linux/tools/testing/cxl/Kbuild
Dan Williams 67dcdd4d3b tools/testing/cxl: Introduce a mocked-up CXL port hierarchy
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>
2021-09-21 13:47:10 -07:00

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Makefile

# SPDX-License-Identifier: GPL-2.0
ldflags-y += --wrap=is_acpi_device_node
ldflags-y += --wrap=acpi_get_table
ldflags-y += --wrap=acpi_put_table
ldflags-y += --wrap=acpi_evaluate_integer
ldflags-y += --wrap=acpi_pci_find_root
ldflags-y += --wrap=pci_walk_bus
ldflags-y += --wrap=nvdimm_bus_register
DRIVERS := ../../../drivers
CXL_SRC := $(DRIVERS)/cxl
CXL_CORE_SRC := $(DRIVERS)/cxl/core
ccflags-y := -I$(srctree)/drivers/cxl/
ccflags-y += -D__mock=__weak
obj-m += cxl_acpi.o
cxl_acpi-y := $(CXL_SRC)/acpi.o
cxl_acpi-y += mock_acpi.o
cxl_acpi-y += config_check.o
obj-m += cxl_pmem.o
cxl_pmem-y := $(CXL_SRC)/pmem.o
cxl_pmem-y += config_check.o
obj-m += cxl_core.o
cxl_core-y := $(CXL_CORE_SRC)/bus.o
cxl_core-y += $(CXL_CORE_SRC)/pmem.o
cxl_core-y += $(CXL_CORE_SRC)/regs.o
cxl_core-y += $(CXL_CORE_SRC)/memdev.o
cxl_core-y += $(CXL_CORE_SRC)/mbox.o
cxl_core-y += config_check.o
obj-m += test/