CoreSight Device Enumeration Failure on Nvidia Jetson Platforms

CoreSight Device Enumeration Failure on Nvidia Jetson Nano and AGX Xavier

The CoreSight debugging and tracing infrastructure is a critical component for developers working on ARM-based systems, enabling real-time tracing, profiling, and debugging of complex software and hardware interactions. However, when attempting to use CoreSight on Nvidia Jetson platforms such as the Jetson Nano and Jetson AGX Xavier, users may encounter an issue where the CoreSight devices are not enumerated correctly. This manifests as an empty /sys/bus/coresight/devices directory, despite having configured the kernel with CoreSight support. This issue can severely hinder debugging efforts, particularly in embedded systems where real-time tracing is essential for performance optimization and fault diagnosis.

The CoreSight framework relies on a combination of kernel configuration, device tree bindings, and hardware initialization to properly detect and expose CoreSight devices to the user space. When the /sys/bus/coresight/devices directory is empty, it indicates that the CoreSight components are either not being detected by the kernel or are not being initialized correctly. This can stem from a variety of causes, ranging from misconfigurations in the kernel build to issues with the device tree or even hardware-specific quirks.

Understanding the root cause of this issue requires a deep dive into the CoreSight architecture, the Linux kernel’s handling of CoreSight devices, and the specific implementation details of the Nvidia Jetson platforms. The following sections will explore the possible causes of this issue and provide detailed troubleshooting steps to resolve it.

Kernel Configuration and Device Tree Misalignment

One of the most common causes of CoreSight device enumeration failure is a misalignment between the kernel configuration and the device tree. The device tree is a data structure used by the Linux kernel to describe the hardware components of a system. For CoreSight devices to be detected and initialized, the device tree must include the appropriate bindings for the CoreSight components, and the kernel must be configured to support these bindings.

On Nvidia Jetson platforms, the device tree is typically provided by the vendor and includes descriptions of the system’s hardware, including the ARM cores, peripherals, and debugging interfaces. If the device tree does not include the necessary CoreSight bindings, the kernel will not be able to detect the CoreSight devices, resulting in an empty /sys/bus/coresight/devices directory. Similarly, if the kernel is not configured to support CoreSight, the device tree bindings will be ignored, and the CoreSight devices will not be enumerated.

To diagnose this issue, it is essential to verify that the kernel configuration includes the necessary options for CoreSight support. The relevant kernel configuration options include CONFIG_CORESIGHT, CONFIG_CORESIGHT_LINKS_AND_SINKS, and CONFIG_CORESIGHT_SOURCE_ETM4X, among others. These options enable the CoreSight framework, the links and sinks that route trace data, and the Embedded Trace Macrocell (ETM) for ARM Cortex-A cores, respectively. If any of these options are missing or disabled, the CoreSight devices will not be detected.

Additionally, the device tree must be inspected to ensure that it includes the appropriate CoreSight bindings. The device tree bindings for CoreSight typically include nodes for the trace funnel, replicator, and ETM components, among others. These nodes must be correctly defined and compatible with the kernel’s CoreSight driver. If the device tree is missing these nodes or contains errors, the CoreSight devices will not be enumerated.

Hardware Initialization and Platform-Specific Quirks

Another potential cause of CoreSight device enumeration failure is improper hardware initialization or platform-specific quirks. The CoreSight components on Nvidia Jetson platforms are part of the system-on-chip (SoC) and rely on proper initialization by the bootloader and kernel. If the hardware is not initialized correctly, the CoreSight components may not be accessible, leading to enumeration failure.

On Nvidia Jetson platforms, the bootloader is responsible for initializing the hardware, including the ARM cores, memory, and peripherals. If the bootloader does not initialize the CoreSight components correctly, the kernel will not be able to detect them. This can occur if the bootloader is misconfigured or if there are platform-specific quirks that affect the initialization process.

For example, some Nvidia Jetson platforms may require specific power management configurations or clock settings for the CoreSight components to function correctly. If these settings are not applied, the CoreSight components may remain in a low-power state or be otherwise inaccessible. Additionally, some platforms may have errata or hardware bugs that affect the CoreSight components, requiring workarounds in the bootloader or kernel.

To diagnose this issue, it is necessary to inspect the bootloader configuration and logs to ensure that the CoreSight components are being initialized correctly. This may involve enabling verbose logging in the bootloader or using hardware debugging tools to inspect the state of the CoreSight components during boot. Additionally, it may be necessary to consult the platform’s technical reference manual or errata documentation to identify any platform-specific quirks that could affect CoreSight initialization.

Debugging and Resolving CoreSight Enumeration Issues

Resolving CoreSight device enumeration failure on Nvidia Jetson platforms requires a systematic approach to debugging and troubleshooting. The following steps outline a detailed process for identifying and resolving the issue:

1. Verify Kernel Configuration: Begin by verifying that the kernel is configured to support CoreSight. Check the kernel configuration file (typically .config) for the presence of the necessary CoreSight options, such as CONFIG_CORESIGHT, CONFIG_CORESIGHT_LINKS_AND_SINKS, and CONFIG_CORESIGHT_SOURCE_ETM4X. If any of these options are missing or disabled, recompile the kernel with the correct configuration.

2. Inspect Device Tree Bindings: Next, inspect the device tree to ensure that it includes the appropriate CoreSight bindings. Look for nodes corresponding to CoreSight components such as the trace funnel, replicator, and ETM. Verify that these nodes are correctly defined and compatible with the kernel’s CoreSight driver. If the device tree is missing these nodes or contains errors, update the device tree accordingly.

3. Check Bootloader Initialization: Examine the bootloader configuration and logs to ensure that the CoreSight components are being initialized correctly. Look for any errors or warnings related to CoreSight initialization. If necessary, enable verbose logging in the bootloader to gather more detailed information.

4. Investigate Platform-Specific Quirks: Consult the platform’s technical reference manual and errata documentation to identify any platform-specific quirks that could affect CoreSight initialization. Look for any known issues or workarounds related to CoreSight components. If applicable, apply the necessary workarounds in the bootloader or kernel.

5. Use Hardware Debugging Tools: If the issue persists, use hardware debugging tools such as JTAG or SWD to inspect the state of the CoreSight components during boot. Verify that the CoreSight components are being powered on and initialized correctly. Look for any signs of hardware faults or misconfigurations.

6. Update Firmware and Drivers: Ensure that the bootloader, kernel, and CoreSight drivers are up to date. Check for any updates or patches from Nvidia or the ARM community that address CoreSight enumeration issues. Apply any relevant updates and re-test the system.

7. Test with a Known Good Configuration: If possible, test the system with a known good configuration, such as a reference image provided by Nvidia or a community-maintained build that includes CoreSight support. This can help isolate the issue and determine whether it is related to the specific configuration or a broader problem with the hardware or software.

By following these steps, developers can systematically diagnose and resolve CoreSight device enumeration failure on Nvidia Jetson platforms. This process requires a combination of kernel configuration, device tree inspection, bootloader analysis, and hardware debugging, but with careful attention to detail, the issue can be resolved, enabling the use of CoreSight for debugging and tracing on these powerful embedded platforms.