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iommu/amd: Add documentation for AMD IOMMU debugfs support

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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 <dheerajkumar.srivastava@amd.com>
Reviewed-by: Vasant Hegde <vasant.hegde@amd.com>
Link: https://lore.kernel.org/r/20250702093804.849-9-dheerajkumar.srivastava@amd.com
Signed-off-by: Will Deacon <will@kernel.org>
This commit is contained in:
Dheeraj Kumar Srivastava 2025-07-02 15:08:04 +05:30 • committed by Will Deacon
parent 349ad6d526
commit 39215bb3b0
1 changed files with 114 additions and 0 deletions
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What: /sys/kernel/debug/iommu/amd/iommu<x>/mmio
Date: January 2025
Contact: Dheeraj Kumar Srivastava <dheerajkumar.srivastava@amd.com>
Description:
This file provides read/write access for user input. Users specify the
MMIO register offset for iommu<x>, and the file outputs the corresponding
MMIO register value of iommu<x>
Example:
$ echo "0x18" > /sys/kernel/debug/iommu/amd/iommu00/mmio
$ cat /sys/kernel/debug/iommu/amd/iommu00/mmio
Output:
Offset:0x18 Value:0x000c22000003f48d
What: /sys/kernel/debug/iommu/amd/iommu<x>/capability
Date: January 2025
Contact: Dheeraj Kumar Srivastava <dheerajkumar.srivastava@amd.com>
Description:
This file provides read/write access for user input. Users specify the
capability register offset for iommu<x>, and the file outputs the
corresponding capability register value of iommu<x>.
Example:
$ echo "0x10" > /sys/kernel/debug/iommu/amd/iommu00/capability
$ cat /sys/kernel/debug/iommu/amd/iommu00/capability
Output:
Offset:0x10 Value:0x00203040
What: /sys/kernel/debug/iommu/amd/iommu<x>/cmdbuf
Date: January 2025
Contact: Dheeraj Kumar Srivastava <dheerajkumar.srivastava@amd.com>
Description:
This file is a read-only output file containing iommu<x> command
buffer entries.
Examples:
$ cat /sys/kernel/debug/iommu/amd/iommu<x>/cmdbuf
Output:
CMD Buffer Head Offset:339 Tail Offset:339
0: 00835001 10000001 00003c00 00000000
1: 00000000 30000005 fffff003 7fffffff
2: 00835001 10000001 00003c01 00000000
3: 00000000 30000005 fffff003 7fffffff
4: 00835001 10000001 00003c02 00000000
5: 00000000 30000005 fffff003 7fffffff
6: 00835001 10000001 00003c03 00000000
7: 00000000 30000005 fffff003 7fffffff
8: 00835001 10000001 00003c04 00000000
9: 00000000 30000005 fffff003 7fffffff
10: 00835001 10000001 00003c05 00000000
11: 00000000 30000005 fffff003 7fffffff
[...]
What: /sys/kernel/debug/iommu/amd/devid
Date: January 2025
Contact: Dheeraj Kumar Srivastava <dheerajkumar.srivastava@amd.com>
Description:
This file provides read/write access for user input. Users specify the
device ID, which can be used to dump IOMMU data structures such as the
interrupt remapping table and device table.
Example:
1.
$ echo 0000:01:00.0 > /sys/kernel/debug/iommu/amd/devid
$ cat /sys/kernel/debug/iommu/amd/devid
Output:
0000:01:00.0
2.
$ echo 01:00.0 > /sys/kernel/debug/iommu/amd/devid
$ cat /sys/kernel/debug/iommu/amd/devid
Output:
0000:01:00.0
What: /sys/kernel/debug/iommu/amd/devtbl
Date: January 2025
Contact: Dheeraj Kumar Srivastava <dheerajkumar.srivastava@amd.com>
Description:
This file is a read-only output file containing the device table entry
for the device ID provided in /sys/kernel/debug/iommu/amd/devid.
Example:
$ cat /sys/kernel/debug/iommu/amd/devtbl
Output:
DeviceId QWORD[3] QWORD[2] QWORD[1] QWORD[0] iommu
0000:01:00.0 0000000000000000 20000001373b8013 0000000000000038 6000000114d7b603 iommu3
What: /sys/kernel/debug/iommu/amd/irqtbl
Date: January 2025
Contact: Dheeraj Kumar Srivastava <dheerajkumar.srivastava@amd.com>
Description:
This file is a read-only output file containing valid IRT table entries
for the device ID provided in /sys/kernel/debug/iommu/amd/devid.
Example:
$ cat /sys/kernel/debug/iommu/amd/irqtbl
Output:
DeviceId 0000:01:00.0
IRT[0000] 0000000000000020 0000000000000241
IRT[0001] 0000000000000020 0000000000000841
IRT[0002] 0000000000000020 0000000000002041
IRT[0003] 0000000000000020 0000000000008041
IRT[0004] 0000000000000020 0000000000020041
IRT[0005] 0000000000000020 0000000000080041
IRT[0006] 0000000000000020 0000000000200041
IRT[0007] 0000000000000020 0000000000800041
[...]