A hypervisor may want to perform PCI resource allocation
(bus numbers, io and mmio ranges) and program the
resulting values into the devices itself rather than
delegate this to the firmware.

One possible reason for doing so is more control for the
hypervisor over assigned ranges. This will also be faster
than entering the guest and then trapping on config
space accesses.

Introduce a new flag in fw_cfg, "etc/pci-noalloc", to
instruct the firmware to skip the resource allocation
phase and use whatever is already programmed in the
devices.

Signed-off-by: Abhimanyu Saini <sainiabr@amazon.de>
---
 src/fw/pciinit.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/src/fw/pciinit.c b/src/fw/pciinit.c
index 334fd30c..e1c05410 100644
--- a/src/fw/pciinit.c
+++ b/src/fw/pciinit.c
@@ -1176,8 +1176,13 @@ static void pci_bios_map_devices(struct pci_bus *busses)
 
 static void pci_allocate_resources(void)
 {
+    u64 noalloc;
     struct pci_bus *busses;
 
+    noalloc = romfile_loadint("etc/pci-noalloc", 0);
+    if (noalloc)
+        return;
+
     dprintf(1, "=== PCI new allocation pass #1 ===\n");
     busses = malloc_tmp(sizeof(*busses) * (MaxPCIBus + 1));
     if (!busses) {
-- 
2.40.1




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