Re: [PATCH 00/23] cxl_test: Enable CXL Topology and UAPI regression tests

[Dan Williams <dan.j.williams@intel.com>]

On Tue, Aug 10, 2021 at 3:10 PM Ben Widawsky <ben.widawsky@intel.com> wrote:
>
> On 21-08-09 15:27:47, Dan Williams wrote:
> > As mentioned in patch 20 in this series the response of upstream QEMU
> > community to CXL device emulation has been underwhelming to date. Even
> > if that picked up it still results in a situation where new driver
> > features and new test capabilities for those features are split across
> > multiple repositories.
> >
> > The "nfit_test" approach of mocking up platform resources via an
> > external test module continues to yield positive results catching
> > regressions early and often. Repeat that success with a "cxl_test"
> > module to inject custom crafted topologies and command responses into
> > the CXL subsystem's sysfs and ioctl UAPIs.
> >
> > The first target for cxl_test to verify is the integration of CXL with
> > LIBNVDIMM and the new support for the CXL namespace label + region-label
> > format. The first 11 patches introduce support for the new label format.
> >
> > The next 9 patches rework the CXL PCI driver and to move more common
> > infrastructure into the core for the unit test environment to reuse. The
> > largest change here is disconnecting the mailbox command processing
> > infrastructure from the PCI specific transport. The unit test
> > environment replaces the PCI transport with a custom backend with mocked
> > responses to command requests.
> >
> > Patch 20 introduces just enough mocked functionality for the cxl_acpi
> > driver to load against cxl_test resources. Patch 21 fixes the first bug
> > discovered by this framework, namely that HDM decoder target list maps
> > were not being filled out.
> >
> > Finally patches 22 and 23 introduce a cxl_test representation of memory
> > expander devices. In this initial implementation these memory expander
> > targets implement just enough command support to pass the basic driver
> > init sequence and enable label command passthrough to LIBNVDIMM.
> >
> > The topology of cxl_test includes:
> > - (4) platform fixed memory windows. One each of a x1-volatile,
> >   x4-volatile, x1-persistent, and x4-persistent.
> > - (4) Host bridges each with (2) root ports
> > - (8) CXL memory expanders, one for each root port
> > - Each memory expander device supports the GET_SUPPORTED_LOGS, GET_LOG,
> >   IDENTIFY, GET_LSA, and SET_LSA commands.
> >
> > Going forward the expectation is that where possible new UAPI visible
> > subsystem functionality comes with cxl_test emulation of the same.
> >
> > The build process for cxl_test is:
> >
> >     make M=tools/testing/cxl
> >     make M=tools/testing/cxl modules_install
> >
> > The implementation methodology of the test module is the same as
> > nfit_test where the bulk of the emulation comes from replacing symbols
> > that cxl_acpi and the cxl_core import with mocked implementation of
> > those symbols. See the "--wrap=" lines in tools/testing/cxl/Kbuild. Some
> > symbols need to be replaced, but are local to the modules like
> > match_add_root_ports(). In those cases the local symbol is marked __weak
> > with a strong implementation coming from tools/testing/cxl/. The goal
> > being to be minimally invasive to production code paths.
>
> I went through everything except the very last patch, which I'll try to get to
> tomorrow when my brain is working a bit better. It looks fine to me overall. I'd
> like if we could remove code duplication in the mock driver, but perhaps that's
> the nature of the beast here.

Well, maybe not. I.e. I don't think it would be out of the question to
wrap this common sequence into a helper that both cxl_pci and
cxl_mock_mem share:

        rc = cxl_mem_enumerate_cmds(cxlm);
        if (rc)
                return rc;

        rc = cxl_mem_identify(cxlm);
        if (rc)
                return rc;

        rc = cxl_mem_create_range_info(cxlm);
        if (rc)
                return rc;

        cxlmd = devm_cxl_add_memdev(dev, cxlm);
        if (IS_ERR(cxlmd))
                return PTR_ERR(cxlmd);

        if (range_len(&cxlm->pmem_range) && IS_ENABLED(CONFIG_CXL_PMEM))
                rc = devm_cxl_add_nvdimm(dev, cxlmd);

...or are you thinking of a different place where there's duplication?