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References: <20201202165601.1532213-1-kunyi@google.com> <20201202165601.1532213-2-kunyi@google.com>
 <20201203013748.GA228752@roeck-us.net>
In-Reply-To: <20201203013748.GA228752@roeck-us.net>
From:   Kun Yi <kunyi@google.com>
Date:   Fri, 11 Dec 2020 13:57:04 -0800
Message-ID: <CAGMNF6VwzAR8qe3oYGfn7pb9sKMe5dtWBBrRowNRK63pH-mkeA@mail.gmail.com>
Subject: Re: [PATCH linux hwmon-next v4 1/3] hwmon: (sbtsi) Add basic support
 for SB-TSI sensors
To:     Guenter Roeck <linux@roeck-us.net>
Cc:     jdelvare@suse.com, robh+dt@kernel.org, mark.rutland@arm.com,
        "Venkatesh, Supreeth" <supreeth.venkatesh@amd.com>,
        OpenBMC Maillist <openbmc@lists.ozlabs.org>,
        linux-hwmon@vger.kernel.org, devicetree@vger.kernel.org,
        linux-kernel@vger.kernel.org
Content-Type: text/plain; charset="UTF-8"
Precedence: bulk

Thanks Guenter for reviewing!

On Wed, Dec 2, 2020 at 5:37 PM Guenter Roeck <linux@roeck-us.net> wrote:
>
> 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.

Removed.

>
> > +
> > +     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.

Done.

>
> 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.

That's a good catch. Modified.

>
> > +
> > +     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.
Removed.
>
> > +
> > +     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.
Wow I didn't know.. Thanks! Adjusted a couple other lines based on the 100 cols.
>
> > +                                                  &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
> >


-- 
Regards,
Kun