ACPI: identify device tree root by null parent pointer, not ACPI_BUS_TYPE

We can identify the root of the ACPI device tree by the fact that it
has no parent.  This is simpler than passing around ACPI_BUS_TYPE_SYSTEM
and will help remove special treatment of the device tree root.

Currently, we add the root by hand with ACPI_BUS_TYPE_SYSTEM.  If we
traverse the tree treating the root as just another device and use
acpi_get_type(), the root shows up as ACPI_TYPE_DEVICE.

Signed-off-by: Bjorn Helgaas <bjorn.helgaas@hp.com>
Signed-off-by: Len Brown <len.brown@intel.com>

1 files changed, 13 insertions, 7 deletions

diff --git a/drivers/acpi/scan.c b/drivers/acpi/scan.c
index 27d2dec55c6..0b5aaf059c9 100644
--- a/drivers/acpi/scan.c
+++ b/drivers/acpi/scan.c
@@ -22,6 +22,8 @@ extern struct acpi_device *acpi_root;
 #define ACPI_BUS_HID                    "LNXSYBUS"
 #define ACPI_BUS_DEVICE_NAME            "System Bus"
 
+#define ACPI_IS_ROOT_DEVICE(device)    (!(device)->parent)
+
 static LIST_HEAD(acpi_device_list);
 static LIST_HEAD(acpi_bus_id_list);
 DEFINE_MUTEX(acpi_device_lock);
@@ -955,10 +957,12 @@ static void acpi_device_get_busid(struct acpi_device *device)
          * The device's Bus ID is simply the object name.
          * TBD: Shouldn't this value be unique (within the ACPI namespace)?
          */
-        switch (device->device_type) {
-        case ACPI_BUS_TYPE_SYSTEM:
+        if (ACPI_IS_ROOT_DEVICE(device)) {
                 strcpy(device->pnp.bus_id, "ACPI");
-                break;
+                return;
+        }
+
+        switch (device->device_type) {
         case ACPI_BUS_TYPE_POWER_BUTTON:
                 strcpy(device->pnp.bus_id, "PWRF");
                 break;
@@ -1093,6 +1097,11 @@ static void acpi_device_set_id(struct acpi_device *device)
 
         switch (device->device_type) {
         case ACPI_BUS_TYPE_DEVICE:
+                if (ACPI_IS_ROOT_DEVICE(device)) {
+                        hid = ACPI_SYSTEM_HID;
+                        break;
+                }
+
                 status = acpi_get_object_info(device->handle, &info);
                 if (ACPI_FAILURE(status)) {
                         printk(KERN_ERR PREFIX "%s: Error reading device info\n", __func__);
@@ -1129,9 +1138,6 @@ static void acpi_device_set_id(struct acpi_device *device)
         case ACPI_BUS_TYPE_PROCESSOR:
                 hid = ACPI_PROCESSOR_OBJECT_HID;
                 break;
-        case ACPI_BUS_TYPE_SYSTEM:
-                hid = ACPI_SYSTEM_HID;
-                break;
         case ACPI_BUS_TYPE_THERMAL:
                 hid = ACPI_THERMAL_HID;
                 break;
@@ -1643,7 +1649,7 @@ int __init acpi_scan_init(void)
          * Create the root device in the bus's device tree
          */
         result = acpi_add_single_object(&acpi_root, ACPI_ROOT_OBJECT,
-                                        ACPI_BUS_TYPE_SYSTEM, &ops);
+                                        ACPI_BUS_TYPE_DEVICE, &ops);
         if (result)
                 goto Done;