Documentation/driver-api/cxl: BIOS/EFI expectation update

Add a snippet about what Linux expects BIOS/EFI to do (and not
to do) to the BIOS/EFI section.

Suggested-by: Alejandro Lucero Palau <alucerop@amd.com>
Signed-off-by: Gregory Price <gourry@gourry.net>
Reviewed-by: Dave Jiang <dave.jiang@intel.com>
Reviewed-by: Alejandro Lucero Palau <alucerop@amd.com>
Reviewed-by: Jonathan Cameron <jonathan.cameron@huawei.com>
Link: https://patch.msgid.link/20251219170538.1675743-2-gourry@gourry.net
Signed-off-by: Dave Jiang <dave.jiang@intel.com>

diff --git a/Documentation/driver-api/cxl/platform/bios-and-efi.rst b/Documentation/driver-api/cxl/platform/bios-and-efi.rst
index a9aa0ccd92af7e409e5dae7fc7a9abaf0b15e890..9034c206cf8e27d674ca3e916885516089d3226d 100644 (file)
--- a/Documentation/driver-api/cxl/platform/bios-and-efi.rst
+++ b/Documentation/driver-api/cxl/platform/bios-and-efi.rst
@@ -29,6 +29,26 @@ at :doc:`ACPI Tables <acpi>`.
    on physical memory region size and alignment, memory holes, HDM interleave,
    and what linux expects of HDM decoders trying to work with these features.
 
+
+Linux Expectations of BIOS/EFI Software
+=======================================
+Linux expects BIOS/EFI software to construct sufficient ACPI tables (such as
+CEDT, SRAT, HMAT, etc) and platform-specific configurations (such as HPA spaces
+and host-bridge interleave configurations) to allow the Linux driver to
+subsequently configure the devices in the CXL fabric at runtime.
+
+Programming of HDM decoders and switch ports is not required, and may be
+deferred to the CXL driver based on admin policy (e.g. udev rules).
+
+Some platforms may require pre-programming HDM decoders and locking them
+due to quirks (see: Zen5 address translation), but this is not the normal,
+"expected" configuration path.  This should be avoided if possible.
+
+Some platforms may wish to pre-configure these resources to bring memory
+up without requiring CXL driver support.  These platform vendors should
+test their configurations with the existing CXL driver and provide driver
+support for their auto-configurations if features like RAS are required.
+
 UEFI Settings
 =============
 If your platform supports it, the :code:`uefisettings` command can be used to