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Add basic ACPI table information needed to understand the CXL driver probe process. Signed-off-by: Gregory Price <gourry@gourry.net> Reviewed-by: Dave Jiang <dave.jiang@intel.com> Link: https://patch.msgid.link/20250512162134.3596150-6-gourry@gourry.net Signed-off-by: Dave Jiang <dave.jiang@intel.com>
77 lines
2.4 KiB
ReStructuredText
77 lines
2.4 KiB
ReStructuredText
.. SPDX-License-Identifier: GPL-2.0
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===========
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ACPI Tables
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===========
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ACPI is the "Advanced Configuration and Power Interface", which is a standard
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that defines how platforms and OS manage power and configure computer hardware.
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For the purpose of this theory of operation, when referring to "ACPI" we will
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usually refer to "ACPI Tables" - which are the way a platform (BIOS/EFI)
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communicates static configuration information to the operation system.
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The Following ACPI tables contain *static* configuration and performance data
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about CXL devices.
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.. toctree::
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:maxdepth: 1
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acpi/cedt.rst
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acpi/srat.rst
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acpi/hmat.rst
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acpi/slit.rst
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acpi/dsdt.rst
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The SRAT table may also contain generic port/initiator content that is intended
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to describe the generic port, but not information about the rest of the path to
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the endpoint.
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Linux uses these tables to configure kernel resources for statically configured
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(by BIOS/EFI) CXL devices, such as:
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- NUMA nodes
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- Memory Tiers
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- NUMA Abstract Distances
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- SystemRAM Memory Regions
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- Weighted Interleave Node Weights
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ACPI Debugging
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==============
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The :code:`acpidump -b` command dumps the ACPI tables into binary format.
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The :code:`iasl -d` command disassembles the files into human readable format.
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Example :code:`acpidump -b && iasl -d cedt.dat` ::
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[000h 0000 4] Signature : "CEDT" [CXL Early Discovery Table]
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Common Issues
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-------------
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Most failures described here result in a failure of the driver to surface
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memory as a DAX device and/or kmem.
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* CEDT CFMWS targets list UIDs do not match CEDT CHBS UIDs.
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* CEDT CFMWS targets list UIDs do not match DSDT CXL Host Bridge UIDs.
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* CEDT CFMWS Restriction Bits are not correct.
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* CEDT CFMWS Memory regions are poorly aligned.
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* CEDT CFMWS Memory regions spans a platform memory hole.
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* CEDT CHBS UIDs do not match DSDT CXL Host Bridge UIDs.
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* CEDT CHBS Specification version is incorrect.
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* SRAT is missing regions described in CEDT CFMWS.
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* Result: failure to create a NUMA node for the region, or
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region is placed in wrong node.
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* HMAT is missing data for regions described in CEDT CFMWS.
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* Result: NUMA node being placed in the wrong memory tier.
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* SLIT has bad data.
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* Result: Lots of performance mechanisms in the kernel will be very unhappy.
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All of these issues will appear to users as if the driver is failing to
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support CXL - when in reality they are all the failure of a platform to
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configure the ACPI tables correctly.
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