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Dheeraj Kumar Srivastava
fb3af1f4fe
IOMMU driver sends command to IOMMU hardware via command buffer. In cases where IOMMU hardware fails to process commands in command buffer, dumping it is a valuable input to debug the issue. IOMMU hardware processes command buffer entry at offset equals to the head pointer. Dumping just the entry at the head pointer may not always be useful. The current head may not be pointing to the entry of the command buffer which is causing the issue. IOMMU Hardware may have processed the entry and updated the head pointer. So dumping the entire command buffer gives a broad understanding of what hardware was/is doing. The command buffer dump will have all entries from start to end of the command buffer. Along with that, it will have a head and tail command buffer pointer register dump to facilitate where the IOMMU driver and hardware are in the command buffer for injecting and processing the entries respectively. Command buffer is a per IOMMU data structure. So dumping on per IOMMU basis. eg. -> To get command buffer dump for iommu<x> (say, iommu00) #cat /sys/kernel/debug/iommu/amd/iommu00/cmdbuf Signed-off-by: Dheeraj Kumar Srivastava <dheerajkumar.srivastava@amd.com> Reviewed-by: Vasant Hegde <vasant.hegde@amd.com> Link: https://lore.kernel.org/r/20250702093804.849-5-dheerajkumar.srivastava@amd.com Signed-off-by: Will Deacon <will@kernel.org>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the reStructuredText markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.