This documentation for amd_hsmp driver explains how to use the device interface. Signed-off-by: Naveen Krishna Chatradhi <nchatrad@xxxxxxx> --- Changes since v3: remove change ids Changes since v2: Add statement saying the HSMP interface is supported only on server cpu models from AMD. Changes since v1: None Documentation/x86/amd_hsmp.rst | 86 ++++++++++++++++++++++++++++++++++ 1 file changed, 86 insertions(+) create mode 100644 Documentation/x86/amd_hsmp.rst diff --git a/Documentation/x86/amd_hsmp.rst b/Documentation/x86/amd_hsmp.rst new file mode 100644 index 000000000000..5dc2619ec3f0 --- /dev/null +++ b/Documentation/x86/amd_hsmp.rst @@ -0,0 +1,86 @@ +.. SPDX-License-Identifier: GPL-2.0 + +============================================ +AMD HSMP interface +============================================ + +Newer Fam19h EPYC server line of processors from AMD support system +management functionality via HSMP (Host System Management Port). + +The Host System Management Port (HSMP) is an interface to provide +OS-level software with access to system management functions via a +set of mailbox registers. + +More details on the interface can be found in chapter +"7 Host System Management Port (HSMP)" of the following PPR +https://www.amd.com/system/files/TechDocs/55898_B1_pub_0.50.zip + +HSMP interface is supported on AMD EPYC server CPU models only. + + +HSMP device +============================================ + +amd_hsmp driver under the drivers/platforms/x86/ creates miscdevice +/dev/hsmp to let user space programs run hsmp mailbox commands. + +$ ls -al /dev/hsmp +crw-r--r-- 1 root root 10, 123 Jan 21 21:41 /dev/hsmp + +Characteristics of the dev node: + * Write mode is used for running set/configure commands + * Read mode is used for running get/status monitor commands + +Access restrictions: + * Only root user is allowed to open the file in write mode. + * The file can be opened in read mode by all the users. + +In-kernel integration: + * Other subsystems in the kernel can use the exported transport + function hsmp_send_message(). + * Locking across callers is taken care by the driver. + + +An example +========== + +To access hsmp device from a C program. +First, you need to include the headers:: + + #include <linux/amd_hsmp.h> +Which defines the supported messages/message IDs. + +Next thing, open the device file, as follows:: + + int file; + + file = open("/dev/hsmp", O_RDWR); + if (file < 0) { + /* ERROR HANDLING; you can check errno to see what went wrong */ + exit(1); + } + +The following IOCTL is defined: + +``ioctl(file, HSMP_IOCTL_CMD, struct hsmp_message *msg)`` + The argument is a pointer to a:: + + struct hsmp_message { + __u32 msg_id; /* Message ID */ + __u16 num_args; /* Number of arguments in message */ + __u16 response_sz; /* Number of expected response words */ + __u32 args[HSMP_MAX_MSG_LEN]; /* Argument(s) */ + __u32 response[HSMP_MAX_MSG_LEN]; /* Response word(s) */ + __u16 sock_ind; /* socket number */ + }; + +The ioctl would return a non-zero on failure; you can read errno to see +what happened. The transaction returns 0 on success. + +More details on the interface can be found in chapter +"7 Host System Management Port (HSMP)" of the following PPR +https://www.amd.com/system/files/TechDocs/55898_B1_pub_0.50.zip + +User space C-APIs are made available by linking against the esmi library, +which is provided by the E-SMS project https://developer.amd.com/e-sms/. +See: https://github.com/amd/esmi_ib_library -- 2.17.1
