ACPI Spec 6.0 Section 6.2.11.3 OSC Implementation Example for PCI
Host Bridge Devices:

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.

Signed-off-by: Sinan Kaya <ok...@kernel.org>
Reported-by: Michael Kelley <mikel...@microsoft.com>
---
 drivers/acpi/pci_root.c | 14 +++++++++++---
 1 file changed, 11 insertions(+), 3 deletions(-)

diff --git a/drivers/acpi/pci_root.c b/drivers/acpi/pci_root.c
index e465e72..707aafc 100644
--- a/drivers/acpi/pci_root.c
+++ b/drivers/acpi/pci_root.c
@@ -421,7 +421,8 @@ 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)
+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.
-- 
2.7.4

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