Message-ID: <476e9c68-4532-ec07-8244-5a8aa2fbc599@roeck-us.net>
Date:   Thu, 19 Mar 2020 16:30:58 -0700
From:   Guenter Roeck <linux@...ck-us.net>
To:     Kun Yi <kunyi@...gle.com>, jdelvare@...e.com, robh+dt@...nel.org,
        mark.rutland@....com
Cc:     openbmc@...ts.ozlabs.org, joel@....id.au,
        linux-hwmon@...r.kernel.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH linux hwmon-next v1 1/3] hwmon: (sbtsi) Add basic support
 for SB-TSI sensors

On 3/19/20 3:48 PM, 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.
> 
> Test status: tested reading temp1_input, and reading/writing
> temp1_max/min.
> 

How do I instantiate this driver on a system with an AMD CPU
(in other words, what is the i2c bus and the i2c address) ?

> Signed-off-by: Kun Yi <kunyi@...gle.com>
> ---
>  drivers/hwmon/Kconfig      |  10 ++
>  drivers/hwmon/Makefile     |   1 +
>  drivers/hwmon/sbtsi_temp.c | 218 +++++++++++++++++++++++++++++++++++++
>  3 files changed, 229 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..f998d944a515
> --- /dev/null
> +++ b/drivers/hwmon/sbtsi_temp.c
> @@ -0,0 +1,218 @@
> +// 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@...gle.com>
> + */
> +
> +#include <linux/device.h>
> +#include <linux/init.h>
> +#include <linux/i2c.h>
> +#include <linux/module.h>
> +#include <linux/mutex.h>
> +#include <linux/hwmon.h>
> +#include <linux/hwmon-sysfs.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)

Unnecessary ( ) around literals.

> +
> +struct sbtsi_data {
> +	struct device *dev;
> +	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_REGS_TO_TEMP(s32 integer, s32 decimal)
> +{
> +	return (((u32)integer << 3) + ((u32)decimal >> 5)) * 125;

Why pass s32 as parameter just to typecast to u32 ? The values
are known to be between 0 and 255, and thus will never be negative,
even with s32, so this is really unnecessary.

> +}
> +
> +/*
> + * 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_TEMP_TO_REGS(u32 temp, u8 *integer, u8 *decimal)
> +{
> +	temp /= 125;
> +	*integer = temp >> 3;
> +	*decimal = (temp & 0x7) << 5;
> +}
> +
> +static ssize_t sbtsi_show_temp(struct device *dev,
> +			       struct device_attribute *attr, char *buf)
> +{
> +	struct sbtsi_data *data = dev_get_drvdata(dev);
> +	struct i2c_client *client = data->client;
> +	s32 err, temp_int, temp_dec;
> +	u8 read_order;
> +
> +	/*
> +	 * 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(client, SBTSI_REG_CONFIG);
> +	if (err < 0)
> +		return err;
> +
> +	read_order = (u8)err & BIT(SBTSI_CONFIG_READ_ORDER_SHIFT);
> +
> +	if (read_order == 0) {
> +		temp_int = i2c_smbus_read_byte_data(client, SBTSI_REG_TEMP_INT);
> +		temp_dec = i2c_smbus_read_byte_data(client, SBTSI_REG_TEMP_DEC);
> +	} else {
> +		temp_dec = i2c_smbus_read_byte_data(client, SBTSI_REG_TEMP_DEC);
> +		temp_int = i2c_smbus_read_byte_data(client, SBTSI_REG_TEMP_INT);
> +	}
> +
> +	if (temp_int < 0)
> +		return temp_int;
> +	if (temp_dec < 0)
> +		return temp_dec;
> +
> +	return scnprintf(buf, PAGE_SIZE, "%d\n",
> +			 SBTSI_REGS_TO_TEMP(temp_int, temp_dec));
> +}
> +
> +#define sbtsi_show_temp_limit(name, REG) \
> +static ssize_t sbtsi_show_##name(struct device *dev, \
> +				 struct device_attribute *attr, char *buf) \
> +{ \
> +	struct sbtsi_data *data = dev_get_drvdata(dev); \
> +	struct i2c_client *client = data->client; \
> +	s32 temp_int, temp_dec; \
> +\
> +	temp_int = i2c_smbus_read_byte_data(client, REG##_INT); \
> +	temp_dec = i2c_smbus_read_byte_data(client, REG##_DEC); \
> +\
> +	if (temp_int < 0) \
> +		return temp_int; \
> +	if (temp_dec < 0) \
> +		return temp_dec; \
> +\
> +	return scnprintf(buf, PAGE_SIZE, "%d\n", \
> +			 SBTSI_REGS_TO_TEMP(temp_int, temp_dec)); \
> +}
> +
> +sbtsi_show_temp_limit(temp1_min, SBTSI_REG_TEMP_LOW);
> +sbtsi_show_temp_limit(temp1_max, SBTSI_REG_TEMP_HIGH);
> +
> +#define sbtsi_set_temp_limit(name, REG) \
> +static ssize_t sbtsi_set_##name(struct device *dev, \
> +				struct device_attribute *attr, \
> +				const char *buf, size_t count) \
> +{ \
> +	struct sbtsi_data *data = dev_get_drvdata(dev); \
> +	struct i2c_client *client = data->client; \
> +	long val; \
> +	u8 temp_int, temp_dec; \
> +	int err = kstrtol(buf, 10, &val); \
> +	if (err) \
> +		return err; \
> +\
> +	val = clamp_val(val, SBTSI_TEMP_MIN, SBTSI_TEMP_MAX); \
> +	mutex_lock(&data->lock); \
> +	SBTSI_TEMP_TO_REGS(val, &temp_int, &temp_dec); \
> +	i2c_smbus_write_byte_data(client, REG##_INT, temp_int); \
> +	i2c_smbus_write_byte_data(client, REG##_DEC, temp_dec); \
> +	mutex_unlock(&data->lock); \
> +\
> +	return count; \
> +}
> +
> +sbtsi_set_temp_limit(temp1_min, SBTSI_REG_TEMP_LOW);
> +sbtsi_set_temp_limit(temp1_max, SBTSI_REG_TEMP_HIGH);
> +
> +static SENSOR_DEVICE_ATTR(temp1_input, 0444, sbtsi_show_temp, NULL, 0);
> +static SENSOR_DEVICE_ATTR(temp1_min, 0644, sbtsi_show_temp1_min,
> +			  sbtsi_set_temp1_min, 1);
> +static SENSOR_DEVICE_ATTR(temp1_max, 0644, sbtsi_show_temp1_max,
> +			  sbtsi_set_temp1_max, 2);
> +
> +static struct attribute *sbtsi_attrs[] = {
> +	&sensor_dev_attr_temp1_input.dev_attr.attr,
> +	&sensor_dev_attr_temp1_min.dev_attr.attr,
> +	&sensor_dev_attr_temp1_max.dev_attr.attr,
> +	NULL,
> +};
> +ATTRIBUTE_GROUPS(sbtsi);
> +
> +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_groups(dev, client->name, data,
> +						       sbtsi_groups);

Please rewrite to use the devm_hwmon_device_register_with_info() API.

> +	if (IS_ERR(hwmon_dev))
> +		return PTR_ERR(hwmon_dev);
> +
> +	dev_info(dev, "sensor '%s'\n", client->name);

Is that really valuable / necessary ?

> +
> +	return 0;
> +}
> +
> +static const struct i2c_device_id sbtsi_id[] = {
> +	{"sbtsi", 0},
> +	{}
> +};
> +MODULE_DEVICE_TABLE(i2c, sbtsi_id);
> +
> +static struct i2c_driver sbtsi_driver = {
> +	.class = I2C_CLASS_HWMON,
> +	.driver = {
> +		.name = "sbtsi",
> +	},
> +	.probe = sbtsi_probe,
> +	.id_table = sbtsi_id,
> +};
> +
> +module_i2c_driver(sbtsi_driver);
> +
> +MODULE_AUTHOR("Kun Yi <kunyi@...gle.com>");
> +MODULE_DESCRIPTION("Hwmon driver for AMD SB-TSI emulated sensor");
> +MODULE_LICENSE("GPL");
> 

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