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iommu/amd: Add documentation for AMD IOMMU debugfs support
Add documentation describing how to use AMD IOMMU debugfs support to dump IOMMU data structures - IRT table, Device table, Registers (MMIO and Capability) and command buffer. Signed-off-by: Dheeraj Kumar Srivastava <[email protected]> Reviewed-by: Vasant Hegde <[email protected]> Link: https://lore.kernel.org/r/[email protected] Signed-off-by: Will Deacon <[email protected]>
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‎Documentation/ABI/testing/debugfs-amd-iommu

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What: /sys/kernel/debug/iommu/amd/iommu<x>/mmio
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Date: January 2025
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Contact: Dheeraj Kumar Srivastava <[email protected]>
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Description:
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This file provides read/write access for user input. Users specify the
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MMIO register offset for iommu<x>, and the file outputs the corresponding
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MMIO register value of iommu<x>
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Example:
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$ echo "0x18" > /sys/kernel/debug/iommu/amd/iommu00/mmio
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$ cat /sys/kernel/debug/iommu/amd/iommu00/mmio
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Output:
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Offset:0x18 Value:0x000c22000003f48d
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What: /sys/kernel/debug/iommu/amd/iommu<x>/capability
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Date: January 2025
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Contact: Dheeraj Kumar Srivastava <[email protected]>
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Description:
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This file provides read/write access for user input. Users specify the
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capability register offset for iommu<x>, and the file outputs the
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corresponding capability register value of iommu<x>.
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Example:
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$ echo "0x10" > /sys/kernel/debug/iommu/amd/iommu00/capability
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$ cat /sys/kernel/debug/iommu/amd/iommu00/capability
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Output:
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Offset:0x10 Value:0x00203040
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What: /sys/kernel/debug/iommu/amd/iommu<x>/cmdbuf
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Date: January 2025
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Contact: Dheeraj Kumar Srivastava <[email protected]>
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Description:
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This file is a read-only output file containing iommu<x> command
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buffer entries.
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Examples:
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$ cat /sys/kernel/debug/iommu/amd/iommu<x>/cmdbuf
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Output:
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CMD Buffer Head Offset:339 Tail Offset:339
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0: 00835001 10000001 00003c00 00000000
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1: 00000000 30000005 fffff003 7fffffff
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2: 00835001 10000001 00003c01 00000000
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3: 00000000 30000005 fffff003 7fffffff
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4: 00835001 10000001 00003c02 00000000
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5: 00000000 30000005 fffff003 7fffffff
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6: 00835001 10000001 00003c03 00000000
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7: 00000000 30000005 fffff003 7fffffff
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8: 00835001 10000001 00003c04 00000000
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9: 00000000 30000005 fffff003 7fffffff
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10: 00835001 10000001 00003c05 00000000
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11: 00000000 30000005 fffff003 7fffffff
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[...]
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What: /sys/kernel/debug/iommu/amd/devid
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Date: January 2025
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Contact: Dheeraj Kumar Srivastava <[email protected]>
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Description:
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This file provides read/write access for user input. Users specify the
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device ID, which can be used to dump IOMMU data structures such as the
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interrupt remapping table and device table.
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Example:
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1.
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$ echo 0000:01:00.0 > /sys/kernel/debug/iommu/amd/devid
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$ cat /sys/kernel/debug/iommu/amd/devid
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Output:
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0000:01:00.0
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2.
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$ echo 01:00.0 > /sys/kernel/debug/iommu/amd/devid
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$ cat /sys/kernel/debug/iommu/amd/devid
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Output:
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0000:01:00.0
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What: /sys/kernel/debug/iommu/amd/devtbl
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Date: January 2025
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Contact: Dheeraj Kumar Srivastava <[email protected]>
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Description:
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This file is a read-only output file containing the device table entry
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for the device ID provided in /sys/kernel/debug/iommu/amd/devid.
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Example:
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$ cat /sys/kernel/debug/iommu/amd/devtbl
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Output:
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DeviceId QWORD[3] QWORD[2] QWORD[1] QWORD[0] iommu
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0000:01:00.0 0000000000000000 20000001373b8013 0000000000000038 6000000114d7b603 iommu3
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What: /sys/kernel/debug/iommu/amd/irqtbl
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Date: January 2025
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Contact: Dheeraj Kumar Srivastava <[email protected]>
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Description:
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This file is a read-only output file containing valid IRT table entries
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for the device ID provided in /sys/kernel/debug/iommu/amd/devid.
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Example:
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$ cat /sys/kernel/debug/iommu/amd/irqtbl
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Output:
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DeviceId 0000:01:00.0
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IRT[0000] 0000000000000020 0000000000000241
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IRT[0001] 0000000000000020 0000000000000841
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IRT[0002] 0000000000000020 0000000000002041
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IRT[0003] 0000000000000020 0000000000008041
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IRT[0004] 0000000000000020 0000000000020041
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IRT[0005] 0000000000000020 0000000000080041
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IRT[0006] 0000000000000020 0000000000200041
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IRT[0007] 0000000000000020 0000000000800041
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[...]

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