PMBus协议规范介绍
PMBus是一套对电源进行配置、控制和监控的通讯协议标准。其最新版本为1.3，该规范还在不断演进中，比如新标准中新增的zone PMBus、AVSBus等特性。在其官网上有详细的规范文档，本节不尝试翻译规范文档，重点记录作者在了解PMBus过程中的疑问和解答。
PMBus与I2C、SMBus的区别？
PMBus在SMBus（System Management Bus）基础上增加了一套电源配置、控制和监控规范。SMBus最初是为电池智能管理而开发的一套标准，其基于I2C协议，并针对I2C协议的弱健壮性做了如下改进：
- 支持SMBALERT#中断；
- 支持错包检测（PEC）；
- 支持包超时；
- 支持START/STOP保护；
- 支持Host Notify Protocol协议；
PMBus监控哪些参数？告警分为几级？不同告警级别有什么样的应对措施？
PMBus支持电压、电流、功率、温度和风扇等参数的上下限监控，支持warning和fault 2级告警级别（如上图所示）。
- warning告警：表示监控参数异常，系统需引起关注，但可以继续运行，系统无需任何响应措施；
- fault告警：比warning告警级别高，系统会根据异常对设备的危害情况，进行设备控制电路重启(restart)或输出切断(shutdown)等处理；
告警产生时如何上报给主机？
告警上报一般有如下几种方式：
- 主机轮询PMBus设备；
- PMBus设备通过SMBALERT#中断通知主机；
- Host Notify Protocol(PMBus设备临时切换成总线主机(bus master),并发送一组特定协议通知系统主机)。
什么情况下告警会取消或清除？重启是否会清除告警？
任何warning或fault告警一旦上报，只有通过如下几种方式可以取消清除：
- PMBus设备接收到CLEAR_FAULTS命令；
- PMBus设备RESET引脚生效；
- PMBus设备通过CONTROL引脚或OPERATION命令关闭并重新打开；
- 断电；
- 如果异常一直存在，那么即使进行告警清除操作，告警会马上重新上报。
linux PMBus驱动设计分析
PMBus设备驱动位于linux/drivers/hwmon/pmbus，文件组织划分为3个部分：
比较有意思的是PMBus的通用设备驱动框架设计部分，其设计方案主要要解决如下2个问题：
- 支持PMBus设备厂商的自定义功能集。PMBus规范定义一套功能集，其中有些是基本功能，有些是可选功能；
- 支持PMBus设备厂商的自定义寄存器。
pmbus驱动框架的数据模型如下，其核心对象为i2c_client，即i2c设备对象，i2c_client继承于linux设备驱动模型device对象。pmbus设备信息通过设备驱动模型抽象接口driver_data访问，由pmbus_data对象实现。pmbus_data对象又关联如下2个主要对象：
- pmbus_driver_info：PMBus设备支持的功能集描述及相关接口，由pmbus设备实现。
- pmbus_sensor：PMBus设备支持的监控传感器对象链表，由voltage/current/power/temp/fan实现。
pmbus设备功能集识别有2种实现方式：
- 由pmbus_driver_info对象的identify接口完成，其工作原理是通过读取功能寄存器，如果读取成功，则说明设备支持此功能，否则不支持；
- 直接静态初始化pmbus_driver_info。
设备自定义寄存器通过虚拟寄存器（Virtual registers）统一到pmbus驱动框架中。pmbus通用设备驱动只看到标准寄存器和虚拟寄存器。虚拟寄存器到设备自定义寄存器的映射过程通过设备注册的4个接口：read_byte_data/read_word_data/write_word_data/write_byte来完成。
应用示例
1. 编写pmbus设备的smbus总线设备驱动并注册。如下i2c-10[1-3]为epld实现的4个i2c总线设备
/ # ls /sys/bus/i2c/devices/ -l
total 0
lrwxrwxrwx 1 root root 0 Jan 1 00:00 i2c-100 -> ../../../devices/i2c-100
lrwxrwxrwx 1 root root 0 Jan 1 00:00 i2c-101 -> ../../../devices/i2c-101
lrwxrwxrwx 1 root root 0 Jan 1 00:00 i2c-102 -> ../../../devices/i2c-102
lrwxrwxrwx 1 root root 0 Jan 1 00:00 i2c-103 -> ../../../devices/i2c-103 / # cats '/sys/bus/i2c/devices/i2c-10*/name'
/sys/bus/i2c/devices/i2c-100/name: WORK_EPLD1
/sys/bus/i2c/devices/i2c-101/name: WORK_EPLD2.0
/sys/bus/i2c/devices/i2c-102/name: WORK_EPLD2.1
/sys/bus/i2c/devices/i2c-103/name: WORK_NSE
/ #
2. 编写pmbus设备驱动并注册。如下为注册方法，hwmon[0-9]为注册的pmbus设备
echo tps53667 0x60 > /sys/bus/i2c/devices/i2c-100/new_device
echo tps53667 0x62 > /sys/bus/i2c/devices/i2c-100/new_device
echo tps53667 0x1060 > /sys/bus/i2c/devices/i2c-100/new_device
echo tps53667 0x1062 > /sys/bus/i2c/devices/i2c-100/new_device echo tps53667 0x60 > /sys/bus/i2c/devices/i2c-101/new_device
echo tps53667 0x60 > /sys/bus/i2c/devices/i2c-102/new_device echo tps53667 0x70 > /sys/bus/i2c/devices/i2c-103/new_device
echo tps53667 0x1071 > /sys/bus/i2c/devices/i2c-103/new_device
echo tps53667 0x2072 > /sys/bus/i2c/devices/i2c-103/new_device
echo tps53667 0x3073 > /sys/bus/i2c/devices/i2c-103/new_device / # ls /sys/class/hwmon/ -l
total 0
lrwxrwxrwx 1 root root 0 Jan 1 00:00 hwmon0 -> ../../devices/i2c-100/100-0060/hwmon/hwmon0
lrwxrwxrwx 1 root root 0 Jan 1 00:00 hwmon1 -> ../../devices/i2c-100/100-0062/hwmon/hwmon1
lrwxrwxrwx 1 root root 0 Jan 1 00:00 hwmon2 -> ../../devices/i2c-100/100-1060/hwmon/hwmon2
lrwxrwxrwx 1 root root 0 Jan 1 00:00 hwmon3 -> ../../devices/i2c-100/100-1062/hwmon/hwmon3
lrwxrwxrwx 1 root root 0 Jan 1 00:00 hwmon4 -> ../../devices/i2c-101/101-0060/hwmon/hwmon4
lrwxrwxrwx 1 root root 0 Jan 1 00:00 hwmon5 -> ../../devices/i2c-102/102-0060/hwmon/hwmon5
lrwxrwxrwx 1 root root 0 Jan 1 00:00 hwmon6 -> ../../devices/i2c-103/103-0070/hwmon/hwmon6
lrwxrwxrwx 1 root root 0 Jan 1 00:00 hwmon7 -> ../../devices/i2c-103/103-1071/hwmon/hwmon7
lrwxrwxrwx 1 root root 0 Jan 1 00:00 hwmon8 -> ../../devices/i2c-103/103-2072/hwmon/hwmon8
lrwxrwxrwx 1 root root 0 Jan 1 00:00 hwmon9 -> ../../devices/i2c-103/103-3073/hwmon/hwmon9
3. 查看pmbus设备监控数据，所有字段解释详见kernel文档。
/sys/class/hwmon # cats 'hwmon2/device/*'
# 电流监控数据 单位：mA 毫安 /1000
hwmon2/device/curr1_crit: 255000
hwmon2/device/curr1_crit_alarm: 0
hwmon2/device/curr1_input: 2679
hwmon2/device/curr1_label: iin
hwmon2/device/curr1_max: 25000
hwmon2/device/curr1_max_alarm: 0
hwmon2/device/curr2_crit: 122000
hwmon2/device/curr2_crit_alarm: 0
hwmon2/device/curr2_input: 22968
hwmon2/device/curr2_label: iout1
hwmon2/device/curr2_max: 98000
hwmon2/device/curr2_max_alarm: 0
hwmon2/device/driver: cat: read error: Is a directory
hwmon2/device/hwmon: cat: read error: Is a directory
# 电压监控数据 单位：mV 毫伏 1/1000
hwmon2/device/in1_crit: 17000
hwmon2/device/in1_crit_alarm: 0
hwmon2/device/in1_input: 11906
hwmon2/device/in1_label: vin
hwmon2/device/in2_alarm: 0
hwmon2/device/in2_input: 631
hwmon2/device/in2_label: vout1
hwmon2/device/modalias: i2c:tps53667
hwmon2/device/name: tps53667
# 功率监控数据 单位：uW 微伏 1/1000000
hwmon2/device/power1_input: 31625000
hwmon2/device/power1_label: pin
hwmon2/device/power2_input: 23343750
hwmon2/device/power2_label: pout1
hwmon2/device/subsystem: cat: read error: Is a directory
# 温度监控数据 单位：m℃ 毫摄氏度 1/1000
hwmon2/device/temp1_crit: 125000
hwmon2/device/temp1_crit_alarm: 0
hwmon2/device/temp1_input: 35500
hwmon2/device/temp1_max: 95000
hwmon2/device/temp1_max_alarm: 0
hwmon2/device/uevent: DRIVER=tps53667
MODALIAS=i2c:tps53667
4. 构造一个UV fault alarm，如下。可见异常恢复后，告警依然保持，不会清除；重启也不是清除告警；手动清除后，告警清除。
/sys/devices/i2c-103/103-3073 # cats 'in*'
in1_crit: 17000
in1_crit_alarm: 0
in1_input: 11968
in1_label: vin
in2_alarm: 0
in2_input: 0
in2_label: vout1
/sys/devices/i2c-103/103-3073 # echo 10000 > in1_crit # 将in voltage的UV fault阈值设成10V
/sys/devices/i2c-103/103-3073 # cats 'in*'
in1_crit: 10000
in1_crit_alarm: 1 # 告警触发
in1_input: 11953
in1_label: vin
in2_alarm: 0
in2_input: 0
in2_label: vout1
/sys/devices/i2c-103/103-3073 # echo 17000 > in1_crit # 将in voltage的UV fault阈值恢复成17V
/sys/devices/i2c-103/103-3073 # cats 'in*'
in1_crit: 17000
in1_crit_alarm: 1 # 异常后再恢复正常，告警依然保持
in1_input: 11968
in1_label: vin
in2_alarm: 0
in2_input: 0
in2_label: vout1
/sys/devices/i2c-103/103-3073 # reboot
。。。（启动过程省略）
/sys/devices/i2c-103/103-3073 # cats 'in*'
in1_crit: 17000
in1_crit_alarm: 1 # 重启不会清除告警
in1_input: 11968
in1_label: vin
in2_alarm: 0
in2_input: 0
in2_label: vout1
/sys/devices/i2c-103/103-3073 # echo 0 > clear_fault # 手动清除告警
/sys/devices/i2c-103/103-3073 # cats 'in*'
in1_crit: 17000
in1_crit_alarm: 0 # 告警清除
in1_input: 11968
in1_label: vin
in2_alarm: 0
in2_input: 631
in2_label: vout1
附主要数据结构：
struct pmbus_data {
struct device *dev;
struct device *hwmon_dev;
u32 flags; /* from platform data */
int exponent; /* linear mode: exponent for output voltages */
const struct pmbus_driver_info *info;
int max_attributes;
int num_attributes;
struct attribute_group group;
struct pmbus_sensor *sensors;
struct mutex update_lock;
bool valid;
unsigned long last_updated; /* in jiffies */
/*
* A single status register covers multiple attributes,
* so we keep them all together.
*/
u8 status[PB_NUM_STATUS_REG];
u8 status_register;
u8 currpage;
};
struct pmbus_driver_info {
int pages; /* Total number of pages */
enum pmbus_data_format format[PSC_NUM_CLASSES];
/*
* Support one set of coefficients for each sensor type
* Used for chips providing data in direct mode.
*/
int m[PSC_NUM_CLASSES]; /* mantissa for direct data format */
int b[PSC_NUM_CLASSES]; /* offset */
int R[PSC_NUM_CLASSES]; /* exponent */
u32 func[PMBUS_PAGES]; /* Functionality, per page */
/*
* The following functions map manufacturing specific register values
* to PMBus standard register values. Specify only if mapping is
* necessary.
* Functions return the register value (read) or zero (write) if
* successful. A return value of -ENODATA indicates that there is no
* manufacturer specific register, but that a standard PMBus register
* may exist. Any other negative return value indicates that the
* register does not exist, and that no attempt should be made to read
* the standard register.
*/
int (*read_byte_data)(struct i2c_client *client, int page, int reg);
int (*read_word_data)(struct i2c_client *client, int page, int reg);
int (*write_word_data)(struct i2c_client *client, int page, int reg,
u16 word);
int (*write_byte)(struct i2c_client *client, int page, u8 value);
/*
* The identify function determines supported PMBus functionality.
* This function is only necessary if a chip driver supports multiple
* chips, and the chip functionality is not pre-determined.
*/
int (*identify)(struct i2c_client *client,
struct pmbus_driver_info *info);
};
struct pmbus_sensor {
struct pmbus_sensor *next;
char name[PMBUS_NAME_SIZE]; /* sysfs sensor name */
struct device_attribute attribute;
u8 page; /* page number */
u16 reg; /* register */
enum pmbus_sensor_classes class; /* sensor class */
bool update; /* runtime sensor update needed */
int data; /* Sensor data.
Negative if there was a read error */
};
/*
* Virtual registers.
* Useful to support attributes which are not supported by standard PMBus
* registers but exist as manufacturer specific registers on individual chips.
* Must be mapped to real registers in device specific code.
*
* Semantics:
* Virtual registers are all word size.
* READ registers are read-only; writes are either ignored or return an error.
* RESET registers are read/write. Reading reset registers returns zero
* (used for detection), writing any value causes the associated history to be
* reset.
* Virtual registers have to be handled in device specific driver code. Chip
* driver code returns non-negative register values if a virtual register is
* supported, or a negative error code if not. The chip driver may return
* -ENODATA or any other error code in this case, though an error code other
* than -ENODATA is handled more efficiently and thus preferred. Either case,
* the calling PMBus core code will abort if the chip driver returns an error
* code when reading or writing virtual registers.
*/
#define PMBUS_VIRT_BASE 0x100
#define PMBUS_VIRT_READ_TEMP_AVG (PMBUS_VIRT_BASE + 0)
#define PMBUS_VIRT_READ_TEMP_MIN (PMBUS_VIRT_BASE + 1)
#define PMBUS_VIRT_READ_TEMP_MAX (PMBUS_VIRT_BASE + 2)
#define PMBUS_VIRT_RESET_TEMP_HISTORY (PMBUS_VIRT_BASE + 3)
#define PMBUS_VIRT_READ_VIN_AVG (PMBUS_VIRT_BASE + 4)
#define PMBUS_VIRT_READ_VIN_MIN (PMBUS_VIRT_BASE + 5)
#define PMBUS_VIRT_READ_VIN_MAX (PMBUS_VIRT_BASE + 6)
#define PMBUS_VIRT_RESET_VIN_HISTORY (PMBUS_VIRT_BASE + 7)
#define PMBUS_VIRT_READ_IIN_AVG (PMBUS_VIRT_BASE + 8)
#define PMBUS_VIRT_READ_IIN_MIN (PMBUS_VIRT_BASE + 9)
#define PMBUS_VIRT_READ_IIN_MAX (PMBUS_VIRT_BASE + 10)
#define PMBUS_VIRT_RESET_IIN_HISTORY (PMBUS_VIRT_BASE + 11)
#define PMBUS_VIRT_READ_PIN_AVG (PMBUS_VIRT_BASE + 12)
#define PMBUS_VIRT_READ_PIN_MAX (PMBUS_VIRT_BASE + 13)
#define PMBUS_VIRT_RESET_PIN_HISTORY (PMBUS_VIRT_BASE + 14)
#define PMBUS_VIRT_READ_POUT_AVG (PMBUS_VIRT_BASE + 15)
#define PMBUS_VIRT_READ_POUT_MAX (PMBUS_VIRT_BASE + 16)
#define PMBUS_VIRT_RESET_POUT_HISTORY (PMBUS_VIRT_BASE + 17)
#define PMBUS_VIRT_READ_VOUT_AVG (PMBUS_VIRT_BASE + 18)
#define PMBUS_VIRT_READ_VOUT_MIN (PMBUS_VIRT_BASE + 19)
#define PMBUS_VIRT_READ_VOUT_MAX (PMBUS_VIRT_BASE + 20)
#define PMBUS_VIRT_RESET_VOUT_HISTORY (PMBUS_VIRT_BASE + 21)
#define PMBUS_VIRT_READ_IOUT_AVG (PMBUS_VIRT_BASE + 22)
#define PMBUS_VIRT_READ_IOUT_MIN (PMBUS_VIRT_BASE + 23)
#define PMBUS_VIRT_READ_IOUT_MAX (PMBUS_VIRT_BASE + 24)
#define PMBUS_VIRT_RESET_IOUT_HISTORY (PMBUS_VIRT_BASE + 25)
#define PMBUS_VIRT_READ_TEMP2_AVG (PMBUS_VIRT_BASE + 26)
#define PMBUS_VIRT_READ_TEMP2_MIN (PMBUS_VIRT_BASE + 27)
#define PMBUS_VIRT_READ_TEMP2_MAX (PMBUS_VIRT_BASE + 28)
#define PMBUS_VIRT_RESET_TEMP2_HISTORY (PMBUS_VIRT_BASE + 29)
#define PMBUS_VIRT_READ_VMON (PMBUS_VIRT_BASE + 30)
#define PMBUS_VIRT_VMON_UV_WARN_LIMIT (PMBUS_VIRT_BASE + 31)
#define PMBUS_VIRT_VMON_OV_WARN_LIMIT (PMBUS_VIRT_BASE + 32)
#define PMBUS_VIRT_VMON_UV_FAULT_LIMIT (PMBUS_VIRT_BASE + 33)
#define PMBUS_VIRT_VMON_OV_FAULT_LIMIT (PMBUS_VIRT_BASE + 34)
#define PMBUS_VIRT_STATUS_VMON (PMBUS_VIRT_BASE + 35)