Re: [PATCH linux hwmon-next v4 1/3] hwmon: (sbtsi) Add basic support for SB-TSI sensors

Guenter Roeck
2020-12-03T01:38:49Z

On Wed, Dec 02, 2020 at 08:55:59AM -0800, 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>
> ---
> drivers/hwmon/Kconfig | 10 ++
> drivers/hwmon/Makefile | 1 +
> drivers/hwmon/sbtsi_temp.c | 265 +++++++++++++++++++++++++++++++++++++
> 3 files changed, 276 insertions(+)
> create mode 100644 drivers/hwmon/sbtsi_temp.c
>
> diff --git a/drivers/hwmon/Kconfig b/drivers/hwmon/Kconfig
> index 3c059fc23cd6..3d6a809700ae 100644
> --- a/drivers/hwmon/Kconfig
> +++ b/drivers/hwmon/Kconfig
> @@ -1522,6 +1522,16 @@ config SENSORS_SL28CPLD
> This driver can also be built as a module. If so, the module
> will be called sl28cpld-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 01ca5d3fbad4..ee8c037919da 100644
> --- a/drivers/hwmon/Makefile
> +++ b/drivers/hwmon/Makefile
> @@ -160,6 +160,7 @@ 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..6b0a7b9df1f3
> --- /dev/null
> +++ b/drivers/hwmon/sbtsi_temp.c
> @@ -0,0 +1,265 @@
> +// 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_CONFIG_READ_ORDER_SHIFT 5
> +
> +#define SBTSI_TEMP_MIN 0
> +#define SBTSI_TEMP_MAX 255875
> +
> +/* 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;
> + bool reading_input;
> +
> + if (type != hwmon_temp)
> + return -EINVAL;

Unnecessary check.

> +
> + reading_input = false;
> + switch (attr) {
> + case hwmon_temp_input:
> + reading_input = true;
> + /*
> + * 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;
> +
> + mutex_lock(&data->lock);
> + if (err & BIT(SBTSI_CONFIG_READ_ORDER_SHIFT)) {
> + temp_dec = i2c_smbus_read_byte_data(data->client,
> + SBTSI_REG_TEMP_DEC);
> + temp_int = i2c_smbus_read_byte_data(data->client,
> + SBTSI_REG_TEMP_INT);
> + } else {
> + temp_int = i2c_smbus_read_byte_data(data->client,
> + SBTSI_REG_TEMP_INT);
> + temp_dec = i2c_smbus_read_byte_data(data->client,
> + SBTSI_REG_TEMP_DEC);
> + }
> + mutex_unlock(&data->lock);
> + 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 (!reading_input) {
> + temp_int = i2c_smbus_read_byte_data(data->client, reg_int);
> + temp_dec = i2c_smbus_read_byte_data(data->client, reg_dec);
> + }

This adds unnecessary complexity. I would suggest to move the calls
to the case statements and drop reading_input as well as reg_int,
reg_dec.

Also, I just realized that the mutex is needed here as well, since
the values might be written while being read, which could result in
inconsistent read values. Example: Limit is changed from 100 to 99.75.
Since the integer value is written first, it is possible that 99.0
is returned.

> +
> + 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;

This check is really unnecessary.

> +
> + 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);
> +
> + hwmon_dev =
> + devm_hwmon_device_register_with_info(dev, client->name, data,

Line length limit is now 100 columns, so the above line split is unnecessary.

> + &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");
> --
> 2.29.2.454.gaff20da3a2-goog
>