linux-kernel - Re: [RFC PATCH v2 06/18] cxl: docs/linux

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Message-ID: <6d2a2e4a-743c-42bf-b45f-c136b07f47c1@infradead.org>
Date: Sat, 10 May 2025 19:06:04 -0700
From: Randy Dunlap <rdunlap@...radead.org>
To: Gregory Price <gourry@...rry.net>, linux-cxl@...r.kernel.org
Cc: linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
 kernel-team@...a.com, dave@...olabs.net, jonathan.cameron@...wei.com,
 dave.jiang@...el.com, alison.schofield@...el.com, vishal.l.verma@...el.com,
 ira.weiny@...el.com, dan.j.williams@...el.com, corbet@....net
Subject: Re: [RFC PATCH v2 06/18] cxl: docs/linux - overview



On 4/30/25 11:10 AM, Gregory Price wrote:
> Add type-3 device configuration overview that explains the probe
> process for a type-3 device from early-boot through memory-hotplug.
> 
> Signed-off-by: Gregory Price <gourry@...rry.net>
> ---
>  Documentation/driver-api/cxl/index.rst        |   3 +-
>  .../driver-api/cxl/linux/overview.rst         | 103 ++++++++++++++++++
>  2 files changed, 105 insertions(+), 1 deletion(-)
>  create mode 100644 Documentation/driver-api/cxl/linux/overview.rst
> 


>  
> diff --git a/Documentation/driver-api/cxl/linux/overview.rst b/Documentation/driver-api/cxl/linux/overview.rst
> new file mode 100644
> index 000000000000..f440d79d77d1
> --- /dev/null
> +++ b/Documentation/driver-api/cxl/linux/overview.rst
> @@ -0,0 +1,103 @@
> +.. SPDX-License-Identifier: GPL-2.0
> +
> +========
> +Overview
> +========
> +
> +This section presents the configuration process of a CXL Type-3 memory device,
> +and how it is ultimately exposed to users as either a :code:`DAX` device or
> +normal memory pages via the kernel's page allocator.
> +
> +Portions marked with a bullet are points at which certain kernel objects
> +are generated.
> +
> +1) Early Boot
> +
> +  a) BIOS, Build, and Boot Parameters
> +
> +    i) EFI_MEMORY_SP
> +    ii) CONFIG_EFI_SOFT_RESERVE
> +    iii) CONFIG_MHP_DEFAULT_ONLINE_TYPE
> +    iv) nosoftreserve
> +
> +  b) Memory Map Creation
> +
> +    i) EFI Memory Map / E820 Consulted for Soft-Reserved
> +
> +      * CXL Memory is set aside to be handled by the CXL driver
> +
> +      * Soft-Reserved IO Resource created for CFMWS entry
> +
> +  c) NUMA Node Creation
> +
> +    * Nodes created from ACPI CEDT CFMWS and SRAT Proximity domains (PXM)
> +
> +  d) Memory Tier Creation
> +
> +    * A default memory_tier is created with all nodes.
> +
> +  e) Contiguous Memory Allocation
> +
> +    * Any requested CMA is allocated from Online nodes
> +
> +  f) Init Finishes, Drivers start probing
> +
> +2) ACPI and PCI Drivers
> +
> +  a) Detects PCI devices is CXL, marking it for probe by CXL driver

                    device

> +
> +3) CXL Driver Operation


-- 
~Randy