Hi Oleksandr, > On 9 Dec 2021, at 7:29 am, Oleksandr Andrushchenko <[email protected]> wrote: > > From: Oleksandr Andrushchenko <[email protected]> > > PCI host bridges are special devices in terms of implementing PCI > passthrough. According to [1] the current implementation depends on > Domain-0 to perform the initialization of the relevant PCI host > bridge hardware and perform PCI device enumeration. In order to > achieve that one of the required changes is to not map all the memory > ranges in map_range_to_domain as we traverse the device tree on startup > and perform some additional checks if the range needs to be mapped to > Domain-0. > > The generic PCI host controller device tree binding says [2]: > - ranges: As described in IEEE Std 1275-1994, but must provide > at least a definition of non-prefetchable memory. One > or both of prefetchable Memory and IO Space may also > be provided. > > - reg : The Configuration Space base address and size, as accessed > from the parent bus. The base address corresponds to > the first bus in the "bus-range" property. If no > "bus-range" is specified, this will be bus 0 (the default). > > From the above none of the memory ranges from the "ranges" property > needs to be mapped to Domain-0 at startup as MMIO mapping is going to > be handled dynamically by vPCI as we assign PCI devices, e.g. each > device assigned to Domain-0/guest will have its MMIOs mapped/unmapped > as needed by Xen. > > The "reg" property covers not only ECAM space, but may also have other > then the configuration memory ranges described, for example [3]: > - reg: Should contain rc_dbi, config registers location and length. > - reg-names: Must include the following entries: > "rc_dbi": controller configuration registers; > "config": PCIe configuration space registers. > > This patch makes it possible to not map all the ranges from the > "ranges" property and also ECAM from the "reg". All the rest from the > "reg" property still needs to be mapped to Domain-0, so the PCI > host bridge remains functional in Domain-0. This is done by first > skipping the mappings while traversing the device tree as it is done for > usual devices and then by calling a dedicated pci_host_bridge_mappings > function which only maps MMIOs required by the host bridges leaving the > regions, needed for vPCI traps, unmapped. > > [1] https://lists.xenproject.org/archives/html/xen-devel/2020-07/msg00777.html > [2] > https://www.kernel.org/doc/Documentation/devicetree/bindings/pci/host-generic-pci.txt > [3] > https://www.kernel.org/doc/Documentation/devicetree/bindings/pci/hisilicon-pcie.txt > > Signed-off-by: Oleksandr Andrushchenko <[email protected]> > Reviewed-by: Julien Grall <[email protected]>
Reviewed-by: Rahul Singh <[email protected]> Tested-by: Rahul Singh <[email protected]> Regards, Rahul
