PCI / ACPI: Use acpi_find_child_device() for child devices lookup

It is much more efficient to use acpi_find_child_device()
for child devices lookup in acpi_pci_find_device() and pass
ACPI_COMPANION(dev->parent) to it directly instead of obtaining
ACPI_HANDLE() of ACPI_COMPANION(dev->parent) and passing it to
acpi_find_child() which has to run acpi_bus_get_device() to
obtain ACPI_COMPANION(dev->parent) from that again.

Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Reviewed-by: Aaron Lu <aaron.lu@intel.com>

2 files changed, 13 insertions, 6 deletions

diff --git a/drivers/acpi/glue.c b/drivers/acpi/glue.c
index ea77512ad70c..9d200d5029ca 100644
--- a/drivers/acpi/glue.c
+++ b/drivers/acpi/glue.c
@@ -106,6 +106,9 @@ struct acpi_device *acpi_find_child_device(struct acpi_device *parent,
         struct acpi_device *adev, *ret = NULL;
         int ret_score = 0;
 
+        if (!parent)
+                return NULL;
+
         list_for_each_entry(adev, &parent->children, node) {
                 unsigned long long addr;
                 acpi_status status;
diff --git a/drivers/pci/pci-acpi.c b/drivers/pci/pci-acpi.c
index 43e317991326..adbf34003995 100644
--- a/drivers/pci/pci-acpi.c
+++ b/drivers/pci/pci-acpi.c
@@ -306,7 +306,8 @@ void acpi_pci_remove_bus(struct pci_bus *bus)
 static int acpi_pci_find_device(struct device *dev, acpi_handle *handle)
 {
         struct pci_dev *pci_dev = to_pci_dev(dev);
-        bool is_bridge;
+        struct acpi_device *adev;
+        bool check_children;
         u64 addr;
 
         /*
@@ -314,14 +315,17 @@ static int acpi_pci_find_device(struct device *dev, acpi_handle *handle)
          * is set only after acpi_pci_find_device() has been called for the
          * given device.
          */
-        is_bridge = pci_dev->hdr_type == PCI_HEADER_TYPE_BRIDGE
+        check_children = pci_dev->hdr_type == PCI_HEADER_TYPE_BRIDGE
                         || pci_dev->hdr_type == PCI_HEADER_TYPE_CARDBUS;
         /* Please ref to ACPI spec for the syntax of _ADR */
         addr = (PCI_SLOT(pci_dev->devfn) << 16) | PCI_FUNC(pci_dev->devfn);
-        *handle = acpi_find_child(ACPI_HANDLE(dev->parent), addr, is_bridge);
-        if (!*handle)
-                return -ENODEV;
-        return 0;
+        adev = acpi_find_child_device(ACPI_COMPANION(dev->parent), addr,
+                                      check_children);
+        if (adev) {
+                *handle = adev->handle;
+                return 0;
+        }
+        return -ENODEV;
 }
 
 static void pci_acpi_setup(struct device *dev)