[PATCH v4 0/6] hw/riscv/virt: Add CXL support to the RISC-V virt machine

[Chen Pei <cp0613@linux.alibaba.com>]

This series adds CXL support to the RISC-V virt machine, following the
approach used by the ARM virt machine: CXL host bridges (pxb-cxl) are
described as ACPI0016 devices, an ACPI0017 (CXLM) device is added to the
DSDT with a _DEP on the CXL host bridges, and a CEDT table is built. A
bios-tables test is added to pin down the generated ACPI tables.

Changes since v3
----------------
  - The CXL host bridge resource handling is reworked, following Junjie
    Cao's suggestion (and Igor Mammedov's earlier "fix UEFI" direction):
    instead of reserving a fixed 256 MiB carve-out and simulating the
    firmware PCI initialization in QEMU, the machine now advertises the
    pxb-cxl expander root buses to firmware via the etc/extra-pci-roots
    fw_cfg file (pci_bus_add_fw_cfg_extra_pci_roots(), as arm/virt and
    x86 do).  EDK2's PciBusDxe then enumerates behind the CXL host
    bridge and assigns the root-port window and bus numbers, and
    build_crs() emits a correct _CRS for the ACPI0016 host bridge.
    This keeps the machine code minimal (a single call, no carve-out),
    scales to multiple pxb-cxl host bridges, and lets firmware size the
    window to what is actually behind the bridge.
  - The bios-tables test is split into the staged flow documented in
    bios-tables-test.c, and ordered the same way the riscv64 goldens were
    originally added upstream (Sunil V L's commit cc3ba2422554 et al.):
    the feature code comes first, then three consecutive commits -- empty
    golden files + allowed-diff.h, the test code, and the populated golden
    master binaries with an emptied allowed-diff.h.

Changes since v2
----------------
  - hw/riscv/virt: The MMIO-window patch no longer touches the common
    gpex code (Igor).  The gpex_cfg.cxl_mmio32 field and the is_cxl
    static _CRS branch are dropped; the ACPI0016 _CRS now comes from the
    generic build_crs() path.  Since EDK2 does not enumerate the pxb-cxl
    expander bridge, riscv simulates the firmware PCI initialization
    (reserved window + depth-first bridge bus numbers) and re-applies it
    via a reset handler.
  - hw/riscv/virt: Drops the machine-global window/bus-range synthesis
    that did not scale past one pxb-cxl (Junjie).  The series targets a
    single CXL host bridge for now, documented in the commit message and
    a TODO.
  - hw/riscv/virt: CXL host register region and FMW setup folded into a
    single cxl_host_state_init() helper; redundant braces removed in
    create_fdt_pcie() (Daniel).
  - hw/riscv/virt-acpi-build: the _DEP commit message documents the
    kernel-compatibility behaviour (Alistair).
  - Carried review tags: Sunil V L's Reviewed-by on the _DEP patch and
    Alistair Francis's Acked-by on the test.

Changes since v1
----------------
  - hw/riscv/virt: PCIBus *bus renamed to PCIBus *pci_bus (Jonathan).
  - hw/riscv/virt: Dropped outer if (s->pci_bus) guard around
    cxl_hook_up_pxb_registers(); the function already handles a NULL
    bus internally (Jonathan).
  - hw/riscv/virt-acpi-build: All s->bus references updated to
    s->pci_bus; iasl -d decompiled DSDT fragment added to commit
    message.
  - hw/riscv/virt,gpex: Commit message expanded with PCI-to-PCI Bridge
    Spec §3.2.5.8/9/10 citations (Jonathan).
  - Original patch 4 ("Map committed HDM decoder ranges as RAM for
    direct DMA") dropped; superseded by Alireza Sanaee's v8 series [1],
    which is now merged upstream and thus no longer a prerequisite.
  - New patch 4: RISC-V ACPI bios-tables test for CXL, with golden AML
    files generated and included.

[1] https://lore.kernel.org/qemu-devel/20260318171918.146-1-alireza.sanaee@huawei.com/

Test
----
Built riscv64-softmmu and ran the new bios-tables test together with the
existing riscv64 ACPI tests; all pass.

Also booted an RVA22 guest with EDK2 firmware, using pxb-cxl + cxl-rp +
cxl-type3 + a CFMW: EDK2's PciBusDxe enumerates behind the CXL host
bridge (advertised via etc/extra-pci-roots), the root port and Type3
device show up (0000:0c:00.0 / 0000:0d:00.0), and 'cxl list' reports
the memdev (4 GiB) and the CFMWS root decoder.

QEMU invocation (CXL-relevant options shown):

    qemu-system-riscv64 \
        -M virt,aia=aplic-imsic,acpi=on,cxl=on \
        -cpu rva22s64 -smp 2 -m 4G \
        -object memory-backend-ram,id=vmem0,share=on,size=4G \
        -device pxb-cxl,bus_nr=12,bus=pcie.0,id=cxl.1 \
        -device cxl-rp,port=0,bus=cxl.1,id=rp0,chassis=0,slot=2 \
        -device cxl-type3,bus=rp0,volatile-memdev=vmem0 \
        -M cxl-fmw.0.targets.0=cxl.1,cxl-fmw.0.size=4G \
        ...

Verification (total system memory grows by 4 GiB after onlining):

    # cxl list
    # cxl enable-memdev mem0
    # cxl create-region -m -t ram -d decoder0.0 -w 1 mem0 -s 4G
    # daxctl online-memory dax0.0
    # free -h

Chen Pei (6):
  hw/riscv/virt: Add CXL support to the RISC-V virt machine
  hw/riscv/virt-acpi-build: Add _DEP to ACPI0017 for CXL host bridge
    dependency
  hw/riscv/virt: Advertise the CXL host bridge to firmware via
    extra-pci-roots
  tests/qtest: Prepare golden files for the RISC-V CXL ACPI test
  tests/qtest: Add RISC-V ACPI bios tables test for CXL
  tests/qtest: Update RISC-V CXL ACPI golden master binaries

 hw/riscv/Kconfig                      |   2 +
 hw/riscv/virt-acpi-build.c            |  52 +++++++++++++++++++++++++
 hw/riscv/virt.c                       |  45 +++++++++++++++++++++
 include/hw/riscv/virt.h               |   3 ++
 tests/data/acpi/riscv64/virt/CEDT.cxl | Bin 0 -> 108 bytes
 tests/data/acpi/riscv64/virt/DSDT.cxl | Bin 0 -> 6331 bytes
 tests/qtest/bios-tables-test.c        |  54 ++++++++++++++++++++++++++
 7 files changed, 156 insertions(+)
 create mode 100644 tests/data/acpi/riscv64/virt/CEDT.cxl
 create mode 100644 tests/data/acpi/riscv64/virt/DSDT.cxl

-- 
2.50.1