xen/arm: add pci-domain for disabled devices

If a PCI host bridge device is present in the device tree, but is
disabled, then its PCI host bridge driver was not instantiated.
This results in the failure of the pci_get_host_bridge_segment()
and the following panic during Xen start:

(XEN) Device tree generation failed (-22).
(XEN)
(XEN) ****************************************
(XEN) Panic on CPU 0:
(XEN) Could not set up DOM0 guest OS
(XEN) ****************************************

Fix this by adding "linux,pci-domain" property for all device tree nodes
which have "pci" device type, so we know which segments will be used by
the guest for which bridges.

Fixes: 4cfab4425d ("xen/arm: Add linux,pci-domain property for hwdom if not available.")

Signed-off-by: Oleksandr Andrushchenko <oleksandr_andrushchenko@epam.com>
Reviewed-by: Rahul Singh <rahul.singh@arm.com>
Tested-by: Rahul Singh <rahul.singh@arm.com>
Acked-by: Julien Grall <jgrall@amazon.com>

xen/arch/arm/domain_build.c

@@ -654,6 +654,55 @@ static void __init allocate_static_memory(struct domain *d,
 }
 #endif
 
+/*
+ * When PCI passthrough is available we want to keep the
+ * "linux,pci-domain" in sync for every host bridge.
+ *
+ * Xen may not have a driver for all the host bridges. So we have
+ * to write an heuristic to detect whether a device node describes
+ * a host bridge.
+ *
+ * The current heuristic assumes that a device is a host bridge
+ * if the type is "pci" and then parent type is not "pci".
+ */
+static int handle_linux_pci_domain(struct kernel_info *kinfo,
+                                   const struct dt_device_node *node)
+{
+    uint16_t segment;
+    int res;
+
+    if ( !is_pci_passthrough_enabled() )
+        return 0;
+
+    if ( !dt_device_type_is_equal(node, "pci") )
+        return 0;
+
+    if ( node->parent && dt_device_type_is_equal(node->parent, "pci") )
+        return 0;
+
+    if ( dt_find_property(node, "linux,pci-domain", NULL) )
+        return 0;
+
+    /* Allocate and create the linux,pci-domain */
+    res = pci_get_host_bridge_segment(node, &segment);
+    if ( res < 0 )
+    {
+        res = pci_get_new_domain_nr();
+        if ( res < 0 )
+        {
+            printk(XENLOG_DEBUG "Can't assign PCI segment to %s\n",
+                   node->full_name);
+            return -FDT_ERR_NOTFOUND;
+        }
+
+        segment = res;
+        printk(XENLOG_DEBUG "Assigned segment %d to %s\n",
+               segment, node->full_name);
+    }
+
+    return fdt_property_cell(kinfo->fdt, "linux,pci-domain", segment);
+}
+
 static int __init write_properties(struct domain *d, struct kernel_info *kinfo,
                                    const struct dt_device_node *node)
 {
@@ -755,21 +804,10 @@ static int __init write_properties(struct domain *d, struct kernel_info *kinfo,
             return res;
     }
 
-    if ( is_pci_passthrough_enabled() && dt_device_type_is_equal(node, "pci") )
-    {
-        if ( !dt_find_property(node, "linux,pci-domain", NULL) )
-        {
-            uint16_t segment;
+    res = handle_linux_pci_domain(kinfo, node);
 
-            res = pci_get_host_bridge_segment(node, &segment);
-            if ( res < 0 )
-                return res;
-
-            res = fdt_property_cell(kinfo->fdt, "linux,pci-domain", segment);
-            if ( res )
-                return res;
-        }
-    }
+    if ( res )
+        return res;
 
     /*
      * Override the property "status" to disable the device when it's

xen/arch/arm/include/asm/pci.h

@@ -109,6 +109,8 @@ static always_inline bool is_pci_passthrough_enabled(void)
 
 void arch_pci_init_pdev(struct pci_dev *pdev);
 
+int pci_get_new_domain_nr(void);
+
 #else   /*!CONFIG_HAS_PCI*/
 
 struct arch_pci_dev { };
@@ -129,5 +131,11 @@ static inline int pci_get_host_bridge_segment(const struct dt_device_node *node,
     return -EINVAL;
 }
 
+static inline int pci_get_new_domain_nr(void)
+{
+    ASSERT_UNREACHABLE();
+    return -1;
+}
+
 #endif  /*!CONFIG_HAS_PCI*/
 #endif /* __ARM_PCI_H__ */

xen/arch/arm/pci/pci-host-common.c

@@ -30,6 +30,8 @@ static LIST_HEAD(pci_host_bridges);
 
 static atomic_t domain_nr = ATOMIC_INIT(-1);
 
+static int use_dt_domains = -1;
+
 static inline void __iomem *pci_remap_cfgspace(paddr_t start, size_t len)
 {
     return ioremap_nocache(start, len);
@@ -137,14 +139,16 @@ void pci_add_host_bridge(struct pci_host_bridge *bridge)
     list_add_tail(&bridge->node, &pci_host_bridges);
 }
 
-static int pci_get_new_domain_nr(void)
+int pci_get_new_domain_nr(void)
 {
+    if ( use_dt_domains )
+        return -1;
+
     return atomic_inc_return(&domain_nr);
 }
 
 static int pci_bus_find_domain_nr(struct dt_device_node *dev)
 {
-    static int use_dt_domains = -1;
     int domain;
 
     domain = dt_get_pci_domain_nr(dev);