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- This document provides AMD side band IOCTL description defined for APML and its usage. Multiple AMD custom protocols defined for side band system management uses this IOCTL. User space C-APIs are made available by esmi_oob_library [1], which is provided by the E-SMS project [2]. Link: https://github.com/amd/esmi_oob_library [1] Link: https://www.amd.com/en/developer/e-sms.html [2] Reviewed-by: Naveen Krishna Chatradhi <naveenkrishna.chatradhi@amd.com> Signed-off-by: Akshay Gupta <akshay.gupta@amd.com> Link: https://lore.kernel.org/r/20250428063034.2145566-11-akshay.gupta@amd.com Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
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100 lines
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.. SPDX-License-Identifier: GPL-2.0
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=======================
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AMD SIDE BAND interface
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=======================
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Some AMD Zen based processors supports system management
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functionality via side-band interface (SBI) called
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Advanced Platform Management Link (APML). APML is an I2C/I3C
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based 2-wire processor target interface. APML is used to
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communicate with the Remote Management Interface
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(SB Remote Management Interface (SB-RMI)
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and SB Temperature Sensor Interface (SB-TSI)).
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More details on the interface can be found in chapter
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"5 Advanced Platform Management Link (APML)" of the family/model PPR [1]_.
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.. [1] https://www.amd.com/content/dam/amd/en/documents/epyc-technical-docs/programmer-references/55898_B1_pub_0_50.zip
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SBRMI device
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============
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apml_sbrmi driver under the drivers/misc/amd-sbi creates miscdevice
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/dev/sbrmi-* to let user space programs run APML mailbox, CPUID,
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MCAMSR and register xfer commands.
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Register sets is common across APML protocols. IOCTL is providing synchronization
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among protocols as transactions may create race condition.
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$ ls -al /dev/sbrmi-3c
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crw------- 1 root root 10, 53 Jul 10 11:13 /dev/sbrmi-3c
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apml_sbrmi driver registers hwmon sensors for monitoring power_cap_max,
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current power consumption and managing power_cap.
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Characteristics of the dev node:
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* Differnet xfer protocols are defined:
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* Mailbox
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* CPUID
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* MCA_MSR
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* Register xfer
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Access restrictions:
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* Only root user is allowed to open the file.
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* APML Mailbox messages and Register xfer access are read-write,
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* CPUID and MCA_MSR access is read-only.
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Driver IOCTLs
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=============
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.. c:macro:: SBRMI_IOCTL_MBOX_CMD
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.. kernel-doc:: include/uapi/misc/amd-apml.h
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:doc: SBRMI_IOCTL_MBOX_CMD
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.. c:macro:: SBRMI_IOCTL_CPUID_CMD
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.. kernel-doc:: include/uapi/misc/amd-apml.h
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:doc: SBRMI_IOCTL_CPUID_CMD
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.. c:macro:: SBRMI_IOCTL_MCAMSR_CMD
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.. kernel-doc:: include/uapi/misc/amd-apml.h
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:doc: SBRMI_IOCTL_MCAMSR_CMD
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.. c:macro:: SBRMI_IOCTL_REG_XFER_CMD
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.. kernel-doc:: include/uapi/misc/amd-apml.h
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:doc: SBRMI_IOCTL_REG_XFER_CMD
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User-space usage
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================
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To access side band interface from a C program.
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First, user need to include the headers::
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#include <uapi/misc/amd-apml.h>
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Which defines the supported IOCTL and data structure to be passed
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from the user space.
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Next thing, open the device file, as follows::
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int file;
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file = open("/dev/sbrmi-*", O_RDWR);
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if (file < 0) {
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/* ERROR HANDLING */
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exit(1);
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}
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The following IOCTLs are defined:
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``#define SB_BASE_IOCTL_NR 0xF9``
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``#define SBRMI_IOCTL_MBOX_CMD _IOWR(SB_BASE_IOCTL_NR, 0, struct apml_mbox_msg)``
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``#define SBRMI_IOCTL_CPUID_CMD _IOWR(SB_BASE_IOCTL_NR, 1, struct apml_cpuid_msg)``
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``#define SBRMI_IOCTL_MCAMSR_CMD _IOWR(SB_BASE_IOCTL_NR, 2, struct apml_mcamsr_msg)``
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``#define SBRMI_IOCTL_REG_XFER_CMD _IOWR(SB_BASE_IOCTL_NR, 3, struct apml_reg_xfer_msg)``
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User space C-APIs are made available by esmi_oob_library, hosted at
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[2]_ which is provided by the E-SMS project [3]_.
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.. [2] https://github.com/amd/esmi_oob_library
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.. [3] https://www.amd.com/en/developer/e-sms.html
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