Dan Williams wrote: > While it was a reasonable idea to specify no window restricitions at the > outset of the CXL emulation support, it turns out that in practice a > platform will never follow the QEMU example of specifying simultaneous > support for HDM-H and HDM-D[B] in a single window. > > HDM-D mandates extra bus cycles for host/device bias protocol, and HDM-DB > mandates extra bus cycles for back-invalidate protocol, so hardware must > be explicitly prepared for device-memory unlike host-only memory > (HDM-H). > > In preparation for the kernel dropping support for windows that do not > select between device and host-only memory, move QEMU exclusively to > declaring host-only windows.
After an offline discussion determined that a sufficiently sophisticated platform might be able to support mixed HDM-H and HDM-D[B] in the same window, so the kernel is not going to drop this support.
