Message-ID: <DM6PR12MB4388BC99671A1B82F811A549E8F20@DM6PR12MB4388.namprd12.prod.outlook.com>
Date:   Thu, 3 Dec 2020 18:06:33 +0000
From:   "Chatradhi, Naveen Krishna" <NaveenKrishna.Chatradhi@....com>
To:     Guenter Roeck <linux@...ck-us.net>, Kun Yi <kunyi@...gle.com>
CC:     "jdelvare@...e.com" <jdelvare@...e.com>,
        "robh+dt@...nel.org" <robh+dt@...nel.org>,
        "mark.rutland@....com" <mark.rutland@....com>,
        "Venkatesh, Supreeth" <Supreeth.Venkatesh@....com>,
        "openbmc@...ts.ozlabs.org" <openbmc@...ts.ozlabs.org>,
        "linux-hwmon@...r.kernel.org" <linux-hwmon@...r.kernel.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH linux hwmon-next v4 1/3] hwmon: (sbtsi) Add basic support
 for SB-TSI sensors

[AMD Official Use Only - Approved for External Use]

Hi Kun Yi,

> Test status: tested reading temp1_input, and reading/writing 
> temp1_max/min.

Tested the above at our end from an arm based BMC connected to the 2P Rome machine, it works fine. 

Regards,
Naveenk

-----Original Message-----
From: Guenter Roeck <linux@...ck-us.net> 
Sent: Thursday, December 3, 2020 7:08 AM
To: Kun Yi <kunyi@...gle.com>
Cc: jdelvare@...e.com; robh+dt@...nel.org; mark.rutland@....com; Venkatesh, Supreeth <Supreeth.Venkatesh@....com>; openbmc@...ts.ozlabs.org; linux-hwmon@...r.kernel.org; devicetree@...r.kernel.org; linux-kernel@...r.kernel.org
Subject: Re: [PATCH linux hwmon-next v4 1/3] hwmon: (sbtsi) Add basic support for SB-TSI sensors

[CAUTION: External Email]

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://nam11.safelinks.protection.outlook.com/?url=https%3A%2F%2Fwww.
> amd.com%2Fsystem%2Ffiles%2FTechDocs%2F56255_OSRR.pdf&amp;data=04%7C01%
> 7CNaveenKrishna.Chatradhi%40amd.com%7C1a8cb0ebe4bb43bc759808d8972c562f
> %7C3dd8961fe4884e608e11a82d994e183d%7C0%7C1%7C637425563976853035%7CUnk
> nown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWw
> iLCJXVCI6Mn0%3D%7C1000&amp;sdata=oH5YmE000EUVGVxruzI%2FBRnWOKptlG%2Bpf
> yKferIwYME%3D&amp;reserved=0
>
> Test status: tested reading temp1_input, and reading/writing 
> temp1_max/min.
>
> Signed-off-by: Kun Yi <kunyi@...gle.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@...gle.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@...gle.com>"); MODULE_DESCRIPTION("Hwmon 
> +driver for AMD SB-TSI emulated sensor"); MODULE_LICENSE("GPL");
> --
> 2.29.2.454.gaff20da3a2-goog
>

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