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Alison Schofield dc18117049 cxl/region: Introduce SPA to DPA address translation
Add infrastructure to translate System Physical Addresses (SPA) to
Device Physical Addresses (DPA) within CXL regions. This capability
will be used by follow-on patches that add poison inject and clear
operations at the region level.

The SPA-to-DPA translation process follows these steps:
1. Apply root decoder transformations (SPA to HPA) if configured.
2. Extract the position in region interleave from the HPA offset.
3. Extract the DPA offset from the HPA offset.
4. Use position to find endpoint decoder.
5. Use endpoint decoder to find memdev and calculate DPA from offset.
6. Return the result - a memdev and a DPA.

It is Step 1 above that makes this a driver level operation and not
work we can push to user space. Rather than exporting the XOR maps for
root decoders configured with XOR interleave, the driver performs this
complex calculation for the user.

Steps 2 and 3 follow the CXL Spec 3.2 Section 8.2.4.20.13
Implementation Note: Device Decode Logic.

These calculations mirror much of the logic introduced earlier in DPA
to SPA translation, see cxl_dpa_to_hpa(), where the driver needed to
reverse the spec defined 'Device Decode Logic'.

Signed-off-by: Alison Schofield <alison.schofield@intel.com>
Reviewed-by: Jonathan Cameron <jonathan.cameron@huawei.com>
Link: https://patch.msgid.link/422f0e27742c6ca9a11f7cd83e6ba9fa1a8d0c74.1754290144.git.alison.schofield@intel.com
Signed-off-by: Dave Jiang <dave.jiang@intel.com>
History 2025-08-12 16:02:00 -07:00
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README

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.