Introduce an emulated device-set plus driver to register CXL memory
devices, 'struct cxl_memdev' instances, in the mock cxl_test topology.
This enables the development of HDM Decoder (Host-managed Device Memory
Decoder) programming flow (region provisioning) in an environment that
can be updated alongside the kernel as it gains more functionality.
Whereas the cxl_pci module looks for CXL memory expanders on the 'pci'
bus, the cxl_mock_mem module attaches to CXL expanders on the platform
bus emitted by cxl_test.
Acked-by: Ben Widawsky <ben.widawsky@intel.com>
Reported-by: kernel test robot <lkp@intel.com>
Reviewed-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Link: https://lore.kernel.org/r/163116440099.2460985.10692549614409346604.stgit@dwillia2-desk3.amr.corp.intel.com
Signed-off-by: Dan Williams <dan.j.williams@intel.com>
Create an environment for CXL plumbing unit tests. Especially when it
comes to an algorithm for HDM Decoder (Host-managed Device Memory
Decoder) programming, the availability of an in-kernel-tree emulation
environment for CXL configuration complexity and corner cases speeds
development and deters regressions.
The approach taken mirrors what was done for tools/testing/nvdimm/. I.e.
an external module, cxl_test.ko built out of the tools/testing/cxl/
directory, provides mock implementations of kernel APIs and kernel
objects to simulate a real world device hierarchy.
One feedback for the tools/testing/nvdimm/ proposal was "why not do this
in QEMU?". In fact, the CXL development community has developed a QEMU
model for CXL [1]. However, there are a few blocking issues that keep
QEMU from being a tight fit for topology + provisioning unit tests:
1/ The QEMU community has yet to show interest in merging any of this
support that has had patches on the list since November 2020. So,
testing CXL to date involves building custom QEMU with out-of-tree
patches.
2/ CXL mechanisms like cross-host-bridge interleave do not have a clear
path to be emulated by QEMU without major infrastructure work. This
is easier to achieve with the alloc_mock_res() approach taken in this
patch to shortcut-define emulated system physical address ranges with
interleave behavior.
The QEMU enabling has been critical to get the driver off the ground,
and may still move forward, but it does not address the ongoing needs of
a regression testing environment and test driven development.
This patch adds an ACPI CXL Platform definition with emulated CXL
multi-ported host-bridges. A follow on patch adds emulated memory
expander devices.
Acked-by: Ben Widawsky <ben.widawsky@intel.com>
Reported-by: Vishal Verma <vishal.l.verma@intel.com>
Link: https://lore.kernel.org/r/20210202005948.241655-1-ben.widawsky@intel.com [1]
Link: https://lore.kernel.org/r/163164680798.2831381.838684634806668012.stgit@dwillia2-desk3.amr.corp.intel.com
Reviewed-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>
