Documentation/driver-api/cxl/platform/acpi/cedt.rst

Source file repositories/reference/linux-study-clean/Documentation/driver-api/cxl/platform/acpi/cedt.rst

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Documentation/driver-api/cxl/platform/acpi/cedt.rst
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Support Tooling And Documentation
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Documentation
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Support Tooling And Documentation: documentation
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Repository support layer: documentation, build tooling, samples, user-space helper tools, generated initramfs support, licenses, and validation utilities.

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.. SPDX-License-Identifier: GPL-2.0

================================
CEDT - CXL Early Discovery Table
================================

The CXL Early Discovery Table is generated by BIOS to describe the CXL memory
regions configured at boot by the BIOS.

CHBS
====
The CXL Host Bridge Structure describes CXL host bridges.  Other than describing
device register information, it reports the specific host bridge UID for this
host bridge.  These host bridge ID's will be referenced in other tables.

Example ::

          Subtable Type : 00 [CXL Host Bridge Structure]
               Reserved : 00
                 Length : 0020
 Associated host bridge : 00000007    <- Host bridge _UID
  Specification version : 00000001
               Reserved : 00000000
          Register base : 0000010370400000
        Register length : 0000000000010000

CFMWS
=====
The CXL Fixed Memory Window structure describes a memory region associated
with one or more CXL host bridges (as described by the CHBS).  It additionally
describes any inter-host-bridge interleave configuration that may have been
programmed by BIOS.

Example ::

            Subtable Type : 01 [CXL Fixed Memory Window Structure]
                 Reserved : 00
                   Length : 002C
                 Reserved : 00000000
      Window base address : 000000C050000000   <- Memory Region
              Window size : 0000003CA0000000
 Interleave Members (2^n) : 01                 <- Interleave configuration
    Interleave Arithmetic : 00
                 Reserved : 0000
              Granularity : 00000000
             Restrictions : 0006
                    QtgId : 0001
             First Target : 00000007           <- Host Bridge _UID
              Next Target : 00000006           <- Host Bridge _UID

The restriction field dictates what this SPA range may be used for (memory type,
voltile vs persistent, etc). One or more bits may be set. ::

  Bit[0]: CXL Type 2 Memory
  Bit[1]: CXL Type 3 Memory
  Bit[2]: Volatile Memory
  Bit[3]: Persistent Memory
  Bit[4]: Fixed Config (HPA cannot be reused)

INTRA-host-bridge interleave (multiple devices on one host bridge) is NOT
reported in this structure, and is solely defined via CXL device decoder
programming (host bridge and endpoint decoders).

Annotation

Implementation Notes