On the Haswell-based server (Grantley platform), there are two PCI
root bridges. One is the PCI-express root bridge (HID: PNP0A08)
for processor IIO devices, and the other is the PCI root bridge
(HID: PNP0A03) for the processor uncore devices.
Some BIOSes do not implement the _OSC object for PCI root bridge
(PNP0A03) since it is the optional object described on the page 286
of ACPI spec 5.0. This causes the variable no_aspm is set to 1 when
evaluating the undefined _OSC object of the PCI root bridge. It
turns out that the ASPM policy cannot be changed even though the
PCI-express root bridge on the Haswell-based server platform is
evaluated successfully. Here is the example:
$ cat /sys/module/pcie_aspm/parameters/policy
[default] performance powersave
$ echo performance | sudo tee /sys/module/pcie_aspm/parameters/policy
performance
tee: /sys/module/pcie_aspm/parameters/policy: Operation not permitted
To fix the above-mentioned issue, this patch does not set the
variable no_aspm to 1 if the returned status is AE_NOT_FOUND and
the bridge is the PCI root bridge.
After applying this patch, the ASPM policy can be changed correctly.
And, the corresponding reaction works correctly after changing a
policy.
Tested on the Grantley platform and v3.14-rc6.
Signed-off-by: Adrian Huang <ahuang12@xxxxxxxxxx>
---
drivers/acpi/pci_root.c | 7 +++++++
1 file changed, 7 insertions(+)
diff --git a/drivers/acpi/pci_root.c b/drivers/acpi/pci_root.c
index c1c4102..cfb3bca 100644
--- a/drivers/acpi/pci_root.c
+++ b/drivers/acpi/pci_root.c
@@ -446,6 +446,13 @@ 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)) {
+ if (status == AE_NOT_FOUND &&
+ !strcmp(acpi_device_hid(device), PCI_ROOT_HID_STRING)) {
+ dev_info(&device->dev,
+ "No _OSC; skip ASPM configuration\n");
+ return;
+ }
+
dev_info(&device->dev, "_OSC failed (%s); disabling ASPM\n",
acpi_format_exception(status));
*no_aspm = 1;
--
1.8.1.2
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