Re: [PATCH v2 2/2] hwmon: (pmbus) Add support for MPS Multi-phase mp5990

[Guenter Roeck]

On 11/8/23 20:48, Peter Yin wrote:
> Add support for mp5990 device from Monolithic Power Systems, Inc. (MPS)
> vendor. This is a Hot-Swap Controller.
>
> Signed-off-by: Peter Yin <peteryin.openbmc@xxxxxxxxx>
> ---
>   Documentation/hwmon/index.rst  |  1 +
>   Documentation/hwmon/mp5990.rst | 84 +++++++++++++++++++++++++++++++++
>   drivers/hwmon/pmbus/Kconfig    |  9 ++++
>   drivers/hwmon/pmbus/Makefile   |  1 +
>   drivers/hwmon/pmbus/mp5990.c   | 86 ++++++++++++++++++++++++++++++++++
>   5 files changed, 181 insertions(+)
>   create mode 100644 Documentation/hwmon/mp5990.rst
>   create mode 100644 drivers/hwmon/pmbus/mp5990.c
>
> diff --git a/Documentation/hwmon/index.rst b/Documentation/hwmon/index.rst
> index 042e1cf9501b..8c70e10fc795 100644
> --- a/Documentation/hwmon/index.rst
> +++ b/Documentation/hwmon/index.rst
> @@ -157,6 +157,7 @@ Hardware Monitoring Kernel Drivers
>      mp2888
>      mp2975
>      mp5023
> +   mp5990
>      nct6683
>      nct6775
>      nct7802
> diff --git a/Documentation/hwmon/mp5990.rst b/Documentation/hwmon/mp5990.rst
> new file mode 100644
> index 000000000000..d2da0f767530
> --- /dev/null
> +++ b/Documentation/hwmon/mp5990.rst
> @@ -0,0 +1,84 @@
> +.. SPDX-License-Identifier: GPL-2.0
> +
> +Kernel driver mp5990
> +====================
> +
> +Supported chips:
> +
> +  * MPS MP5990
> +
> +    Prefix: 'mp5990'
> +
> +  * Datasheet
> +
> +    Publicly available at the MPS website : https://www.monolithicpower.com/en/mp5990.html
> +
> +Author:
> +
> +	Peter Yin <peteryin.openbmc@xxxxxxxxx>
> +
> +Description
> +-----------
> +
> +This driver implements support for Monolithic Power Systems, Inc. (MPS)
> +MP5990 Hot-Swap Controller.
> +
> +Device compliant with:
> +
> +- PMBus rev 1.3 interface.
> +
> +Device supports direct format for reading input voltage, output voltage,
> +output current, input power and temperature.
> +

The device also supports linear mode according to its datasheet.

> +The driver exports the following attributes via the 'sysfs' files
> +for input voltage:
> +
> +**in1_input**
> +
> +**in1_label**
> +
> +**in1_max**
> +
> +**in1_max_alarm**
> +
> +**in1_min**
> +
> +**in1_min_alarm**
> +
> +The driver provides the following attributes for output voltage:
> +
> +**in2_input**
> +
> +**in2_label**
> +
> +**in2_alarm**
> +
> +The driver provides the following attributes for output current:
> +
> +**curr1_input**
> +
> +**curr1_label**
> +
> +**curr1_alarm**
> +
> +**curr1_max**
> +
> +The driver provides the following attributes for input power:
> +
> +**power1_input**
> +
> +**power1_label**
> +
> +**power1_alarm**
> +
> +The driver provides the following attributes for temperature:
> +
> +**temp1_input**
> +
> +**temp1_max**
> +
> +**temp1_max_alarm**
> +
> +**temp1_crit**
> +
> +**temp1_crit_alarm**
> diff --git a/drivers/hwmon/pmbus/Kconfig b/drivers/hwmon/pmbus/Kconfig
> index 270b6336b76d..65a116f7744d 100644
> --- a/drivers/hwmon/pmbus/Kconfig
> +++ b/drivers/hwmon/pmbus/Kconfig
> @@ -326,6 +326,15 @@ config SENSORS_MP5023
>   	  This driver can also be built as a module. If so, the module will
>   	  be called mp5023.
>   
> +config SENSORS_MP5990
> +	tristate "MPS MP5990"
> +	help
> +	  If you say yes here you get hardware monitoring support for MPS
> +	  MP5990.
> +
> +	  This driver can also be built as a module. If so, the module will
> +	  be called mp5990.
> +
>   config SENSORS_MPQ7932_REGULATOR
>   	bool "Regulator support for MPQ7932"
>   	depends on SENSORS_MPQ7932 && REGULATOR
> diff --git a/drivers/hwmon/pmbus/Makefile b/drivers/hwmon/pmbus/Makefile
> index 84ee960a6c2d..212d9ca0acc9 100644
> --- a/drivers/hwmon/pmbus/Makefile
> +++ b/drivers/hwmon/pmbus/Makefile
> @@ -35,6 +35,7 @@ obj-$(CONFIG_SENSORS_MAX8688)	+= max8688.o
>   obj-$(CONFIG_SENSORS_MP2888)	+= mp2888.o
>   obj-$(CONFIG_SENSORS_MP2975)	+= mp2975.o
>   obj-$(CONFIG_SENSORS_MP5023)	+= mp5023.o
> +obj-$(CONFIG_SENSORS_MP5990)	+= mp5990.o
>   obj-$(CONFIG_SENSORS_MPQ7932)	+= mpq7932.o
>   obj-$(CONFIG_SENSORS_PLI1209BC)	+= pli1209bc.o
>   obj-$(CONFIG_SENSORS_PM6764TR)	+= pm6764tr.o
> diff --git a/drivers/hwmon/pmbus/mp5990.c b/drivers/hwmon/pmbus/mp5990.c
> new file mode 100644
> index 000000000000..fb3ac9c5d44e
> --- /dev/null
> +++ b/drivers/hwmon/pmbus/mp5990.c
> @@ -0,0 +1,86 @@
> +// SPDX-License-Identifier: GPL-2.0-or-later
> +/*
> + * Driver for MPS MP5990 Hot-Swap Controller
> + */
> +
> +#include <linux/i2c.h>
> +#include <linux/module.h>
> +#include <linux/of_device.h>
> +#include <linux/pmbus.h>

Not used in this driver.

> +#include "pmbus.h"
> +
> +static int mp5990_read_byte_data(struct i2c_client *client, int page, int reg)
> +{
> +	switch (reg) {
> +	case PMBUS_VOUT_MODE:
> +		/* The datasheet does not support the VOUT command,

Standard multi-line comments, please. This is not the networking subsystem.

> +		 * but the device responds with a default value of 0x17.
> +		 * In the standard, 0x17 represents linear mode. However,
> +		 * for the MP5990, the VOUT linear mode is linear11, not linear16.
> +		 * Therefore, we should enforce the VOUT in the direct format.
> +		 */
> +		return PB_VOUT_MODE_DIRECT;

This doesn't take into account that the reporting mode is set in
EFUSE_CFG bit 9 (RPT_FORMAT). If the chip is configured to report its data
in linear mode, all readings will be wrong if the exponent is != 0 and
for negative values.

The driver could enforce direct mode by explicitly configuring EFUSE_CFG,
but that is not guaranteed to work because the chip could be write
protected. It would be necessary to disable write protection first,
making this a bit complicated. Alternatively, the reading of VOUT could
be adjusted in linear mode to linear16 if the chip is configured to
report data in linear mode. I would personally prefer this solution.
Either case, this needs to be handled.

Guenter