.. SPDX-License-Identifier: GPL-2.0

amd apml modules (apml_sbtsi, apml_sbrmi and apml_alert)

amd-apml: APML interface drivers for BMC

EPYC processors from AMD provide APML interface for BMC users to monitor and configure the system parameters via the Advanced Platform Management List (APML) interface defined in EPYC processor PPR.

This chapter defines custom protocols over i2c/i3c bus

• Mailbox
• CPUID [RO]
• MCA MSR {RO]
• RMI/TSI register [RW]

module_i2c_i3c based sbrmi and sbtsi modules, which are probed as i2c or i3c client devices, depending on the platforms DTS.

https://developer.amd.com/resources/epyc-resources/epyc-specifications

APMl library provides C API fo the user space application on top of this module.

Disclaimer

The amd apml modules are supported only on AMD Family 19h (including third-generation AMD EPYC processors (codenamed "Milan")) or later CPUs. Using the amd apml modules on earlier CPUs could produce unexpected results, and may cause the processor to operate outside of your motherboard or system specifications. Correspondingly, defaults to only executing on AMD Family 19h Model (0h ~ 1Fh & 30h ~ 3Fh) server line of processors.

Interface

Both apml_sbtsi and apml_sbrmi modules register a misc_device to provide ioctl interface to user space, allowing them to run these custom protocols.

apml_sbtsi module registers hwmon sensors for monitoring current temperature, managing max and min thresholds.

apml_sbrmi module registers hwmon sensors for monitoring power_cap_max, current power consumption and managing power_cap.

Build and Install

Kernel development packages for the running kernel need to be installed prior to building the amd apml modules. A Makefile is provided which should work with most kernel source trees.

To cross compile for arm based BMC

export CC=arm-openbmc-linux-gnueabi-gcc # Or similar export ARCH=arm KDIR=

To build the kernel module:

> make

To install the kernel module:

> sudo make modules_install

To clean the kernel module build directory:

> make clean

Note: There is a fix required in the upstream linux kerenl header to handle the i3c_dev. the patch is kept in patches/ folder of this repo.

Loading

If the apml modules were installed you should use the modprobe command to load the module.

> sudo modprobe apml_sbrmi apml_sbtsi

The apml modules can also be loaded using insmod if the module was not installed:

> sudo insmod ./apml_sbrmi.ko

> sudo insmod ./apml_sbtsi.ko

APML_ALERTL

Disclaimer: apml_alert module is currently experimental and may change in the future

EPYC processors from AMD provide APML ALERT_L for BMC users to monitor events.

APML Alert_L is asserted in multiple events: 1) Machine Check Exception occurs within the system 2) The processor alerts the SBI on system fatal error event 3) Set by hardware as a result of a 0x71/0x72/0x73 command completion 4) Set by firmware to indicate the completion of a mailbox operation 5) Temperature Alert

apml_alertl module defines an interface for user space to register their PID for notifications and an ISR which identifies the source of the interrupt and signals user space application.

apml_alertl module depends on apml_sbrmi module for identifying the source.

DTS node definition for Alert_L module

required:

• compatible
• status
• gpios: GPIO associated with the Alert_L of the socket
• sbrmi: Array of RMI devices on the system

Example:

/ { / Alert_L associated with socket 0 / alertl_sock0 { compatible = "apml-alertl"; status = "okay"; gpios = <&gpio0 ASPEED_GPIO(I, 7) GPIO_ACTIVE_LOW>; sbrmi = <&sbrmi_p0_1 &sbrmi_p1_1>; };

/* Alert_L associated with socket 1 */
alertl_sock1 {
    compatible = "apml-alertl";
    status = "okay";
    gpios = <&gpio0 ASPEED_GPIO(U, 4) GPIO_ACTIVE_LOW>;
    sbrmi = <&sbrmi_p1_1 &sbrmi_p0_1>;
};

};

Loading

To install apml_alertl driver builtin as module, user can use the modprobe or insmod command

> sudo modprobe apml_alertl

> sudo insmod ./apml_alertl.ko

Note: Dependency on apml_sbrmi.ko module

Unloading

> sudo rmmod apml_alertl

If the driver is inbuilt can be removed/inserted by running bind/unbind command.

> cd /sys/bus/platform/drivers/alertl

> echo alertl_rmi# > unbind/bind

USAGE

User need to register the PID of the process with the apml_alertl module, by writing the PID to the debugfs entry, /sys/kernel/debug/apml_alert/ras_fatal_pid

> echo $PID > /sys/kernel/debug/apml_alert/$alert_source

User application needs to wait for the signal from the apml_alertl module.

Signal from module carries a "struct kernel_siginfo" with following data

• si_int: is filled with the event data [15:0] = ras_status register [23:16] = rmi static address

• si_signo: 44

Currently the kernel driver send signal only in event, RAS status register bit set.

• In case of RAS fatal error the status register BIT(1) will set, and ISR clears the bit to avoid interfere with alerts during the ISR.

Future versions of the driver may include support for other events mentioned above.