Provide a survey of the work-in-progress maturity (implementation
status) of various aspects of the CXL subsystem.
Clarify that in addition to ongoing upkeep relative to specification
updates, there are some long running themes in the driver that respond
to the discovery of new corner cases (bugs) and new use cases (feature
extensions).
The primary audience is distribution maintainers, but it also serves as
a guide for kernel developers to understand what aspects of the CXL
subsystem need more help. It is a landing page to document ongoing
progress, and a guide to discern exposure to work-in-progress features.
Reviewed-by: Adam Manzanares <a.manzanares@samsung.com>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>
Reviewed-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Reviewed-by: Ira Weiny <ira.weiny@intel.com>
Reviewed-by: Alison Schofield <alison.schofield@intel.com>
Link: https://patch.msgid.link/172005486862.2048248.6668794717827294862.stgit@dwillia2-xfh.jf.intel.com
Signed-off-by: Dave Jiang <dave.jiang@intel.com>
The CXL.mem protocol allows a device to act as a provider of "System
RAM" and/or "Persistent Memory" that is fully coherent as if the memory
was attached to the typical CPU memory controller.
With the CXL-2.0 specification a PCI endpoint can implement a "Type-3"
device interface and give the operating system control over "Host
Managed Device Memory". See section 2.3 Type 3 CXL Device.
The memory range exported by the device may optionally be described by
the platform firmware memory map, or by infrastructure like LIBNVDIMM to
provision persistent memory capacity from one, or more, CXL.mem devices.
A pre-requisite for Linux-managed memory-capacity provisioning is this
cxl_mem driver that can speak the mailbox protocol defined in section
8.2.8.4 Mailbox Registers.
For now just land the initial driver boiler-plate and Documentation/
infrastructure.
Signed-off-by: Ben Widawsky <ben.widawsky@intel.com>
Reviewed-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Acked-by: David Rientjes <rientjes@google.com> (v1)
Cc: Jonathan Corbet <corbet@lwn.net>
Link: https://www.computeexpresslink.org/download-the-specification
Link: https://lore.kernel.org/r/20210217040958.1354670-2-ben.widawsky@intel.com
Signed-off-by: Dan Williams <dan.j.williams@intel.com>
