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header.from=amd.com; Received: from DM6PR12MB4202.namprd12.prod.outlook.com (2603:10b6:5:219::22) by DM4PR12MB6398.namprd12.prod.outlook.com (2603:10b6:8:b5::19) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.9434.8; Sat, 20 Dec 2025 06:53:53 +0000 Received: from DM6PR12MB4202.namprd12.prod.outlook.com ([fe80::f943:600c:2558:af79]) by DM6PR12MB4202.namprd12.prod.outlook.com ([fe80::f943:600c:2558:af79%5]) with mapi id 15.20.9434.009; Sat, 20 Dec 2025 06:53:53 +0000 Message-ID: <9be1e001-2fd9-4da8-b602-4ac55002888e@amd.com> Date: Sat, 20 Dec 2025 06:53:48 +0000 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v3 1/2] Documentation/driver-api/cxl: BIOS/EFI expectation update Content-Language: en-US To: Gregory Price , 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, 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X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-OriginalArrivalTime: 20 Dec 2025 06:53:53.3730 (UTC) X-MS-Exchange-CrossTenant-FromEntityHeader: Hosted X-MS-Exchange-CrossTenant-Id: 3dd8961f-e488-4e60-8e11-a82d994e183d X-MS-Exchange-CrossTenant-MailboxType: HOSTED X-MS-Exchange-CrossTenant-UserPrincipalName: npiF75KXSS7k8jAYW+tlS9084GER3PFkPfmYLD7mD3rRFkYjjI7l5yoLREEfnhmpGLvKXzCn5iFRxECnMOfqVQ== X-MS-Exchange-Transport-CrossTenantHeadersStamped: DM4PR12MB6398 On 12/19/25 17:05, Gregory Price wrote: > 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 > --- > .../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/Documentation/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 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