[PATCH v1 6/6] xen/arm: dom0less: Add a background PCI ECAM mmio region

["Edgar E. Iglesias" <edgar.iglesias@xxxxxxxxx>]

From: "Edgar E. Iglesias" <edgar.iglesias@xxxxxxx>

Add a background PCI ECAM mmio region always reading as all ones.
This indicates to the OS that there are no PCI devices on the bus.
Once the device-model's IOREQ client connects, the OS can rescan
the bus and find PV and emulated devices.

This avoids a race where domU's come up before the device models,
causing domU to crash into a data-abort when accessing ECAM.

Signed-off-by: Edgar E. Iglesias <edgar.iglesias@xxxxxxx>
---
 xen/arch/arm/dom0less-build.c | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/xen/arch/arm/dom0less-build.c b/xen/arch/arm/dom0less-build.c
index dab24fa9e2..bc5285e7fa 100644
--- a/xen/arch/arm/dom0less-build.c
+++ b/xen/arch/arm/dom0less-build.c
@@ -1015,6 +1015,16 @@ static int __init construct_domU(struct domain *d,
             kinfo.virtio_pci.mem.base = GUEST_VIRTIO_PCI_MEM_BASE;
             kinfo.virtio_pci.pf_mem.base = GUEST_VIRTIO_PCI_PREFETCH_MEM_BASE;
         }
+
+        /*
+         * Register a background PCI ECAM region returning ~0. This indicates
+         * to the OS that there are no PCI devices on the bus. Once an IOREQ
+         * client connects, the OS can rescan the bus and find devices.
+         */
+        register_mmio_bg_handler(d, true, &mmio_read_const_writes_ignored,
+                                 kinfo.virtio_pci.ecam.base,
+                                 GUEST_VIRTIO_PCI_ECAM_SIZE,
+                                 (void *) ULONG_MAX);
     }
 
     rc = dt_property_read_string(node, "xen,enhanced", &dom0less_enhanced);
-- 
2.43.0