Re: [PATCH v5 1/9] cxl/mem: Introduce a driver for CXL-2.0-Type-3 endpoints

From: Dan Williams <dan.j.williams(a)intel.com&gt; 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. Link: https://www.computeexpresslink.org/download-the-specification Cc: Jonathan Corbet <corbet(a)lwn.net&gt; Signed-off-by: Dan Williams <dan.j.williams(a)intel.com&gt; Signed-off-by: Ben Widawsky <ben.widawsky(a)intel.com&gt; Acked-by: David Rientjes <rientjes(a)google.com&gt; (v1)