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>

1 files changed, 8 insertions, 11 deletions

diff --git a/drivers/acpi/pci_root.c b/drivers/acpi/pci_root.c
index 68a5f712cd19..1b5569c092c6 100644
--- a/drivers/acpi/pci_root.c
+++ b/drivers/acpi/pci_root.c
@@ -423,8 +423,7 @@ out:
 }
 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();