On 02.02.2026 16:18, Roger Pau Monné wrote: > My copy of the PCI Firmware Spec v3.3 contains: > > "4.1.2. MCFG Table Description > > The MCFG table is an ACPI table that is used to communicate the base > addresses corresponding to the non-hot removable PCI Segment Groups > range within a PCI Segment Group available to the operating system at > boot. > > [...] > > 4.1.3. The _CBA Method > > Some systems may support hot plug of host bridges that introduce > either a range of buses within an existing PCI Segment Group or > introduce a new PCI Segment Group. For example, each I/O chip in a > multi-chip PCI Express root complex implementation could start a new > PCI Segment Group." > > Together with this: > > "The MCFG table format allows for more than one memory mapped base > address entry provided each entry (memory mapped configuration space > base address allocation structure) corresponds to a unique PCI Segment > Group consisting of 256 PCI buses. Multiple entries corresponding to a > single PCI Segment Group is not allowed." > > Given that each segment group can only appear once in the MCFG, and > that the _CBA method can introduce new segment groups, it would seem > to me the spec does allow for new segments appearing exclusively as > the return of _CBA method? It does read as if hot-removable segment > groups must not appear in the MCFG table. I'm not finding any clear > statement in the spec that says that ECAM areas must previously appear > in the MCFG table. > > I'm not sure how common that is, but it doesn't seem impossible given > my reading of the spec.
Hmm, that'll be a bit of work then, as Dom0 will also need to propagate the necessary data into Xen. Jan
