Investigating Device 18 (0000:00:18.x)

Objective

The goal of this exercise is to investigate the most populated address, specifically device 18 (0000:00:18.x), and gather all available information about it. Since we do not have a pci_watcher implemented yet, we will rely on system interfaces such as /sys and /proc to extract the necessary details.

Step 1: Identify the Device in /sys

The /sys filesystem provides a hierarchical view of devices, including PCI devices. For device 0000:00:18.x, we can explore the corresponding directory in /sys.

Path to Device 18 in /sys:

/sys/bus/pci/devices/0000:00:18.x

Replace x with the function numbers (0 through 7) to explore each function of device 18.

Step 2: Gather Information from /sys

Here are the key files and directories to inspect for each function of device 18:

  1. Vendor and Device IDs:

    • File: vendor

    • File: device

    • These files contain the vendor ID and device ID in hexadecimal format. For example: - vendor might contain 0x1022 (AMD). - device might contain a specific device ID for the host bridge.

  2. Class Code:

    • File: class

    • This file contains the device class code, which indicates the type of device (e.g., host bridge, PCI bridge, etc.).

  3. Configuration Space:

    • File: config

    • This binary file contains the raw PCI configuration space for the device. Tools like lspci -xxxx or hexdump can be used to inspect it.

  4. Resource Allocation:

    • File: resource

    • This file contains the memory and I/O resources allocated to the device.

    • Files: resource0, resource1, etc. - These files represent the actual memory or I/O regions allocated to the device.

  5. Driver Information:

    • Symlink: driver

    • This symlink points to the driver currently bound to the device (if any).

  6. Power Management:

    • Directory: power/

    • Contains information about the device’s power state (e.g., control, runtime_status).

  7. Device-specific Attributes:

    • Directory: device/

    • Contains device-specific attributes and configuration options.

Step 3: Gather Information from /proc

The /proc filesystem provides additional system-wide information. For PCI devices, the following files are particularly useful:

  1. PCI Device List:

    • File: /proc/bus/pci/devices

    • This file lists all PCI devices in the system, along with their bus, device, function, and resource information.

  2. Interrupts:

    • File: /proc/interrupts

    • This file lists interrupt usage across the system. Look for entries related to device 18 to determine if it uses interrupts.

  3. I/O Memory and Ports:

    • File: /proc/ioports

    • Lists I/O port ranges used by devices.

    • File: /proc/iomem

    • Lists memory ranges used by devices.

Step 4: Investigate Device 18 Functions

Since device 18 has multiple functions (0 through 7), we need to investigate each one individually. Here’s how we can approach it:

  1. Function 0 (0000:00:18.0):

    • Check vendor, device, and class to confirm it’s a host bridge.

    • Inspect resource to see memory and I/O allocations.

    • Check if a driver is bound to it (driver symlink).

  2. Function 1 (0000:00:18.1):

    • Repeat the same steps as above.

    • Compare the class and resource files to see if it differs from function 0.

  3. Functions 2-7 (0000:00:18.2 - 0000:00:18.7):

    • Investigate each function similarly.

    • Look for differences in class, resource, and driver binding.

Step 5: Use Tools to Extract Information

To make this process easier, we can use tools like lspci, setpci, and hexdump to extract and interpret information.

  1. lspci:

    • Command: lspci -v -s 0000:00:18.x

    • This will show detailed information about the device, including its class, vendor, device ID, and resource allocation.

  2. setpci:

    • Command: setpci -s 0000:00:18.x

    • This allows us to read and write directly to the PCI configuration space.

  3. hexdump:

    • Command: hexdump -C /sys/bus/pci/devices/0000:00:18.x/config

    • This will dump the raw PCI configuration space for inspection.

Step 6: Analyze the Findings

Once we’ve gathered all the information, we can analyze it to determine:

  • The exact role of each function of device 18.

  • Whether the device is a host bridge, PCI bridge, or something else.

  • How the device is configured (memory ranges, interrupts, etc.).

  • Whether the device is properly initialized and bound to a driver.

Example Investigation for Function 0 (0000:00:18.0):

  1. Check Vendor and Device IDs:

    • cat /sys/bus/pci/devices/0000:00:18.0/vendor → 0x1022 (AMD).

    • cat /sys/bus/pci/devices/0000:00:18.0/device → 0x1450.

  2. Check Class Code:

    • cat /sys/bus/pci/devices/0000:00:18.0/class → 0x060000 (Host bridge).

  3. Check Resource Allocation:

    • cat /sys/bus/pci/devices/0000:00:18.0/resource → Memory ranges and I/O ports.

  4. Check Driver Binding:

    • ls -l /sys/bus/pci/devices/0000:00:18.0/driver → Symlink to the bound driver (if any).

Next Steps:

  • Repeat the above steps for all functions of device 18 (0000:00:18.0 through 0000:00:18.7).

  • Compare the findings to understand the purpose of each function.

  • Document the results and share them for further analysis.

Let me know if you need help with specific commands or interpreting the data!