> +**temp1_max**
> +
> +**temp1_max_alarm**
> +
> +**temp2_input**
> +
> +**temp2_crit**
> +
> +**temp2_crit_alarm**
> +
> +**temp2_max**
> +
> +**temp2_max_alarm**
> diff --git a/MAINTAINERS b/MAINTAINERS
> index 77fdfcb55f06..7b47e31ee7a3 100644
> --- a/MAINTAINERS
> +++ b/MAINTAINERS
> @@ -17922,6 +17922,13 @@ S:	Maintained
>  F:	Documentation/hwmon/mp29502.rst
>  F:	drivers/hwmon/pmbus/mp29502.c
>  
> +MPS MP2985 DRIVER
> +M:	Wensheng Wang <wenswang@xxxxxxxx>
> +L:	linux-hwmon@xxxxxxxxxxxxxxx
> +S:	Maintained
> +F:	Documentation/hwmon/mp2985.rst
> +F:	drivers/hwmon/pmbus/mp2985.c
> +
>  MPS MP2993 DRIVER
>  M:	Noah Wang <noahwang.wang@xxxxxxxxxxx>
>  L:	linux-hwmon@xxxxxxxxxxxxxxx
> diff --git a/drivers/hwmon/pmbus/Kconfig b/drivers/hwmon/pmbus/Kconfig
> index fc1273abe357..83fe5866c083 100644
> --- a/drivers/hwmon/pmbus/Kconfig
> +++ b/drivers/hwmon/pmbus/Kconfig
> @@ -447,6 +447,15 @@ config SENSORS_MP2975
>  	  This driver can also be built as a module. If so, the module will
>  	  be called mp2975.
>  
> +config SENSORS_MP2985
> +	tristate "MPS MP2985"
> +	help
> +	  If you say yes here you get hardware monitoring support for MPS
> +	  MP2985 Dual Loop Digital Multi-Phase Controller.
> +
> +	  This driver can also be built as a module. If so, the module will
> +	  be called mp2985.
> +
>  config SENSORS_MP2993
>  	tristate "MPS MP2993"
>  	help
> diff --git a/drivers/hwmon/pmbus/Makefile b/drivers/hwmon/pmbus/Makefile
> index d6c86924f887..24505bbee2b0 100644
> --- a/drivers/hwmon/pmbus/Makefile
> +++ b/drivers/hwmon/pmbus/Makefile
> @@ -45,6 +45,7 @@ obj-$(CONFIG_SENSORS_MP2891)	+= mp2891.o
>  obj-$(CONFIG_SENSORS_MP2925)	+= mp2925.o
>  obj-$(CONFIG_SENSORS_MP29502)	+= mp29502.o
>  obj-$(CONFIG_SENSORS_MP2975)	+= mp2975.o
> +obj-$(CONFIG_SENSORS_MP2985)	+= mp2985.o
>  obj-$(CONFIG_SENSORS_MP2993)	+= mp2993.o
>  obj-$(CONFIG_SENSORS_MP5023)	+= mp5023.o
>  obj-$(CONFIG_SENSORS_MP5920)	+= mp5920.o
> diff --git a/drivers/hwmon/pmbus/mp2985.c b/drivers/hwmon/pmbus/mp2985.c
> new file mode 100644
> index 000000000000..b96c1096d294
> --- /dev/null
> +++ b/drivers/hwmon/pmbus/mp2985.c
> @@ -0,0 +1,355 @@
> +// SPDX-License-Identifier: GPL-2.0-or-later
> +/*
> + * Hardware monitoring driver for MPS Multi-phase Digital VR Controllers(MP2985)
> + *
> + * Copyright (C) 2026 MPS
> + */
> +
> +#include <linux/bitfield.h>
> +#include <linux/i2c.h>
> +#include <linux/module.h>
> +#include <linux/of_device.h>
> +#include "pmbus.h"
> +
> +/*
> + * Vender specific register READ_PIN_EST(0x93), READ_IIN_EST(0x8E),
> + * MFR_VR_MULTI_CONFIG_R1(0x0D) and MFR_VR_MULTI_CONFIG_R2(0x1D).
> + * The READ_PIN_EST is used to read pin telemetry, the READ_IIN_EST
> + * is used to read iin telemetry and the MFR_VR_MULTI_CONFIG_R1,
> + * MFR_VR_MULTI_CONFIG_R2 are used to obtain vid scale.
> + */
> +#define READ_PIN_EST	0x93
> +#define READ_IIN_EST	0x8E
> +#define MFR_VR_MULTI_CONFIG_R1	0x0D
> +#define MFR_VR_MULTI_CONFIG_R2	0x1D
> +
> +#define MP2985_VOUT_DIV	512
> +#define MP2985_VOUT_OVUV_UINT	195
> +#define MP2985_VOUT_OVUV_DIV	100
> +
> +#define MP2985_PAGE_NUM	2
> +
> +#define MP2985_RAIL1_FUNC	(PMBUS_HAVE_VIN | PMBUS_HAVE_PIN | \
> +							 PMBUS_HAVE_VOUT | PMBUS_HAVE_IOUT | \
> +							 PMBUS_HAVE_POUT | PMBUS_HAVE_TEMP | \
> +							 PMBUS_HAVE_STATUS_VOUT | \
> +							 PMBUS_HAVE_STATUS_IOUT | \
> +							 PMBUS_HAVE_STATUS_TEMP | \
> +							 PMBUS_HAVE_STATUS_INPUT)
> +
> +#define MP2985_RAIL2_FUNC	(PMBUS_HAVE_PIN | PMBUS_HAVE_VOUT | \
> +							 PMBUS_HAVE_IOUT | PMBUS_HAVE_POUT | \
> +							 PMBUS_HAVE_TEMP | PMBUS_HAVE_IIN | \
> +							 PMBUS_HAVE_STATUS_VOUT | \
> +							 PMBUS_HAVE_STATUS_IOUT | \
> +							 PMBUS_HAVE_STATUS_TEMP | \
> +							 PMBUS_HAVE_STATUS_INPUT)
> +
> +struct mp2985_data {
> +	struct pmbus_driver_info info;
> +	int vout_scale[MP2985_PAGE_NUM];
> +	int vid_offset[MP2985_PAGE_NUM];
> +};
> +
> +#define to_mp2985_data(x) container_of(x, struct mp2985_data, info)
> +
> +static u16 mp2985_linear_exp_transfer(u16 word, u16 expect_exponent)
> +{
> +	s16 exponent, mantissa, target_exponent;
> +
> +	exponent = ((s16)word) >> 11;
> +	mantissa = ((s16)((word & 0x7ff) << 5)) >> 5;
> +	target_exponent = (s16)((expect_exponent & 0x1f) << 11) >> 11;
> +
> +	if (exponent > target_exponent)
> +		mantissa = mantissa << (exponent - target_exponent);
> +	else
> +		mantissa = mantissa >> (target_exponent - exponent);
> +
> +	return (mantissa & 0x7ff) | ((expect_exponent << 11) & 0xf800);
> +}
> +
> +static int mp2985_read_byte_data(struct i2c_client *client, int page, int reg)
> +{
> +	int ret;
> +
> +	switch (reg) {
> +	case PMBUS_VOUT_MODE:
> +		/*
> +		 * The MP2985 does not follow standard PMBus protocol completely,
> +		 * and the calculation of vout in this driver is based on direct
> +		 * format. As a result, the format of vout is enforced to direct.
> +		 */
> +		ret = PB_VOUT_MODE_DIRECT;
> +		break;
> +	default:
> +		ret = -ENODATA;
> +		break;
> +	}
> +
> +	return ret;
> +}
> +
> +static int mp2985_read_word_data(struct i2c_client *client, int page, int phase,
> +				 int reg)
> +{
> +	const struct pmbus_driver_info *info = pmbus_get_driver_info(client);
> +	struct mp2985_data *data = to_mp2985_data(info);
> +	int ret;
> +
> +	switch (reg) {
> +	case PMBUS_READ_VOUT:
> +		ret = pmbus_read_word_data(client, page, phase, reg);
> +		if (ret < 0)
> +			return ret;
> +
> +		/*
> +		 * In vid mode, the MP2985 vout telemetry has 49 vid step offset, but
> +		 * PMBUS_VOUT_OV_FAULT_LIMIT and PMBUS_VOUT_UV_FAULT_LIMIT do not take
> +		 * this into consideration, its resolution is 1.95mV/LSB, as a result,
> +		 * format[PSC_VOLTAGE_OUT] can not be set to vid directly. Adding extra
> +		 * vid_offset variable for vout telemetry.
> +		 */

This is a bit misleading, since the code (appears to) cover both VID and
non-VID mode. The complete set of supported modes needs to be explained
somewhere.

> +		ret = DIV_ROUND_CLOSEST(((ret & GENMASK(11, 0)) + data->vid_offset[page]) *
> +					data->vout_scale[page], MP2985_VOUT_DIV);

Based on the code below, vout_scale can be 5,120, and vid_offset can be 49.
That means the maximum value of "ret" can be
	(4,095 + 49) * 5,120 / 512, or 41,440

If the result exceeds 32,767, the calling code will interpret this as
negative value. It should be clamped to 32,767 to ensure that this does
not happen.

> +		break;
> +	case PMBUS_READ_IIN:
> +		/*
> +		 * The MP2985 has standard PMBUS_READ_IIN register(0x89), but this is
> +		 * not used to read the input current of per rail. The input current
> +		 * is read through the vender redefined register READ_IIN_EST(0x8E).
> +		 */
> +		ret = pmbus_read_word_data(client, page, phase, READ_IIN_EST);
> +		break;
> +	case PMBUS_READ_PIN:
> +		/*
> +		 * The MP2985 has standard PMBUS_READ_PIN register(0x97), but this
> +		 * is not used to read the input power of per rail. The input power
> +		 * of per rail is read through the vender redefined register
> +		 * READ_PIN_EST(0x93).
> +		 */
> +		ret = pmbus_read_word_data(client, page, phase, READ_PIN_EST);
> +		break;
> +	case PMBUS_VOUT_OV_FAULT_LIMIT:
> +	case PMBUS_VOUT_UV_FAULT_LIMIT:
> +		ret = pmbus_read_word_data(client, page, phase, reg);
> +		if (ret < 0)
> +			return ret;
> +
> +		ret = DIV_ROUND_CLOSEST((ret & GENMASK(11, 0)) * MP2985_VOUT_OVUV_UINT,
> +					MP2985_VOUT_OVUV_DIV);
> +		break;
> +	case PMBUS_STATUS_WORD:
> +	case PMBUS_READ_VIN:
> +	case PMBUS_READ_IOUT:
> +	case PMBUS_READ_POUT:
> +	case PMBUS_READ_TEMPERATURE_1:
> +	case PMBUS_VIN_OV_FAULT_LIMIT:
> +	case PMBUS_VIN_OV_WARN_LIMIT:
> +	case PMBUS_VIN_UV_WARN_LIMIT:
> +	case PMBUS_VIN_UV_FAULT_LIMIT:
> +	case PMBUS_IOUT_OC_FAULT_LIMIT:
> +	case PMBUS_IOUT_OC_WARN_LIMIT:
> +	case PMBUS_OT_FAULT_LIMIT:
> +	case PMBUS_OT_WARN_LIMIT:
> +		ret = -ENODATA;
> +		break;
> +	default:
> +		ret = -EINVAL;
> +		break;
> +	}
> +
> +	return ret;
> +}
> +
> +static int mp2985_write_word_data(struct i2c_client *client, int page, int reg,
> +				  u16 word)
> +{
> +	int ret;
> +
> +	switch (reg) {
> +	case PMBUS_VIN_OV_FAULT_LIMIT:
> +	case PMBUS_VIN_OV_WARN_LIMIT:
> +	case PMBUS_VIN_UV_WARN_LIMIT:
> +	case PMBUS_VIN_UV_FAULT_LIMIT:
> +		/*
> +		 * The PMBUS_VIN_OV_FAULT_LIMIT, PMBUS_VIN_OV_WARN_LIMIT,
> +		 * PMBUS_VIN_UV_WARN_LIMIT and PMBUS_VIN_UV_FAULT_LIMIT
> +		 * of MP2985 is linear11 format, and the exponent is a
> +		 * constant value(5'b11101)， so the exponent of word
> +		 * parameter should be converted to 5'b11101(0x1D).
> +		 */
> +		ret = pmbus_write_word_data(client, page, reg,
> +					    mp2985_linear_exp_transfer(word, 0x1D));
> +		break;
> +	case PMBUS_VOUT_OV_FAULT_LIMIT:
> +	case PMBUS_VOUT_UV_FAULT_LIMIT:
> +		/*
> +		 * The bit0-bit11 is the limit value, and bit12-bit15
> +		 * should not be changed.
> +		 */
> +		ret = pmbus_read_word_data(client, page, 0xff, reg);
> +		if (ret < 0)
> +			return ret;
> +
> +		ret = pmbus_write_word_data(client, page, reg,
> +					    (ret & ~GENMASK(11, 0)) |
> +				FIELD_PREP(GENMASK(11, 0),
> +					   DIV_ROUND_CLOSEST(word * MP2985_VOUT_OVUV_DIV,
> +							     MP2985_VOUT_OVUV_UINT)));
> +		break;
> +	case PMBUS_OT_FAULT_LIMIT:
> +	case PMBUS_OT_WARN_LIMIT:
> +		/*
> +		 * The PMBUS_OT_FAULT_LIMIT and PMBUS_OT_WARN_LIMIT of
> +		 * MP2985 is linear11 format, and the exponent is a
> +		 * constant value(5'b00000), so the exponent of word
> +		 * parameter should be converted to 5'b00000.
> +		 */
> +		ret = pmbus_write_word_data(client, page, reg,
> +					    mp2985_linear_exp_transfer(word, 0x00));
> +		break;
> +	case PMBUS_IOUT_OC_FAULT_LIMIT:
> +	case PMBUS_IOUT_OC_WARN_LIMIT:
> +		/*
> +		 * The PMBUS_IOUT_OC_FAULT_LIMIT and PMBUS_IOUT_OC_WARN_LIMIT
> +		 * of MP2985 is linear11 format, and the exponent can not be
> +		 * changed.
> +		 */
> +		ret = pmbus_read_word_data(client, page, 0xff, reg);
> +		if (ret < 0)
> +			return ret;
> +
> +		ret = pmbus_write_word_data(client, page, reg,
> +					    mp2985_linear_exp_transfer(word,
> +								       FIELD_GET(GENMASK(15, 11),
> +										 ret)));
> +		break;
> +	default:
> +		ret = -EINVAL;
> +		break;
> +	}
> +
> +	return ret;
> +}
> +
> +static int
> +mp2985_identify_vout_scale(struct i2c_client *client, struct pmbus_driver_info *info,
> +			   int page)
> +{
> +	struct mp2985_data *data = to_mp2985_data(info);
> +	int ret;
> +
> +	ret = i2c_smbus_write_byte_data(client, PMBUS_PAGE, page);
> +	if (ret < 0)
> +		return ret;
> +
> +	ret = i2c_smbus_read_byte_data(client, PMBUS_VOUT_MODE);
> +	if (ret < 0)
> +		return ret;
> +
> +	if (FIELD_GET(GENMASK(5, 5), ret)) {

This is just BIT(5), isn't it ? Why the complexity ?

> +		ret = i2c_smbus_write_byte_data(client, PMBUS_PAGE, 2);
> +		if (ret < 0)
> +			return ret;

This will leave the chip on page 2, which may confuse the PMBus core.

> +
> +		ret = i2c_smbus_read_word_data(client, page == 0 ?
> +									MFR_VR_MULTI_CONFIG_R1 :
> +									MFR_VR_MULTI_CONFIG_R2);

Return value is not checked.

Alignment is completely off here.

> +
> +		if (page == 0) {
> +			if (FIELD_GET(GENMASK(4, 4), ret))

Same here and everywhere else where the same logic is used.

> +				data->vout_scale[page] = 2560;
> +			else
> +				data->vout_scale[page] = 5120;
> +		} else {
> +			if (FIELD_GET(GENMASK(3, 3), ret))
> +				data->vout_scale[page] = 2560;
> +			else
> +				data->vout_scale[page] = 5120;
> +		}
> +
> +		data->vid_offset[page] = 49;
> +	} else if (FIELD_GET(GENMASK(4, 4), ret)) {
> +		data->vout_scale[page] = 1;
> +		data->vid_offset[page] = 0;
> +	} else {
> +		data->vout_scale[page] = 512;
> +		data->vid_offset[page] = 0;
> +	}

The context suggests that bit 5 and bit 4 may refer to different input modes.
There should be a comment explaining what is what.

> +
> +	return 0;
> +}
> +
> +static int mp2985_identify(struct i2c_client *client, struct pmbus_driver_info *info)
> +{
> +	int ret;
> +
> +	ret = mp2985_identify_vout_scale(client, info, 0);
> +	if (ret < 0)
> +		return ret;
> +
> +	return mp2985_identify_vout_scale(client, info, 1);
> +}
> +
> +static struct pmbus_driver_info mp2985_info = {
> +	.pages = MP2985_PAGE_NUM,
> +	.format[PSC_VOLTAGE_IN] = linear,
> +	.format[PSC_CURRENT_IN] = linear,
> +	.format[PSC_CURRENT_OUT] = linear,
> +	.format[PSC_POWER] = linear,
> +	.format[PSC_TEMPERATURE] = linear,
> +	.format[PSC_VOLTAGE_OUT] = direct,
> +
> +	.m[PSC_VOLTAGE_OUT] = 1,
> +	.R[PSC_VOLTAGE_OUT] = 3,
> +	.b[PSC_VOLTAGE_OUT] = 0,
> +
> +	.func[0] = MP2985_RAIL1_FUNC,
> +	.func[1] = MP2985_RAIL2_FUNC,
> +	.read_word_data = mp2985_read_word_data,
> +	.read_byte_data = mp2985_read_byte_data,
> +	.write_word_data = mp2985_write_word_data,
> +	.identify = mp2985_identify,
> +};
> +
> +static int mp2985_probe(struct i2c_client *client)
> +{
> +	struct mp2985_data *data;
> +
> +	data = devm_kzalloc(&client->dev, sizeof(struct mp2985_data), GFP_KERNEL);
> +	if (!data)
> +		return -ENOMEM;
> +
> +	memcpy(&data->info, &mp2985_info, sizeof(mp2985_info));
> +
> +	return pmbus_do_probe(client, &data->info);
> +}
> +
> +static const struct i2c_device_id mp2985_id[] = {
> +	{"mp2985", 0},
> +	{}
> +};
> +MODULE_DEVICE_TABLE(i2c, mp2985_id);
> +
> +static const struct of_device_id __maybe_unused mp2985_of_match[] = {
> +	{.compatible = "mps,mp2985"},
> +	{}
> +};
> +MODULE_DEVICE_TABLE(of, mp2985_of_match);
> +
> +static struct i2c_driver mp2985_driver = {
> +	.driver = {
> +		.name = "mp2985",
> +		.of_match_table = mp2985_of_match,
> +	},
> +	.probe = mp2985_probe,
> +	.id_table = mp2985_id,
> +};
> +
> +module_i2c_driver(mp2985_driver);
> +
> +MODULE_AUTHOR("Wensheng Wang <wenswang@xxxxxxxx>");
> +MODULE_DESCRIPTION("PMBus driver for MPS MP2985 device");
> +MODULE_LICENSE("GPL");
> +MODULE_IMPORT_NS("PMBUS");