On Thu, Feb 17, 2022 at 2:22 AM Naveen Krishna Chatradhi <nchatrad@xxxxxxx> wrote: > > This documentation for amd_hsmp driver explains how to use the > device interface. > > Signed-off-by: Naveen Krishna Chatradhi <nchatrad@xxxxxxx> Acked-by: Song Liu <song@xxxxxxxxxx> > --- > Changes since v5: > variable name changed from buf to args > Changes since v4: > struct hsmp_message is updated > 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 | 85 ++++++++++++++++++++++++++++++++++ > 1 file changed, 85 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..9de7e028d6e3 > --- /dev/null > +++ b/Documentation/x86/amd_hsmp.rst > @@ -0,0 +1,85 @@ > +.. 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 family/model PPR > +Eg: https://www.amd.com/system/files/TechDocs/55898_B1_pub_0.50.zip > + > +HSMP interface is supported on 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 input argument words in message */ > + __u16 response_sz; /* Number of expected output/response words */ > + __u32 args[HSMP_MAX_MSG_LEN]; /* argument/response buffer */ > + __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 and message definitions can be found in chapter > +"7 Host System Management Port (HSMP)" of the respective family/model PPR > +eg: 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 >
