Subject: [PATCH] ACPI, PCI: Revert reverting of "PCI/ACPI: Request _OSC control before scanning PCI root bus"

In
| commit b8178f130e25c1bdac1c33e0996f1ff6e20ec08e
| Author: Bjorn Helgaas <bhelgaas@google.com>
| Date:   Mon Apr 1 15:47:39 2013 -0600
|
|    Revert "PCI/ACPI: Request _OSC control before scanning PCI root bus"
|
|    This reverts commit 8c33f51df406e1a1f7fa4e9b244845b7ebd61fa6.
for v3.9, "OSC set early" is reverted.

Now we have problem on v3.10, as it has
       - Remove ACPI PCI subdrivers (Jiang Liu, Myron Stowe)
       - Make acpiphp builtin only, not modular (Jiang Liu)
   acpiphp get registered with pcibios_add_bus very early.
We can not enable pcie native hotplug driver any more if system support
acpiphp and pciehp.

Calling path: in acpi_pci_root_add we have
1. pci_acpi_scan_root
     ==> pci devices enumeration and bus scanning.
       ==> pci_alloc_child_bus
         ==> pcibios_add_bus
           ==> acpi_pci_add_bus
             ==> acpiphp_enumerate_slots
               ==> ...==> register_slot
                 ==> device_is_managed_by_native_pciehp
                   ==> check osc_set with OSC_PCI_EXPRESS_NATIVE_HP_CONTROL
2. _OSC set request
so we always have acpiphp hotplug slot registered at first, as OSC is
not set yet.

We need "OSC set early" before pci_apci_scan_root again.

The point: later aspm, pme, pciehp, aer support would rely on value in
root osc_support_set/osc_control_set.

For v3.10, let's put the "osc control set early" back,
as we have user in pci_acpi_scan_root.

Signed-off-by: Yinghai Lu <yinghai@kernel.org>

diff --git a/drivers/acpi/pci_root.c b/drivers/acpi/pci_root.c
index e427dc5..207d773 100644
--- a/drivers/acpi/pci_root.c
+++ b/drivers/acpi/pci_root.c
@@ -382,6 +382,7 @@ static int acpi_pci_root_add(struct acpi_device *device,
 	int result;
 	struct acpi_pci_root *root;
 	u32 flags, base_flags;
+	bool is_osc_granted = false;
 
 	root = kzalloc(sizeof(struct acpi_pci_root), GFP_KERNEL);
 	if (!root)
@@ -442,30 +443,6 @@ static int acpi_pci_root_add(struct acpi_device *device,
 	flags = base_flags = OSC_PCI_SEGMENT_GROUPS_SUPPORT;
 	acpi_pci_osc_support(root, flags);
 
-	/*
-	 * TBD: Need PCI interface for enumeration/configuration of roots.
-	 */
-
-	mutex_lock(&acpi_pci_root_lock);
-	list_add_tail(&root->node, &acpi_pci_roots);
-	mutex_unlock(&acpi_pci_root_lock);
-
-	/*
-	 * Scan the Root Bridge
-	 * --------------------
-	 * Must do this prior to any attempt to bind the root device, as the
-	 * PCI namespace does not get created until this call is made (and
-	 * thus the root bridge's pci_dev does not exist).
-	 */
-	root->bus = pci_acpi_scan_root(root);
-	if (!root->bus) {
-		printk(KERN_ERR PREFIX
-			    "Bus %04x:%02x not present in PCI namespace\n",
-			    root->segment, (unsigned int)root->secondary.start);
-		result = -ENODEV;
-		goto out_del_root;
-	}
-
 	/* Indicate support for various _OSC capabilities. */
 	if (pci_ext_cfg_avail())
 		flags |= OSC_EXT_PCI_CONFIG_SUPPORT;
@@ -484,7 +461,6 @@ static int acpi_pci_root_add(struct acpi_device *device,
 			flags = base_flags;
 		}
 	}
-
 	if (!pcie_ports_disabled
 	    && (flags & ACPI_PCIE_REQ_SUPPORT) == ACPI_PCIE_REQ_SUPPORT) {
 		flags = OSC_PCI_EXPRESS_CAP_STRUCTURE_CONTROL
@@ -505,28 +481,54 @@ static int acpi_pci_root_add(struct acpi_device *device,
 		status = acpi_pci_osc_control_set(device->handle, &flags,
 				       OSC_PCI_EXPRESS_CAP_STRUCTURE_CONTROL);
 		if (ACPI_SUCCESS(status)) {
+			is_osc_granted = true;
 			dev_info(&device->dev,
 				"ACPI _OSC control (0x%02x) granted\n", flags);
-			if (acpi_gbl_FADT.boot_flags & ACPI_FADT_NO_ASPM) {
-				/*
-				 * We have ASPM control, but the FADT indicates
-				 * that it's unsupported. Clear it.
-				 */
-				pcie_clear_aspm(root->bus);
-			}
 		} else {
+			is_osc_granted = false;
 			dev_info(&device->dev,
 				"ACPI _OSC request failed (%s), "
 				"returned control mask: 0x%02x\n",
 				acpi_format_exception(status), flags);
-			pr_info("ACPI _OSC control for PCIe not granted, "
-				"disabling ASPM\n");
-			pcie_no_aspm();
 		}
 	} else {
 		dev_info(&device->dev,
-			 "Unable to request _OSC control "
-			 "(_OSC support mask: 0x%02x)\n", flags);
+			"Unable to request _OSC control "
+			"(_OSC support mask: 0x%02x)\n", flags);
+	}
+
+	/*
+	 * TBD: Need PCI interface for enumeration/configuration of roots.
+	 */
+
+	mutex_lock(&acpi_pci_root_lock);
+	list_add_tail(&root->node, &acpi_pci_roots);
+	mutex_unlock(&acpi_pci_root_lock);
+
+	/*
+	 * Scan the Root Bridge
+	 * --------------------
+	 * Must do this prior to any attempt to bind the root device, as the
+	 * PCI namespace does not get created until this call is made (and 
+	 * thus the root bridge's pci_dev does not exist).
+	 */
+	root->bus = pci_acpi_scan_root(root);
+	if (!root->bus) {
+		printk(KERN_ERR PREFIX
+			    "Bus %04x:%02x not present in PCI namespace\n",
+			    root->segment, (unsigned int)root->secondary.start);
+		result = -ENODEV;
+		goto out_del_root;
+	}
+
+	/* ASPM setting */
+	if (is_osc_granted) {
+		if (acpi_gbl_FADT.boot_flags & ACPI_FADT_NO_ASPM)
+			pcie_clear_aspm(root->bus);
+	} else {
+		pr_info("ACPI _OSC control for PCIe not granted, "
+			"disabling ASPM\n");
+		pcie_no_aspm();
 	}
 
 	pci_acpi_add_bus_pm_notifier(device, root->bus);