1 .. SPDX-License-Identifier: GPL-2.0
2
3 ============================================
4 AMD HSMP interface
5 ============================================
6
7 Newer Fam19h EPYC server line of processors from AMD support system
8 management functionality via HSMP (Host System Management Port).
9
10 The Host System Management Port (HSMP) is an interface to provide
11 OS-level software with access to system management functions via a
12 set of mailbox registers.
13
14 More details on the interface can be found in chapter
15 "7 Host System Management Port (HSMP)" of the family/model PPR
16 Eg: https://www.amd.com/content/dam/amd/en/documents/epyc-technical-docs/programmer-references/55898_B1_pub_0_50.zip
17
18
19 HSMP interface is supported on EPYC server CPU models only.
20
21
22 HSMP device
23 ============================================
24
25 amd_hsmp driver under the drivers/platforms/x86/ creates miscdevice
26 /dev/hsmp to let user space programs run hsmp mailbox commands.
27
28 $ ls -al /dev/hsmp
29 crw-r--r-- 1 root root 10, 123 Jan 21 21:41 /dev/hsmp
30
31 Characteristics of the dev node:
32 * Write mode is used for running set/configure commands
33 * Read mode is used for running get/status monitor commands
34
35 Access restrictions:
36 * Only root user is allowed to open the file in write mode.
37 * The file can be opened in read mode by all the users.
38
39 In-kernel integration:
40 * Other subsystems in the kernel can use the exported transport
41 function hsmp_send_message().
42 * Locking across callers is taken care by the driver.
43
44
45 HSMP sysfs interface
46 ====================
47
48 1. Metrics table binary sysfs
49
50 AMD MI300A MCM provides GET_METRICS_TABLE message to retrieve
51 most of the system management information from SMU in one go.
52
53 The metrics table is made available as hexadecimal sysfs binary file
54 under per socket sysfs directory created at
55 /sys/devices/platform/amd_hsmp/socket%d/metrics_bin
56
57 Note: lseek() is not supported as entire metrics table is read.
58
59 Metrics table definitions will be documented as part of Public PPR.
60 The same is defined in the amd_hsmp.h header.
61
62
63 An example
64 ==========
65
66 To access hsmp device from a C program.
67 First, you need to include the headers::
68
69 #include <linux/amd_hsmp.h>
70
71 Which defines the supported messages/message IDs.
72
73 Next thing, open the device file, as follows::
74
75 int file;
76
77 file = open("/dev/hsmp", O_RDWR);
78 if (file < 0) {
79 /* ERROR HANDLING; you can check errno to see what went wrong */
80 exit(1);
81 }
82
83 The following IOCTL is defined:
84
85 ``ioctl(file, HSMP_IOCTL_CMD, struct hsmp_message *msg)``
86 The argument is a pointer to a::
87
88 struct hsmp_message {
89 __u32 msg_id; /* Message ID */
90 __u16 num_args; /* Number of input argument words in message */
91 __u16 response_sz; /* Number of expected output/response words */
92 __u32 args[HSMP_MAX_MSG_LEN]; /* argument/response buffer */
93 __u16 sock_ind; /* socket number */
94 };
95
96 The ioctl would return a non-zero on failure; you can read errno to see
97 what happened. The transaction returns 0 on success.
98
99 More details on the interface and message definitions can be found in chapter
100 "7 Host System Management Port (HSMP)" of the respective family/model PPR
101 eg: https://www.amd.com/content/dam/amd/en/documents/epyc-technical-docs/programmer-references/55898_B1_pub_0_50.zip
102
103 User space C-APIs are made available by linking against the esmi library,
104 which is provided by the E-SMS project https://www.amd.com/en/developer/e-sms.html.
105 See: https://github.com/amd/esmi_ib_library
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