RE: [PATCH 1/3] hwmon: sbrmi: Add support for sbrmi power module

["Chatradhi, Naveen Krishna" <NaveenKrishna.Chatradhi@amd.com>]

[AMD Official Use Only]

Hi Guenter,

-----Original Message-----
From: Guenter Roeck <groeck7@gmail.com> On Behalf Of Guenter Roeck
Sent: Monday, June 28, 2021 8:29 PM
To: Chatradhi, Naveen Krishna <NaveenKrishna.Chatradhi@amd.com>; linux-hwmon@vger.kernel.org
Cc: Gupta, Akshay <Akshay.Gupta@amd.com>
Subject: Re: [PATCH 1/3] hwmon: sbrmi: Add support for sbrmi power module

[CAUTION: External Email]

On 6/25/21 6:25 AM, Naveen Krishna Chatradhi wrote:
> From: Akshay Gupta <Akshay.Gupta@amd.com>
>
> On AMD platforms the Out-of-band access is provided by Advanced 
> Platform Management

This is a bit too long for checkpatch.

> Link (APML), APML is a SMBus v2.0 compatible 2-wire processor client interface.
> APML is also referred as the sideband interface (SBI).
>
> APML is used to communicate with the Remote Management Interface 
> (SB-Remote Management Interface (SB-RMI) which provides Soft Mailbox 
> messages to report power consumption and power limits of the CPU socket.
>
> - This module add support to read power consumption,
>    power limit & max power limit and write power limit.
> - To instantiate this driver on an AMD CPU with SB-RMI support,
>    the i2c bus number would be the bus connected from the board
>    management controller (BMC) to the CPU.
>

This is a bit vague. Would this driver be instantiated on the host CPU or on the BMC ?

> Signed-off-by: Akshay Gupta <Akshay.Gupta@amd.com>
> Signed-off-by: Naveen Krishna Chatradhi <nchatrad@amd.com>
> ---
>   drivers/hwmon/Kconfig  |  10 ++
>   drivers/hwmon/Makefile |   1 +
>   drivers/hwmon/sbrmi.c  | 394 +++++++++++++++++++++++++++++++++++++++++
>   3 files changed, 405 insertions(+)
>   create mode 100644 drivers/hwmon/sbrmi.c
>
> diff --git a/drivers/hwmon/Kconfig b/drivers/hwmon/Kconfig index 
> 87624902ea80..d1813ea8382c 100644
> --- a/drivers/hwmon/Kconfig
> +++ b/drivers/hwmon/Kconfig
> @@ -1551,6 +1551,16 @@ config SENSORS_SBTSI
>         This driver can also be built as a module. If so, the module will
>         be called sbtsi_temp.
>
> +config SENSORS_SBRMI
> +     tristate "Emulated SB-RMI sensor"
> +     depends on I2C
> +     help
> +       If you say yes here you get support for emulated RMI
> +       sensors on AMD SoCs with APML interface connected to a BMC device.
> +
> +       This driver can also be built as a module. If so, the module will
> +       be called sbrmi.
> +
>   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 
> 59e78bc212cf..8031acf58936 100644
> --- a/drivers/hwmon/Makefile
> +++ b/drivers/hwmon/Makefile
> @@ -164,6 +164,7 @@ 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-$(CONFIG_SENSORS_SBRMI)  += sbrmi.o
>   obj-$(CONFIG_SENSORS_SCH56XX_COMMON)+= sch56xx-common.o
>   obj-$(CONFIG_SENSORS_SCH5627)       += sch5627.o
>   obj-$(CONFIG_SENSORS_SCH5636)       += sch5636.o
> diff --git a/drivers/hwmon/sbrmi.c b/drivers/hwmon/sbrmi.c new file 
> mode 100644 index 000000000000..c35829513459
> --- /dev/null
> +++ b/drivers/hwmon/sbrmi.c
> @@ -0,0 +1,394 @@
> +// SPDX-License-Identifier: GPL-2.0-or-later
> +/*
> + * sbrmi.c - hwmon driver for a SB-RMI mailbox
> + *           compliant AMD SoC device.
> + *
> + * Copyright (C) 2020-2021 Advanced Micro Devices, Inc.
> + */
> +
> +#include <linux/err.h>
> +#include <linux/hwmon.h>
> +#include <linux/i2c.h>
> +#include <linux/init.h>
> +#include <linux/module.h>
> +#include <linux/mutex.h>
> +#include <linux/of.h>
> +#include <linux/of_device.h>

I don't immediately see why this include is needed.

> +#include <asm-generic/ioctl.h>

This looks wrong, and I don't immediately see why it would be needed.

> +#include <linux/delay.h>

Alphabetic include file order, please.

> +
> +/* Do not allow setting negative power limit */ #define SBRMI_PWR_MIN 
> +0
> +/* Mask for Status Register bit[1] */ #define SW_ALERT_MASK 0x2
> +

Please always use

#define<space>DEFINITION<tab>value
                         ^^^^^

> +/* Software Interrupt for triggering */
> +#define START_CMD    0x80
> +#define TRIGGER_MAILBOX      0x01
> +
> +/*
> + * SB-RMI supports soft mailbox service request to MP1 (power 
> +management
> + * firmware) through SBRMI inbound/outbound message registers.
> + * SB-RMI message IDs
> + */
> +enum sbrmi_msg_id {
> +     SBRMI_READ_PKG_PWR_CONSUMPTION = 0x1,
> +     SBRMI_WRITE_PKG_PWR_LIMIT,
> +     SBRMI_READ_PKG_PWR_LIMIT,
> +     SBRMI_READ_PKG_MAX_PWR_LIMIT,
> +};
> +
> +/* SB-RMI registers */
> +enum sbrmi_reg {
> +     SBRMI_CTRL              = 0x01,
> +     SBRMI_STATUS,
> +     SBRMI_OUTBNDMSG0        = 0x30,
> +     SBRMI_OUTBNDMSG1,
> +     SBRMI_OUTBNDMSG2,
> +     SBRMI_OUTBNDMSG3,
> +     SBRMI_OUTBNDMSG4,
> +     SBRMI_OUTBNDMSG5,
> +     SBRMI_OUTBNDMSG6,
> +     SBRMI_OUTBNDMSG7,
> +     SBRMI_INBNDMSG0,
> +     SBRMI_INBNDMSG1,
> +     SBRMI_INBNDMSG2,
> +     SBRMI_INBNDMSG3,
> +     SBRMI_INBNDMSG4,
> +     SBRMI_INBNDMSG5,
> +     SBRMI_INBNDMSG6,
> +     SBRMI_INBNDMSG7,
> +     SBRMI_SW_INTERRUPT,
> +};
> +
> +/*
> + * Each client has this additional data  */

Please be consistent with comments: This does not really need to be a multi-line comment. While that does not really matter, you use a single-line comment to describe the next structure. Please make it both either single-line or multi-line.

> +struct sbrmi_data {
> +     struct i2c_client *client;
> +     struct mutex lock;
> +};
> +
> +/* Mailbox message data format */
> +union mailbox_word {
> +     u8 bytes[4];
> +     u32 value;

That strongly suggests that the driver will only work on either little-endian or big-endian systems, depending on the byte order of transfers. Please restrict it accordingly.

> +};
> +
> +struct sbrmi_mailbox_msg {
> +     u8 cmd;
> +     bool read;
> +     union mailbox_word data_in;
> +     union mailbox_word data_out;
> +};
> +
> +static int print_mailbox_error(struct sbrmi_data *data) {

Nit> Many functions only use data>client and, in some cases, dereference 
Nit> it
several times. It might be easier to just pass 'client'.

> +     int status;
> +
> +     /* Mailbox error code will be written by Firmware in
> +      * SBRMI::OutBndMsg_inst7 (SBRMI_x37)
> +      */

/*
  * Please use standard multi-line comments. Applies to entire driver.
  */

> +     status = i2c_smbus_read_byte_data(data->client, SBRMI_OUTBNDMSG7);
> +     if (status < 0) {
> +             pr_err("SMBUS translation failed\n");
> +             return status;
> +     }
> +
> +     switch (status) {
> +     case 0x0:       /* Success */
> +             break;
> +     case 0x1:
> +             pr_err("Mailbox message command is aborted\n");
> +             break;
> +     case 0x2:
> +             pr_err("Unknown mailbox message\n");
> +             break;
> +     case 0x3:
> +             pr_err("Invalid core is specified in mailbox message parameters\n");
> +             break;
> +     default:
> +             pr_err("Unknown Error\n");
> +     }

Is this noise necessary ? I am concerned that, if it occurs, it would be persistent and fill up the kernel log with noise.

> +
> +     return status;

Error codes are supposed to be negative and standard Linux error codes.
Please convert the above errors to standard Linux error codes.

> +}
> +
> +static int sbrmi_enable_alert(struct sbrmi_data *data) {
> +     int ctrl;
> +
> +     /* Enable the SB-RMI Software alert status
> +      * by writing 0 to bit 4 of Control register(0x1)
> +      */
> +     ctrl = i2c_smbus_read_byte_data(data->client, SBRMI_CTRL);
> +     if (ctrl < 0)
> +             return ctrl;
> +
> +     if (ctrl & 0x10) {
> +             ctrl &= ~0x10;
> +             return i2c_smbus_write_byte_data(data->client,
> +                                              SBRMI_CTRL, ctrl);
> +     }
> +
> +     return 0;
> +}
> +
> +static int rmi_mailbox_xfer(struct sbrmi_data *data,
> +                         struct sbrmi_mailbox_msg *msg) {
> +     union mailbox_word output, input;
> +     int i, err = 0, retry = 10;

Initializing 'err' is unnecessary.

> +     int sw_status;
> +
> +     mutex_lock(&data->lock);
> +
> +     err = sbrmi_enable_alert(data);
> +     if (err < 0)
> +             goto exit_unlock;
> +
> +     /* Indicate firmware a command is to be serviced */
> +     err = i2c_smbus_write_byte_data(data->client,
> +                                     SBRMI_INBNDMSG7, START_CMD);
> +     if (err < 0)
> +             goto exit_unlock;
> +
> +     /* Write the command to SBRMI::InBndMsg_inst0 */
> +     err = i2c_smbus_write_byte_data(data->client,
> +                                     SBRMI_INBNDMSG0, msg->cmd);
> +     if (err < 0)
> +             goto exit_mod;
> +
> +     /*
> +      * For both read and write the initiator (BMC) writes
> +      * Command Data In[31:0] to SBRMI::InBndMsg_inst[4:1]
> +      * SBRMI_x3C(MSB):SBRMI_x39(LSB)
> +      */
> +     input = msg->data_in;
> +     for (i = 0; i < 3; i++) {

This writes 3 bytes. Is that on purpose ? If so please explain since the above suggests that 4 bytes should be written.

> +             err = i2c_smbus_write_byte_data(data->client,
> +                                             (SBRMI_INBNDMSG1 + i),

Unnecessary ( )

> +                                             input.bytes[i]);
> +             if (err < 0)
> +                     goto exit_mod;
> +     }
> +
> +     /*
> +      * Write 0x01 to SBRMI::SoftwareInterrupt to notify firmware to
> +      * perform the requested read or write command
> +      */
> +     err = i2c_smbus_write_byte_data(data->client,
> +                                     SBRMI_SW_INTERRUPT, TRIGGER_MAILBOX);
> +     if (err < 0)
> +             goto exit_mod;
> +
> +     /*
> +      * Firmware will write SBRMI::Status[SwAlertSts]=1 to generate
> +      * an ALERT (if enabled) to initiator (BMC) to indicate completion
> +      * of the requested command
> +      */
> +     do {
> +             sw_status = i2c_smbus_read_byte_data(data->client,
> +                                                  SBRMI_STATUS);
> +             if (sw_status < 0) {
> +                     err = sw_status;
> +                     goto exit_mod;
> +             }
> +             if (sw_status & SW_ALERT_MASK)
> +                     break;
> +             usleep_range(50, 100);
> +     } while (retry--);
> +
> +     if (retry < 0) {
> +             pr_err("Firmware fail to indicate command 
> + colmpletion\n");

completion

> +             err = -1;
> +             goto exit_mod;
> +     }
> +
> +     /*
> +      * For a read operation, the initiator (BMC) reads the firmware response
> +      * Command Data Out[31:0] from SBRMI::OutBndMsg_inst[4:1]
> +      * {SBRMI_x34(MSB):SBRMI_x31(LSB)}.
> +      */
> +     if (msg->read) {
> +             for (i = 0; i < 4; i++) {
> +                     output.bytes[i] = i2c_smbus_read_byte_data(data->client,
> +                                                                
> + (SBRMI_OUTBNDMSG1 + i));

Unnecessary ().

> +                     if (output.bytes[i] < 0) {

output.bytes is defined as u8. This will not catch errors.

> +                             err = output.bytes[i];
> +                             goto exit_mod;
> +                     }
> +             }
> +     }
> +     msg->data_out = output;
> +
> +     /*
> +      * BMC must write 1'b1 to SBRMI::Status[SwAlertSts] to clear the
> +      * ALERT to initiator
> +      */
> +     err = i2c_smbus_write_byte_data(data->client, SBRMI_STATUS,
> +                                     (sw_status | SW_ALERT_MASK));

Unnecessary ().

> +
> +exit_mod:
> +     if (err < 0)
> +             pr_err("SMBUS translation failed\n");
> +     else
> +             err = print_mailbox_error(data);
> +exit_unlock:
> +     mutex_unlock(&data->lock);
> +     return err;
> +}
> +
> +static int sbrmi_read(struct device *dev, enum hwmon_sensor_types type,
> +                   u32 attr, int channel, long *val) {
> +     struct sbrmi_data *data = dev_get_drvdata(dev);
> +     struct sbrmi_mailbox_msg msg = { 0 };
> +     int ret;
> +
> +     if (type != hwmon_power)
> +             return -EINVAL;
> +
> +     msg.read = true;
> +     switch (attr) {
> +     case hwmon_power_input:
> +             msg.cmd = SBRMI_READ_PKG_PWR_CONSUMPTION;
> +             ret = rmi_mailbox_xfer(data, &msg);
> +             break;
> +     case hwmon_power_cap:
> +             msg.cmd = SBRMI_READ_PKG_PWR_LIMIT;
> +             ret = rmi_mailbox_xfer(data, &msg);
> +             break;
> +     case hwmon_power_cap_max:
> +             msg.cmd = SBRMI_READ_PKG_MAX_PWR_LIMIT;
> +             ret = rmi_mailbox_xfer(data, &msg);
> +             break;
> +     default:
> +             return -EINVAL;
> +     }
> +     /*
> +      * hwmon power attributes are in microWatt
> +      */
> +     *val = (long)msg.data_out.value * 1000;
> +     return ret;
> +}
> +
> +static int sbrmi_write(struct device *dev, enum hwmon_sensor_types type,
> +                    u32 attr, int channel, long val) {
> +     struct sbrmi_data *data = dev_get_drvdata(dev);
> +     struct sbrmi_mailbox_msg msg = { 0 };
> +
> +     if (type != hwmon_power && attr != hwmon_power_cap)
> +             return -EINVAL;
> +     /*
> +      * hwmon power attributes are in microWatt
> +      * mailbox read/write is in mWatt
> +      */
> +     val /= 1000;
> +
> +     msg.cmd = SBRMI_READ_PKG_MAX_PWR_LIMIT;
> +     msg.data_in.value = 0;
> +     msg.read = true;
> +     rmi_mailbox_xfer(data, &msg);
> +
> +     val = clamp_val(val, SBRMI_PWR_MIN, msg.data_out.value);
> +
> +     msg.cmd = SBRMI_WRITE_PKG_PWR_LIMIT;
> +     msg.data_in.value = val;
> +     msg.read = false;
> +
> +     return rmi_mailbox_xfer(data, &msg); }
> +
> +static umode_t sbrmi_is_visible(const void *data,
> +                             enum hwmon_sensor_types type,
> +                             u32 attr, int channel) {
> +     switch (type) {
> +     case hwmon_power:
> +             switch (attr) {
> +             case hwmon_power_input:
> +             case hwmon_power_cap_max:
> +                     return 0444;
> +             case hwmon_power_cap:
> +                     return 0644;
> +             }
> +             break;
> +     default:
> +             break;
> +     }
> +     return 0;
> +}
> +
> +static const struct hwmon_channel_info *sbrmi_info[] = {
> +     HWMON_CHANNEL_INFO(power,
> +                        HWMON_P_INPUT | HWMON_P_CAP | HWMON_P_CAP_MAX),
> +     NULL
> +};
> +
> +static const struct hwmon_ops sbrmi_hwmon_ops = {
> +     .is_visible = sbrmi_is_visible,
> +     .read = sbrmi_read,
> +     .write = sbrmi_write,
> +};
> +
> +static const struct hwmon_chip_info sbrmi_chip_info = {
> +     .ops = &sbrmi_hwmon_ops,
> +     .info = sbrmi_info,
> +};
> +
> +static int sbrmi_probe(struct i2c_client *client,
> +                    const struct i2c_device_id *id) {
> +     struct device *dev = &client->dev;
> +     struct device *hwmon_dev;
> +     struct sbrmi_data *data;
> +
> +     if (!i2c_check_functionality(client->adapter, I2C_FUNC_I2C)) {
> +             dev_err(&client->dev, "adapter does not support true 
> + I2C\n");

Why would that matter? It only uses SMBus functions.

> +             return -ENODEV;
> +     }
> +
> +     data = devm_kzalloc(dev, sizeof(struct sbrmi_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,
> +                                                      
> + &sbrmi_chip_info, NULL);
> +
> +     return PTR_ERR_OR_ZERO(hwmon_dev); }
> +
> +static const struct i2c_device_id sbrmi_id[] = {
> +     {"sbrmi", 0},
> +     {}
> +};
> +MODULE_DEVICE_TABLE(i2c, sbrmi_id);
> +
> +static const struct of_device_id __maybe_unused sbrmi_of_match[] = {
> +     {
> +             .compatible = "amd,sbrmi",
> +     },
> +     { },
> +};
> +MODULE_DEVICE_TABLE(of, sbrmi_of_match);
> +
> +static struct i2c_driver sbrmi_driver = {
> +     .class = I2C_CLASS_HWMON,
> +     .driver = {
> +             .name = "sbrmi",
> +             .of_match_table = of_match_ptr(sbrmi_of_match),
> +     },
> +     .probe = sbrmi_probe,
> +     .id_table = sbrmi_id,
> +};
> +
> +module_i2c_driver(sbrmi_driver);
> +
> +MODULE_AUTHOR("Akshay Gupta <akshay.gupta@amd.com>"); 
> +MODULE_DESCRIPTION("Hwmon driver for AMD SB-RMI emulated sensor"); 
> +MODULE_LICENSE("GPL");
[naveenk:] Thank you for your comments, we will address your comments and submit v2 soon.
>
[naveenk:] 
Regards,
Naveenk