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Date: Tue, 30 Jan 2024 22:12:07 -0800
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Subject: Re: [PATCH v3 1/2] hwmon: Add driver for MPS MPQ8785 Synchronous
 Step-Down Converter
Content-Language: en-US
To: Charles Hsu <ythsu0511@gmail.com>, jdelvare@suse.com, corbet@lwn.net,
 Delphine_CC_Chiu@Wiwynn.com, robh+dt@kernel.org,
 krzysztof.kozlowski+dt@linaro.org, conor+dt@kernel.org,
 linux-hwmon@vger.kernel.org, devicetree@vger.kernel.org,
 linux-kernel@vger.kernel.org
References: <20240131055526.2700452-1-ythsu0511@gmail.com>
From: Guenter Roeck <linux@roeck-us.net>
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In-Reply-To: <20240131055526.2700452-1-ythsu0511@gmail.com>
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On 1/30/24 21:55, Charles Hsu wrote:
> Add support for mpq8785 device from Monolithic Power Systems, Inc.
> (MPS) vendor. This is synchronous step-down controller.
> 
> Signed-off-by: Charles Hsu <ythsu0511@gmail.com>
> 
> ---
> Change in v1:
>      Initial patchset.
> Change in v2:
>      1.Add pmbus support status registers.
>      2.Add mpq8785 in trivial-devices.yaml.
>      3.Remove format[PSC_VOLTAGE_OUT].
>      4.Fix MODULE_DESCRIPTION.
> Change in v3:
>      1.Identify vout_mode.
>      2.Separate dt-binding.
> ---
>   Documentation/hwmon/index.rst   |  1 +
>   Documentation/hwmon/mpq8785.rst | 94 +++++++++++++++++++++++++++++++++
>   drivers/hwmon/pmbus/Kconfig     |  9 ++++
>   drivers/hwmon/pmbus/Makefile    |  1 +
>   drivers/hwmon/pmbus/mpq8785.c   | 91 +++++++++++++++++++++++++++++++
>   5 files changed, 196 insertions(+)
>   create mode 100644 Documentation/hwmon/mpq8785.rst
>   create mode 100644 drivers/hwmon/pmbus/mpq8785.c
> 
> diff --git a/Documentation/hwmon/index.rst b/Documentation/hwmon/index.rst
> index c7ed1f73ac06..085ad6ca9b05 100644
> --- a/Documentation/hwmon/index.rst
> +++ b/Documentation/hwmon/index.rst
> @@ -163,6 +163,7 @@ Hardware Monitoring Kernel Drivers
>      mp2975
>      mp5023
>      mp5990
> +   mpq8785
>      nct6683
>      nct6775
>      nct7802
> diff --git a/Documentation/hwmon/mpq8785.rst b/Documentation/hwmon/mpq8785.rst
> new file mode 100644
> index 000000000000..bf8176b87086
> --- /dev/null
> +++ b/Documentation/hwmon/mpq8785.rst
> @@ -0,0 +1,94 @@
> +.. SPDX-License-Identifier: GPL-2.0-only
> +
> +Kernel driver mpq8785
> +=======================
> +
> +Supported chips:
> +
> +  * MPS MPQ8785
> +
> +    Prefix: 'mpq8785'
> +
> +Author: Charles Hsu <ythsu0511@gmail.com>
> +
> +Description
> +-----------
> +
> +The MPQ8785 is a fully integrated, PMBus-compatible, high-frequency, synchronous
> +buck converter. The MPQ8785 offers a very compact solution that achieves up to
> +40A output current per phase, with excellent load and line regulation over a
> +wide input supply range. The MPQ8785 operates at high efficiency over a wide
> +output current load range.
> +
> +The PMBus interface provides converter configurations and key parameters
> +monitoring.
> +
> +The MPQ8785 adopts MPS's proprietary multi-phase digital constant-on-time (MCOT)
> +control, which provides fast transient response and eases loop stabilization.
> +The MCOT scheme also allows multiple MPQ8785 devices to be connected in parallel
> +with excellent current sharing and phase interleaving for high-current
> +applications.
> +
> +Fully integrated protection features include over-current protection (OCP),
> +over-voltage protection (OVP), under-voltage protection (UVP), and
> +over-temperature protection (OTP).
> +
> +The MPQ8785 requires a minimal number of readily available, standard external
> +components, and is available in a TLGA (5mmx6mm) package.
> +
> +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_max**
> +
> +**in1_max_alarm**
> +
> +**in1_min**
> +
> +**in1_min_alarm**
> +
> +**in1_crit**
> +
> +**in1_crit_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_max**
> +
> +**curr1_max_alarm**
> +
> +**curr1_crit**
> +
> +**curr1_crit_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 294808f5240a..557ae0c414b0 100644
> --- a/drivers/hwmon/pmbus/Kconfig
> +++ b/drivers/hwmon/pmbus/Kconfig
> @@ -377,6 +377,15 @@ config SENSORS_MPQ7932
>   	  This driver can also be built as a module. If so, the module will
>   	  be called mpq7932.
>   
> +config SENSORS_MPQ8785
> +	tristate "MPS MPQ8785"
> +	help
> +	  If you say yes here you get hardware monitoring functionality support
> +	  for power management IC MPS MPQ8785.
> +
> +	  This driver can also be built as a module. If so, the module will
> +	  be called mpq8785.
> +
>   config SENSORS_PIM4328
>   	tristate "Flex PIM4328 and compatibles"
>   	help
> diff --git a/drivers/hwmon/pmbus/Makefile b/drivers/hwmon/pmbus/Makefile
> index cf8a76744545..f14ecf03ad77 100644
> --- a/drivers/hwmon/pmbus/Makefile
> +++ b/drivers/hwmon/pmbus/Makefile
> @@ -39,6 +39,7 @@ 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-$(CONFIG_SENSORS_MPQ8785)	+= mpq8785.o
>   obj-$(CONFIG_SENSORS_PLI1209BC)	+= pli1209bc.o
>   obj-$(CONFIG_SENSORS_PM6764TR)	+= pm6764tr.o
>   obj-$(CONFIG_SENSORS_PXE1610)	+= pxe1610.o
> diff --git a/drivers/hwmon/pmbus/mpq8785.c b/drivers/hwmon/pmbus/mpq8785.c
> new file mode 100644
> index 000000000000..b5bfc5d8a96b
> --- /dev/null
> +++ b/drivers/hwmon/pmbus/mpq8785.c
> @@ -0,0 +1,91 @@
> +// SPDX-License-Identifier: GPL-2.0-or-later
> +/*
> + * Driver for MPS MPQ8785 Step-Down Converter
> + */
> +
> +#include <linux/i2c.h>
> +#include <linux/module.h>
> +#include <linux/of_device.h>
> +#include "pmbus.h"
> +
> +static int mpq8785_identify(struct i2c_client *client,
> +			    struct pmbus_driver_info *info)
> +{
> +	int vout_mode;
> +
> +	vout_mode = pmbus_read_byte_data(client, 0, PMBUS_VOUT_MODE);

Excellent solution, but it will have to return an error if reading
VOUT_MODE fails. Something like:

	vout_mode = ...;
	if (vout_mode < 0 || vout_mode == 0xff)
		return vout_mode < 0 ? vout_mode : -ENODEV;

	switch (vout_mode >> 5) {
	...

The output mode _has_ to be valid.

Thanks,
Guenter