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