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What are the plans for >> upstream today ? >> > I was discussing this with Ira and Jonathan in the LPC and CXL discord > groups. (Irq and Jonathan, please feel free to correct me) I think we > all thought that having the emulated device support in QEMU and a sample > CXL type-2 driver in the upstream kernel could be valuable for > > 1) people who wish to contribute and propose changes, like refactor, and > code tweaks related to CXL type-2 support in the kernel. They can > validate their patches to check if they break something without a CXL > type-2 device. > > 2) people who wish to contribute on solving problems of CXL type-2 > generic code, e.g. loading sequences of modules... They can get involved > without a real HW. > > My gut feeling is I can start to work with folks to get it into the > mainline together with the sample driver when CXL type-2 support is > merged. So people can play with it. I did use an emulated Type2 device for my initial development and I'm still using it for wider testing. It is basically same than the Type3 with small changes. I think a proper solution should include command line options for configuring the device with flexibility or maybe referring to a file with that specific configuration. Note there exist optional functionalities like HDM decoder, and CXL.cache will need such a flexibility as well. The RFC contains the driver for such emulated device implemented inside the tools/testing/cxl directory, although it has changed since then, but happy to share it. It is almost equal to the code inside efx_cxl.c along with the functions/macros for defining the driver. FWIW, although I'm working on Type2 support, I really think qemu could help for development and testing complex CXL infrastructures, more for memory expanders aka Type3 than Type2. I know this requires a good effort but IMO, it will pay off. > 3) people who would like to try on vfio-cxl. > > What would be nice to include in the patchset V1 in my mind: > > (Ira and Jonathan and folks please feel free to comment) > > Must have: > - HDM decoder support (>1 HDM decoder). (which I have done it in my > tree, so the CXL core can create a CXL region) > > Nice to have: > - CXLType2 device system reset handler. As what mentioned in my cover > letter, a system reset handler is required to reset the device state. > Linux kernel CXL core assumes the HW is pre-configured by FW if it sees > CXL.mem is enabled when enumerating the device. So I have to kill QEMU > instead of resetting the virtual machine when debugging. > > - CXLType2 device in the patch should be derived from PCIDevice > (current it is derived from the CXLType3 device, which carries quite > some unnecessary stuff to present to the guest) > > - Refactor of the current QEMU FWMS code to deliver the guest access > to the virtual memory backend to the correct emulated CXL device (which > is currently hardcoded to connect to cxl-type3 device in QEMU. Without > this, the access to the CXL region from the guest seems problematic but > creating CXL region is still fine.) > > Thanks, > Zhi. > >> For vfio-cxl, see : >> >> * [RFC] vfio: introduce vfio-cxl to support CXL type-2 accelerator >> passthrough >>   https://lore.kernel.org/kvm/20240920223446.1908673-1-zhiw@nvidia.com >> * [RFC] Introduce vfio-cxl to support CXL type-2 device passthrough >>   https://lore.kernel.org/all/20240921071440.1915876-1-zhiw@nvidia.com/ >> >> >> Thanks, >> >> C. >> >> >> >>> --- >>> Ira Weiny (5): >>>        hw/cxl: Use define for build bug detection >>>        hw/cxl: Refactor component register initialization >>>        hw/cxl: Derive a CXL accelerator device from Type-3 >>>        hw/cxl/accel: Add Back-Invalidate decoder capbility structure >>>        hw/cxl: Add UIO HDM decoder register fields >>> >>>   docs/system/devices/cxl.rst    | 11 ++++++ >>>   hw/cxl/cxl-component-utils.c   | 80 >>> +++++++++++++++++++----------------------- >>>   hw/mem/cxl_type3.c             | 39 ++++++++++++++++++++ >>>   include/hw/cxl/cxl_component.h | 51 +++++++++++++++++++-------- >>>   include/hw/cxl/cxl_device.h    | 16 +++++++++ >>>   include/hw/pci/pci_ids.h       |  1 + >>>   6 files changed, 141 insertions(+), 57 deletions(-) >>> --- >>> base-commit: 8eb2a03258313f404ca0c8609a8f9009b9b4318c >>> change-id: 20230517-rfc-type2-dev-c2d661a29d96 >>> >>> Best regards,