From: Matthew Garrett <mjg@redhat.com>

Subject: ACPI: Disable ASPM if the platform won't provide _OSC control for PCIe

ACPI: Disable ASPM if the platform won't provide _OSC control for PCIe

The PCI SIG documentation for the _OSC OS/firmware handshaking interface

states:

"If the _OSC control method is absent from the scope of a host bridge

device, then the operating system must not enable or attempt to use any

features defined in this section for the hierarchy originated by the host

bridge."

The obvious interpretation of this is that the OS should not attempt to use

PCIe hotplug, PME or AER - however, the specification also notes that an

_OSC method is *required* for PCIe hierarchies, and experimental validation

with An Alternative OS indicates that it doesn't use any PCIe functionality

if the _OSC method is missing. That arguably means we shouldn't be using

MSI or extended config space, but right now our problems seem to be limited

to vendors being surprised when ASPM gets enabled on machines when other

OSs refuse to do so. So, for now, let's just disable ASPM if the _OSC

method doesn't exist or refuses to hand over PCIe capability control.

Signed-off-by: Matthew Garrett <mjg@redhat.com>

---

diff --git a/drivers/acpi/pci_root.c b/drivers/acpi/pci_root.c

index 4eac593..1f67057 100644

--- a/drivers/acpi/pci_root.c

+++ b/drivers/acpi/pci_root.c

@@ -33,6 +33,7 @@

 #include <linux/pm_runtime.h>

 #include <linux/pci.h>

 #include <linux/pci-acpi.h>

+#include <linux/pci-aspm.h>

 #include <linux/acpi.h>

 #include <linux/slab.h>

 #include <acpi/acpi_bus.h>

@@ -543,6 +544,14 @@ static int __devinit acpi_pci_root_add(struct acpi_device *device)

 	if (flags != base_flags)

 		acpi_pci_osc_support(root, flags);

+	status = acpi_pci_osc_control_set(root->device->handle,

+					  0);

+

+	if (status == AE_NOT_EXIST) {

+		printk(KERN_INFO "Unable to assume PCIe control: Disabling ASPM\n");

+		pcie_no_aspm();

+	}

+

 	pci_acpi_add_bus_pm_notifier(device, root->bus);

 	if (device->wakeup.flags.run_wake)

 		device_set_run_wake(root->bus->bridge, true);