PCI: Don't clear ASPM bits when the FADT declares it's unsupported

Communications with a hardware vendor confirm that the expected behaviour
on systems that set the FADT ASPM disable bit but which still grant full
PCIe control is for the OS to leave any BIOS configuration intact and
refuse to touch the ASPM bits.  This mimics the behaviour of Windows.
Signed-off-by: Matthew Garrett <mjg59@coreos.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>

drivers/acpi/pci_root.c

@@ -423,8 +423,7 @@ acpi_status acpi_pci_osc_control_set(acpi_handle handle, u32 *mask, u32 req)
 }
 EXPORT_SYMBOL(acpi_pci_osc_control_set);
 
-static void negotiate_os_control(struct acpi_pci_root *root, int *no_aspm,
-				 int *clear_aspm)
+static void negotiate_os_control(struct acpi_pci_root *root, int *no_aspm)
 {
 	u32 support, control, requested;
 	acpi_status status;
@@ -495,10 +494,12 @@ static void negotiate_os_control(struct acpi_pci_root *root, int *no_aspm,
 		decode_osc_control(root, "OS now controls", control);
 		if (acpi_gbl_FADT.boot_flags & ACPI_FADT_NO_ASPM) {
 			/*
-			 * We have ASPM control, but the FADT indicates
-			 * that it's unsupported. Clear it.
+			 * We have ASPM control, but the FADT indicates that
+			 * it's unsupported. Leave existing configuration
+			 * intact and prevent the OS from touching it.
 			 */
-			*clear_aspm = 1;
+			dev_info(&device->dev, "FADT indicates ASPM is unsupported, using BIOS configuration\n");
+			*no_aspm = 1;
 		}
 	} else {
 		decode_osc_control(root, "OS requested", requested);
@@ -525,7 +526,7 @@ static int acpi_pci_root_add(struct acpi_device *device,
 	int result;
 	struct acpi_pci_root *root;
 	acpi_handle handle = device->handle;
-	int no_aspm = 0, clear_aspm = 0;
+	int no_aspm = 0;
 	bool hotadd = system_state != SYSTEM_BOOTING;
 
 	root = kzalloc(sizeof(struct acpi_pci_root), GFP_KERNEL);
@@ -584,7 +585,7 @@ static int acpi_pci_root_add(struct acpi_device *device,
 
 	root->mcfg_addr = acpi_pci_root_get_mcfg_addr(handle);
 
-	negotiate_os_control(root, &no_aspm, &clear_aspm);
+	negotiate_os_control(root, &no_aspm);
 
 	/*
 	 * TBD: Need PCI interface for enumeration/configuration of roots.
@@ -607,10 +608,6 @@ static int acpi_pci_root_add(struct acpi_device *device,
 		goto remove_dmar;
 	}
 
-	if (clear_aspm) {
-		dev_info(&device->dev, "Disabling ASPM (FADT indicates it is unsupported)\n");
-		pcie_clear_aspm(root->bus);
-	}
 	if (no_aspm)
 		pcie_no_aspm();
 

drivers/pci/pcie/aspm.c

@@ -782,24 +782,6 @@ void pci_disable_link_state(struct pci_dev *pdev, int state)
 }
 EXPORT_SYMBOL(pci_disable_link_state);
 
-void pcie_clear_aspm(struct pci_bus *bus)
-{
-	struct pci_dev *child;
-
-	if (aspm_force)
-		return;
-
-	/*
-	 * Clear any ASPM setup that the firmware has carried out on this bus
-	 */
-	list_for_each_entry(child, &bus->devices, bus_list) {
-		__pci_disable_link_state(child, PCIE_LINK_STATE_L0S |
-					 PCIE_LINK_STATE_L1 |
-					 PCIE_LINK_STATE_CLKPM,
-					 false, true);
-	}
-}
-
 static int pcie_aspm_set_policy(const char *val, struct kernel_param *kp)
 {
 	int i;

include/linux/pci-aspm.h

@@ -29,7 +29,6 @@ void pcie_aspm_pm_state_change(struct pci_dev *pdev);
 void pcie_aspm_powersave_config_link(struct pci_dev *pdev);
 void pci_disable_link_state(struct pci_dev *pdev, int state);
 void pci_disable_link_state_locked(struct pci_dev *pdev, int state);
-void pcie_clear_aspm(struct pci_bus *bus);
 void pcie_no_aspm(void);
 #else
 static inline void pcie_aspm_init_link_state(struct pci_dev *pdev)
@@ -47,9 +46,6 @@ static inline void pcie_aspm_powersave_config_link(struct pci_dev *pdev)
 static inline void pci_disable_link_state(struct pci_dev *pdev, int state)
 {
 }
-static inline void pcie_clear_aspm(struct pci_bus *bus)
-{
-}
 static inline void pcie_no_aspm(void)
 {
 }