On 5/12/25 9:21 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@xxxxxxxxxx> Reviewed-by: Dave Jiang <dave.jiang@xxxxxxxxx> > --- > 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/index.rst b/Documentation/driver-api/cxl/index.rst > index 6a5fb7e00c52..bc2228c77c32 100644 > --- a/Documentation/driver-api/cxl/index.rst > +++ b/Documentation/driver-api/cxl/index.rst > @@ -30,9 +30,10 @@ that have impacts on each other. The docs here break up configurations steps. > platform/example-configs > > .. toctree:: > - :maxdepth: 1 > + :maxdepth: 2 > :caption: Linux Kernel Configuration > > + linux/overview > linux/access-coordinates > > > diff --git a/Documentation/driver-api/cxl/linux/overview.rst b/Documentation/driver-api/cxl/linux/overview.rst > new file mode 100644 > index 000000000000..648beb2c8c83 > --- /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 device is CXL, marking it for probe by CXL driver > + > +3) CXL Driver Operation > + > + a) Base device creation > + > + * root, port, and memdev devices created > + * CEDT CFMWS IO Resource creation > + > + b) Decoder creation > + > + * root, switch, and endpoint decoders created > + > + c) Logical device creation > + > + * memory_region and endpoint devices created > + > + d) Devices are associated with each other > + > + * If auto-decoder (BIOS-programmed decoders), driver validates > + configurations, builds associations, and locks configs at probe time. > + > + * If user-configured, validation and associations are built at > + decoder-commit time. > + > + e) Regions surfaced as DAX region > + > + * dax_region created > + > + * DAX device created via DAX driver > + > +4) DAX Driver Operation > + > + a) DAX driver surfaces DAX region as one of two dax device modes > + > + * kmem - dax device is converted to hotplug memory blocks > + > + * DAX kmem IO Resource creation > + > + * hmem - dax device is left as daxdev to be accessed as a file. > + > + * If hmem, journey ends here. > + > + b) DAX kmem surfaces memory region to Memory Hotplug to add to page > + allocator as "driver managed memory" > + > +5) Memory Hotplug > + > + a) mhp component surfaces a dax device memory region as multiple memory > + blocks to the page allocator > + > + * blocks appear in :code:`/sys/bus/memory/devices` and linked to a NUMA node > + > + b) blocks are onlined into the requested zone (NORMAL or MOVABLE) > + > + * Memory is marked "Driver Managed" to avoid kexec from using it as region > + for kernel updates
