PCI/ACPI: Allow _OSC presence to be optional for PCI

The PCI Firmware Spec, r3.2, sec 4.5.1, says:

  For a host bridge device that originates a PCI Express hierarchy, the
  _OSC interface defined in this section is required.  For a host bridge
  device that originates a PCI/PCI-X bus hierarchy, inclusion of an _OSC
  object is optional.

Allow PCI host bridges to bail out silently if _OSC is not found.

Reported-by: Michael Kelley <mikelley@microsoft.com>
Signed-off-by: Sinan Kaya <okaya@kernel.org>
[bhelgaas: cite PCI Firmware spec, the authoritative source]
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>

1 files changed, 11 insertions, 3 deletions

diff --git a/drivers/acpi/pci_root.c b/drivers/acpi/pci_root.c
index e465e720eab2..707aafc7c2aa 100644
--- a/drivers/acpi/pci_root.c
+++ b/drivers/acpi/pci_root.c
@@ -421,7 +421,8 @@ out:
 }
 EXPORT_SYMBOL(acpi_pci_osc_control_set);
 
-static void negotiate_os_control(struct acpi_pci_root *root, int *no_aspm)
+static void negotiate_os_control(struct acpi_pci_root *root, int *no_aspm,
+                                 bool is_pcie)
 {
         u32 support, control, requested;
         acpi_status status;
@@ -455,10 +456,15 @@ static void negotiate_os_control(struct acpi_pci_root *root, int *no_aspm)
         decode_osc_support(root, "OS supports", support);
         status = acpi_pci_osc_support(root, support);
         if (ACPI_FAILURE(status)) {
+                *no_aspm = 1;
+
+                /* _OSC is optional for PCI host bridges */
+                if ((status == AE_NOT_FOUND) && !is_pcie)
+                        return;
+
                 dev_info(&device->dev, "_OSC failed (%s)%s\n",
                          acpi_format_exception(status),
                          pcie_aspm_support_enabled() ? "; disabling ASPM" : "");
-                *no_aspm = 1;
                 return;
         }
 
@@ -534,6 +540,7 @@ static int acpi_pci_root_add(struct acpi_device *device,
         acpi_handle handle = device->handle;
         int no_aspm = 0;
         bool hotadd = system_state == SYSTEM_RUNNING;
+        bool is_pcie;
 
         root = kzalloc(sizeof(struct acpi_pci_root), GFP_KERNEL);
         if (!root)
@@ -591,7 +598,8 @@ 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);
+        is_pcie = strcmp(acpi_device_hid(device), "PNP0A08") == 0;
+        negotiate_os_control(root, &no_aspm, is_pcie);
 
         /*
          * TBD: Need PCI interface for enumeration/configuration of roots.