upstream: 51c48b310183ab6ba5419edfc6a8de889cc04521
pci_bridge_check_ranges() determines whether a bridge supports the optional
I/O and prefetchable memory windows and sets the flag bits in the bridge
resources. This *could* be done once during enumeration except that the
resource allocation code completely clears the flag bits, e.g., in the
pci_assign_unassigned_bridge_resources() path.
The problem with pci_bridge_check_ranges() in the resource allocation path
is that we may allocate resources after devices have been claimed by
drivers, and pci_bridge_check_ranges() *changes* the window registers to
determine whether they're writable. This may break concurrent accesses to
devices behind the bridge.
Add a new pci_read_bridge_windows() to determine whether a bridge supports
the optional windows, call it once during enumeration, remember the
results, and change pci_bridge_check_ranges() so it doesn't touch the
bridge windows but sets the flag bits based on those remembered results.
Signed-off-by: Lei Chen <lennychen@tencent.com>
Lei Chen