ACPI / hotplug / PCI: Make device_is_managed_by_native_pciehp() public

We're about to add runtime PM of hotplug ports, but we need to restrict it
to ports that are handled natively by the OS: If they're handled by the
firmware (which is the case for Thunderbolt on non-Macs), things would
break if the OS put the ports into D3hot behind the firmware's back.

To determine if a hotplug port is handled natively, one has to walk up from
the port to the root bridge and check the cached _OSC Control Field for the
value of the "PCI Express Native Hot Plug control" bit. There's already a
function to do that, device_is_managed_by_native_pciehp(), but it's private
to drivers/pci/hotplug/acpiphp_glue.c and only compiled in if
CONFIG_HOTPLUG_PCI_ACPI is enabled.

Make it public and move it to drivers/pci/pci-acpi.c, so that it is
available in the more general CONFIG_ACPI case.

The function contains a check if the device in question is a hotplug port
and returns false if it's not. The caller we're going to add doesn't need
this as it only calls the function if it actually *is* a hotplug port.
Move the check out of the function into the single existing caller.

Rename it to pciehp_is_native() and add some kerneldoc and polish.

No functional change intended.

Tested-by: Mika Westerberg <[e-mail]>
Signed-off-by: Lukas Wunner <[e-mail]>
Signed-off-by: Bjorn Helgaas <[e-mail]>
Reviewed-by: Rafael J. Wysocki <[e-mail]>

drivers/pci/hotplug/acpiphp_glue.c

···
 	acpiphp_let_context_go(context);
 }
 
-/* Check whether the PCI device is managed by native PCIe hotplug driver */
-static bool device_is_managed_by_native_pciehp(struct pci_dev *pdev)
-{
-	acpi_handle tmp;
-	struct acpi_pci_root *root;
-
-	/* Check whether the PCIe port supports native PCIe hotplug */
-	if (!pdev->is_hotplug_bridge)
-		return false;
-
-	/*
-	 * Check whether native PCIe hotplug has been enabled for
-	 * this PCIe hierarchy.
-	 */
-	tmp = acpi_find_root_bridge_handle(pdev);
-	if (!tmp)
-		return false;
-	root = acpi_pci_find_root(tmp);
-	if (!root)
-		return false;
-	if (!(root->osc_control_set & OSC_PCI_EXPRESS_NATIVE_HP_CONTROL))
-		return false;
-
-	return true;
-}
-
 /**
  * acpiphp_add_context - Add ACPIPHP context to an ACPI device object.
  * @handle: ACPI handle of the object to add a context to.
···
 	 * expose slots to user space in those cases.
 	 */
 	if ((acpi_pci_check_ejectable(pbus, handle) || is_dock_device(adev))
-	    && !(pdev && device_is_managed_by_native_pciehp(pdev))) {
+	    && !(pdev && pdev->is_hotplug_bridge && pciehp_is_native(pdev))) {
 		unsigned long long sun;
 		int retval;
 

drivers/pci/pci-acpi.c

···
 EXPORT_SYMBOL_GPL(pci_get_hp_params);
 
 /**
+ * pciehp_is_native - Check whether a hotplug port is handled by the OS
+ * @pdev: Hotplug port to check
+ *
+ * Walk up from @pdev to the host bridge, obtain its cached _OSC Control Field
+ * and return the value of the "PCI Express Native Hot Plug control" bit.
+ * On failure to obtain the _OSC Control Field return %false.
+ */
+bool pciehp_is_native(struct pci_dev *pdev)
+{
+	struct acpi_pci_root *root;
+	acpi_handle handle;
+
+	handle = acpi_find_root_bridge_handle(pdev);
+	if (!handle)
+		return false;
+
+	root = acpi_pci_find_root(handle);
+	if (!root)
+		return false;
+
+	return root->osc_control_set & OSC_PCI_EXPRESS_NATIVE_HP_CONTROL;
+}
+
+/**
  * pci_acpi_wake_bus - Root bus wakeup notification fork function.
  * @work: Work item to handle.
  */

include/linux/pci_hotplug.h

···
 #ifdef CONFIG_ACPI
 #include <linux/acpi.h>
 int pci_get_hp_params(struct pci_dev *dev, struct hotplug_params *hpp);
+bool pciehp_is_native(struct pci_dev *pdev);
 int acpi_get_hp_hw_control_from_firmware(struct pci_dev *dev, u32 flags);
 int acpi_pci_check_ejectable(struct pci_bus *pbus, acpi_handle handle);
 int acpi_pci_detect_ejectable(acpi_handle handle);
···
 {
 	return -ENODEV;
 }
+static inline bool pciehp_is_native(struct pci_dev *pdev) { return true; }
 #endif
 #endif