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[96.255.20.138]) by smtp.gmail.com with ESMTPSA id af79cd13be357-8c096787536sm223197185a.4.2025.12.19.09.06.20 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 19 Dec 2025 09:06:20 -0800 (PST) From: Gregory Price To: linux-cxl@vger.kernel.org Cc: linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, kernel-team@meta.com, dave@stgolabs.net, jonathan.cameron@huawei.com, dave.jiang@intel.com, alison.schofield@intel.com, vishal.l.verma@intel.com, ira.weiny@intel.com, dan.j.williams@intel.com, corbet@lwn.net, gourry@gourry.net, rakuram.e96@gmail.com, alucerop@amd.com Subject: [PATCH v3 1/2] Documentation/driver-api/cxl: BIOS/EFI expectation update Date: Fri, 19 Dec 2025 12:05:37 -0500 Message-ID: <20251219170538.1675743-2-gourry@gourry.net> X-Mailer: git-send-email 2.52.0 In-Reply-To: <20251219170538.1675743-1-gourry@gourry.net> References: <20251219170538.1675743-1-gourry@gourry.net> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" 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 Signed-off-by: Gregory Price Reviewed-by: Alejandro Lucero Palau Reviewed-by: Dave Jiang Reviewed-by: Jonathan Cameron --- .../driver-api/cxl/platform/bios-and-efi.rst | 20 +++++++++++++++++++ 1 file changed, 20 insertions(+) diff --git a/Documentation/driver-api/cxl/platform/bios-and-efi.rst b/Docum= entation/driver-api/cxl/platform/bios-and-efi.rst index a9aa0ccd92af..9034c206cf8e 100644 --- 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 `. on physical memory region size and alignment, memory holes, HDM interle= ave, and what linux expects of HDM decoders trying to work with these featur= es. =20 + +Linux Expectations of BIOS/EFI Software +=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D +Linux expects BIOS/EFI software to construct sufficient ACPI tables (such = as +CEDT, SRAT, HMAT, etc) and platform-specific configurations (such as HPA s= paces +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 =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D If your platform supports it, the :code:`uefisettings` command can be used= to --=20 2.52.0