[PATCH v2] xen: workaround missing device_type property in pci/pcie nodes

[Stefano Stabellini <sstabellini@xxxxxxxxxx>]

PCI buses differ from default buses in a few important ways, so it is
important to detect them properly. Normally, PCI buses are expected to
have the following property:

    device_type = "pci"

In reality, it is not always the case. To handle PCI bus nodes that
don't have the device_type property, also consider the node name: if the
node name is "pcie" or "pci" then consider the bus as a PCI bus.

This commit is based on the Linux kernel commit
d1ac0002dd29 "of: address: Work around missing device_type property in
pcie nodes".

This fixes Xen boot on RPi4. Some RPi4 kernels have the following node
on their device trees:

&pcie0 {
        pci@1,0 {
                #address-cells = <3>;
                #size-cells = <2>;
                ranges;

                reg = <0 0 0 0 0>;

                usb@1,0 {
                                reg = <0x10000 0 0 0 0>;
                                resets = <&reset 
RASPBERRYPI_FIRMWARE_RESET_ID_USB>;
                };
        };
};

The pci@1,0 node is a PCI bus. If we parse the node and its children as
a default bus, the reg property under usb@1,0 would have to be
interpreted as an address range mappable by the CPU, which is not the
case and would break.

Link: https://lore.kernel.org/xen-devel/YBmQQ3Tzu++AadKx@xxxxxxxxxxxxxxxx/
Signed-off-by: Stefano Stabellini <stefano.stabellini@xxxxxxxxxx>
---
Changes in v2:
- improve commit message

diff --git a/xen/common/device_tree.c b/xen/common/device_tree.c
index 18825e333e..f1a96a3b90 100644
--- a/xen/common/device_tree.c
+++ b/xen/common/device_tree.c
@@ -563,14 +563,28 @@ static unsigned int dt_bus_default_get_flags(const __be32 
*addr)
  * PCI bus specific translator
  */
 
+static bool_t dt_node_is_pci(const struct dt_device_node *np)
+{
+    bool is_pci = !strcmp(np->name, "pcie") || !strcmp(np->name, "pci");
+
+    if (is_pci)
+        printk(XENLOG_WARNING "%s: Missing device_type\n", np->full_name);
+
+    return is_pci;
+}
+
 static bool_t dt_bus_pci_match(const struct dt_device_node *np)
 {
     /*
      * "pciex" is PCI Express "vci" is for the /chaos bridge on 1st-gen PCI
      * powermacs "ht" is hypertransport
+     *
+     * If none of the device_type match, and that the node name is
+     * "pcie" or "pci", accept the device as PCI (with a warning).
      */
     return !strcmp(np->type, "pci") || !strcmp(np->type, "pciex") ||
-        !strcmp(np->type, "vci") || !strcmp(np->type, "ht");
+        !strcmp(np->type, "vci") || !strcmp(np->type, "ht") ||
+        dt_node_is_pci(np);
 }
 
 static void dt_bus_pci_count_cells(const struct dt_device_node *np,