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Date:   Tue, 31 Mar 2020 08:46:30 -0700
From:   Guenter Roeck <linux@roeck-us.net>
To:     Kun Yi <kunyi@google.com>
Cc:     jdelvare@suse.com, robh+dt@kernel.org, mark.rutland@arm.com,
        openbmc@lists.ozlabs.org, joel@jms.id.au,
        linux-hwmon@vger.kernel.org, devicetree@vger.kernel.org,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH linux hwmon-next v2 1/3] hwmon: (sbtsi) Add basic support
 for SB-TSI sensors
Message-ID: <20200331154630.GA41691@roeck-us.net>
References: <20200323233354.239365-1-kunyi@google.com>
 <20200323233354.239365-2-kunyi@google.com>
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On Mon, Mar 23, 2020 at 04:33:52PM -0700, Kun Yi wrote:
> SB Temperature Sensor Interface (SB-TSI) is an SMBus compatible
> interface that reports AMD SoC's Ttcl (normalized temperature),
> and resembles a typical 8-pin remote temperature sensor's I2C interface
> to BMC.
> 
> This commit adds basic support using this interface to read CPU
> temperature, and read/write high/low CPU temp thresholds.
> 
> To instantiate this driver on an AMD CPU with SB-TSI
> support, the i2c bus number would be the bus connected from the board
> management controller (BMC) to the CPU. The i2c address is specified in
> Section 6.3.1 of the spec [1]: The SB-TSI address is normally 98h for socket 0
> and 90h for socket 1, but it could vary based on hardware address select pins.
> 
> [1]: https://www.amd.com/system/files/TechDocs/56255_OSRR.pdf
> 
> Test status: tested reading temp1_input, and reading/writing
> temp1_max/min.
> 
> Signed-off-by: Kun Yi <kunyi@google.com>
> Change-Id: I85ec65a57e8d73d7343aa9e250860ec85bfa79e5
> ---
>  drivers/hwmon/Kconfig      |  10 ++
>  drivers/hwmon/Makefile     |   1 +
>  drivers/hwmon/sbtsi_temp.c | 261 +++++++++++++++++++++++++++++++++++++
>  3 files changed, 272 insertions(+)
>  create mode 100644 drivers/hwmon/sbtsi_temp.c
> 
> diff --git a/drivers/hwmon/Kconfig b/drivers/hwmon/Kconfig
> index 05a30832c6ba..9585dcd01d1b 100644
> --- a/drivers/hwmon/Kconfig
> +++ b/drivers/hwmon/Kconfig
> @@ -1412,6 +1412,16 @@ config SENSORS_RASPBERRYPI_HWMON
>  	  This driver can also be built as a module. If so, the module
>  	  will be called raspberrypi-hwmon.
>  
> +config SENSORS_SBTSI
> +	tristate "Emulated SB-TSI temperature sensor"
> +	depends on I2C
> +	help
> +	  If you say yes here you get support for emulated temperature
> +	  sensors on AMD SoCs with SB-TSI interface connected to a BMC device.
> +
> +	  This driver can also be built as a module. If so, the module will
> +	  be called sbtsi_temp.
> +
>  config SENSORS_SHT15
>  	tristate "Sensiron humidity and temperature sensors. SHT15 and compat."
>  	depends on GPIOLIB || COMPILE_TEST
> diff --git a/drivers/hwmon/Makefile b/drivers/hwmon/Makefile
> index b0b9c8e57176..cd109f003ce4 100644
> --- a/drivers/hwmon/Makefile
> +++ b/drivers/hwmon/Makefile
> @@ -152,6 +152,7 @@ obj-$(CONFIG_SENSORS_POWR1220)  += powr1220.o
>  obj-$(CONFIG_SENSORS_PWM_FAN)	+= pwm-fan.o
>  obj-$(CONFIG_SENSORS_RASPBERRYPI_HWMON)	+= raspberrypi-hwmon.o
>  obj-$(CONFIG_SENSORS_S3C)	+= s3c-hwmon.o
> +obj-$(CONFIG_SENSORS_SBTSI)	+= sbtsi_temp.o
>  obj-$(CONFIG_SENSORS_SCH56XX_COMMON)+= sch56xx-common.o
>  obj-$(CONFIG_SENSORS_SCH5627)	+= sch5627.o
>  obj-$(CONFIG_SENSORS_SCH5636)	+= sch5636.o
> diff --git a/drivers/hwmon/sbtsi_temp.c b/drivers/hwmon/sbtsi_temp.c
> new file mode 100644
> index 000000000000..cc452cb29c2c
> --- /dev/null
> +++ b/drivers/hwmon/sbtsi_temp.c
> @@ -0,0 +1,261 @@
> +// SPDX-License-Identifier: GPL-2.0-or-later
> +/*
> + * sbtsi_temp.c - hwmon driver for a SBI Temperature Sensor Interface (SB-TSI)
> + *                compliant AMD SoC temperature device.
> + *
> + * Copyright (c) 2020, Google Inc.
> + * Copyright (c) 2020, Kun Yi <kunyi@google.com>
> + */
> +
> +#include <linux/err.h>
> +#include <linux/i2c.h>
> +#include <linux/init.h>
> +#include <linux/hwmon.h>
> +#include <linux/module.h>
> +#include <linux/mutex.h>
> +#include <linux/of_device.h>
> +#include <linux/of.h>
> +
> +/*
> + * SB-TSI registers only support SMBus byte data access. "_INT" registers are
> + * the integer part of a temperature value or limit, and "_DEC" registers are
> + * corresponding decimal parts.
> + */
> +#define SBTSI_REG_TEMP_INT		0x01 /* RO */
> +#define SBTSI_REG_STATUS		0x02 /* RO */
> +#define SBTSI_REG_CONFIG		0x03 /* RO */
> +#define SBTSI_REG_TEMP_HIGH_INT		0x07 /* RW */
> +#define SBTSI_REG_TEMP_LOW_INT		0x08 /* RW */
> +#define SBTSI_REG_TEMP_DEC		0x10 /* RW */
> +#define SBTSI_REG_TEMP_HIGH_DEC		0x13 /* RW */
> +#define SBTSI_REG_TEMP_LOW_DEC		0x14 /* RW */
> +#define SBTSI_REG_REV			0xFF /* RO */
> +
> +#define SBTSI_CONFIG_READ_ORDER_SHIFT	5
> +
> +#define SBTSI_TEMP_MIN	0
> +#define SBTSI_TEMP_MAX	255875
> +#define SBTSI_REV_MAX_VALID_ID	4
> +
> +/* Each client has this additional data */
> +struct sbtsi_data {
> +	struct i2c_client *client;
> +	struct mutex lock;
> +};
> +
> +/*
> + * From SB-TSI spec: CPU temperature readings and limit registers encode the
> + * temperature in increments of 0.125 from 0 to 255.875. The "high byte"
> + * register encodes the base-2 of the integer portion, and the upper 3 bits of
> + * the "low byte" encode in base-2 the decimal portion.
> + *
> + * e.g. INT=0x19, DEC=0x20 represents 25.125 degrees Celsius
> + *
> + * Therefore temperature in millidegree Celsius =
> + *   (INT + DEC / 256) * 1000 = (INT * 8 + DEC / 32) * 125
> + */
> +static inline int sbtsi_reg_to_mc(s32 integer, s32 decimal)
> +{
> +	return ((integer << 3) + (decimal >> 5)) * 125;
> +}
> +
> +/*
> + * Inversely, given temperature in millidegree Celsius
> + *   INT = (TEMP / 125) / 8
> + *   DEC = ((TEMP / 125) % 8) * 32
> + * Caller have to make sure temp doesn't exceed 255875, the max valid value.
> + */
> +static inline void sbtsi_mc_to_reg(s32 temp, u8 *integer, u8 *decimal)
> +{
> +	temp /= 125;
> +	*integer = temp >> 3;
> +	*decimal = (temp & 0x7) << 5;
> +}
> +
> +static int sbtsi_read(struct device *dev, enum hwmon_sensor_types type,
> +		      u32 attr, int channel, long *val)
> +{
> +	struct sbtsi_data *data = dev_get_drvdata(dev);
> +	s32 temp_int, temp_dec;
> +	int err, reg_int, reg_dec;
> +	u8 read_order;
> +
> +	if (type != hwmon_temp)
> +		return -EINVAL;
> +
> +	read_order = 0;
> +	switch (attr) {
> +	case hwmon_temp_input:
> +		/*
> +		 * ReadOrder bit specifies the reading order of integer and
> +		 * decimal part of CPU temp for atomic reads. If bit == 0,
> +		 * reading integer part triggers latching of the decimal part,
> +		 * so integer part should be read first. If bit == 1, read
> +		 * order should be reversed.
> +		 */
> +		err = i2c_smbus_read_byte_data(data->client, SBTSI_REG_CONFIG);
> +		if (err < 0)
> +			return err;
> +
> +		read_order = (u8)err & BIT(SBTSI_CONFIG_READ_ORDER_SHIFT);
> +		reg_int = SBTSI_REG_TEMP_INT;
> +		reg_dec = SBTSI_REG_TEMP_DEC;
> +		break;
> +	case hwmon_temp_max:
> +		reg_int = SBTSI_REG_TEMP_HIGH_INT;
> +		reg_dec = SBTSI_REG_TEMP_HIGH_DEC;
> +		break;
> +	case hwmon_temp_min:
> +		reg_int = SBTSI_REG_TEMP_LOW_INT;
> +		reg_dec = SBTSI_REG_TEMP_LOW_DEC;
> +		break;
> +	default:
> +		return -EINVAL;
> +	}
> +
> +	if (read_order == 0) {
> +		temp_int = i2c_smbus_read_byte_data(data->client, reg_int);
> +		temp_dec = i2c_smbus_read_byte_data(data->client, reg_dec);
> +	} else {
> +		temp_dec = i2c_smbus_read_byte_data(data->client, reg_dec);
> +		temp_int = i2c_smbus_read_byte_data(data->client, reg_int);
> +	}
> +
> +	if (temp_int < 0)
> +		return temp_int;
> +	if (temp_dec < 0)
> +		return temp_dec;
> +
> +	*val = sbtsi_reg_to_mc(temp_int, temp_dec);
> +
> +	return 0;
> +}
> +
> +static int sbtsi_write(struct device *dev, enum hwmon_sensor_types type,
> +		       u32 attr, int channel, long val)
> +{
> +	struct sbtsi_data *data = dev_get_drvdata(dev);
> +	int reg_int, reg_dec, err;
> +	u8 temp_int, temp_dec;
> +
> +	if (type != hwmon_temp)
> +		return -EINVAL;
> +
> +	switch (attr) {
> +	case hwmon_temp_max:
> +		reg_int = SBTSI_REG_TEMP_HIGH_INT;
> +		reg_dec = SBTSI_REG_TEMP_HIGH_DEC;
> +		break;
> +	case hwmon_temp_min:
> +		reg_int = SBTSI_REG_TEMP_LOW_INT;
> +		reg_dec = SBTSI_REG_TEMP_LOW_DEC;
> +		break;
> +	default:
> +		return -EINVAL;
> +	}
> +
> +	val = clamp_val(val, SBTSI_TEMP_MIN, SBTSI_TEMP_MAX);
> +	mutex_lock(&data->lock);
> +	sbtsi_mc_to_reg(val, &temp_int, &temp_dec);
> +	err = i2c_smbus_write_byte_data(data->client, reg_int, temp_int);
> +	if (err)
> +		goto exit;
> +
> +	err = i2c_smbus_write_byte_data(data->client, reg_dec, temp_dec);
> +exit:
> +	mutex_unlock(&data->lock);
> +	return err;
> +}
> +
> +static umode_t sbtsi_is_visible(const void *data,
> +				enum hwmon_sensor_types type,
> +				u32 attr, int channel)
> +{
> +	switch (type) {
> +	case hwmon_temp:
> +		switch (attr) {
> +		case hwmon_temp_input:
> +			return 0444;
> +		case hwmon_temp_min:
> +			return 0644;
> +		case hwmon_temp_max:
> +			return 0644;
> +		}
> +		break;
> +	default:
> +		break;
> +	}
> +	return 0;
> +}
> +
> +static const struct hwmon_channel_info *sbtsi_info[] = {
> +	HWMON_CHANNEL_INFO(chip,
> +			   HWMON_C_REGISTER_TZ),
> +	HWMON_CHANNEL_INFO(temp,
> +			   HWMON_T_INPUT | HWMON_T_MIN | HWMON_T_MAX),
> +	NULL
> +};
> +
> +static const struct hwmon_ops sbtsi_hwmon_ops = {
> +	.is_visible = sbtsi_is_visible,
> +	.read = sbtsi_read,
> +	.write = sbtsi_write,
> +};
> +
> +static const struct hwmon_chip_info sbtsi_chip_info = {
> +	.ops = &sbtsi_hwmon_ops,
> +	.info = sbtsi_info,
> +};
> +
> +static int sbtsi_probe(struct i2c_client *client,
> +		       const struct i2c_device_id *id)
> +{
> +	struct device *dev = &client->dev;
> +	struct device *hwmon_dev;
> +	struct sbtsi_data *data;
> +
> +	data = devm_kzalloc(dev, sizeof(struct sbtsi_data), GFP_KERNEL);
> +	if (!data)
> +		return -ENOMEM;
> +
> +	data->client = client;
> +	mutex_init(&data->lock);
> +
> +	dev_set_drvdata(dev, data);
> +

This is not needed.

Guenter

> +	hwmon_dev =
> +		devm_hwmon_device_register_with_info(dev, client->name, data,
> +						     &sbtsi_chip_info, NULL);
> +
> +	return PTR_ERR_OR_ZERO(hwmon_dev);
> +}
> +
> +static const struct i2c_device_id sbtsi_id[] = {
> +	{"sbtsi", 0},
> +	{}
> +};
> +MODULE_DEVICE_TABLE(i2c, sbtsi_id);
> +
> +static const struct of_device_id __maybe_unused sbtsi_of_match[] = {
> +	{
> +		.compatible = "amd,sbtsi",
> +	},
> +	{ },
> +};
> +MODULE_DEVICE_TABLE(of, sbtsi_of_match);
> +
> +static struct i2c_driver sbtsi_driver = {
> +	.class = I2C_CLASS_HWMON,
> +	.driver = {
> +		.name = "sbtsi",
> +		.of_match_table = of_match_ptr(sbtsi_of_match),
> +	},
> +	.probe = sbtsi_probe,
> +	.id_table = sbtsi_id,
> +};
> +
> +module_i2c_driver(sbtsi_driver);
> +
> +MODULE_AUTHOR("Kun Yi <kunyi@google.com>");
> +MODULE_DESCRIPTION("Hwmon driver for AMD SB-TSI emulated sensor");
> +MODULE_LICENSE("GPL");