RE: [PATCH] hw/acpi/cxl: Drop device-memory support from CFMWS entries

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

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.