linux-kernel - [PATCH] PCI / ACPI: Do not request control of ASPM if the BIOS has disabled it

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Date:	Thu, 24 May 2012 22:45:45 +0200
From:	"Rafael J. Wysocki" <rjw@...k.pl>
To:	Bjorn Helgaas <bhelgaas@...gle.com>
Cc:	ACPI Devel Mailing List <linux-acpi@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>, linux-pci@...r.kernel.org,
	Len Brown <lenb@...nel.org>, Wei Kong <wkong@...ell.com>,
	Jean Delvare <jdelvare@...e.com>,
	Matthew Garrett <mjg59@...f.ucam.org>
Subject: [PATCH] PCI / ACPI: Do not request control of ASPM if the BIOS has disabled it

From: Rafael J. Wysocki <rjw@...k.pl>

We want to report that the kernel supports ASPM to the BIOS even if
the BIOS signals us that it doesn't.  So, we need the flags to include
(OSC_ACTIVE_STATE_PWR_SUPPORT | OSC_CLOCK_PWR_CAPABILITY_SUPPORT)
before calling acpi_pci_osc_support(root, flags) in
acpi_pci_root_add() (unless there's a command line telling us that
ASPM is not to be supported).

However, knowing that the BIOS doesn't support ASPM, we shouldn't
request the control of it, so we should remove
(OSC_ACTIVE_STATE_PWR_SUPPORT | OSC_CLOCK_PWR_CAPABILITY_SUPPORT)
from the flags before calling acpi_pci_osc_control_set() in those
cases.  Failing to do so causes the evaluation of _OSC for the PCI
root bridge to return error codes on some systems where it should
work correctly.

Reported-and-tested-by: Wei Kong <wkong@...ell.com>
Signed-off-by: Rafael J. Wysocki <rjw@...k.pl>
---

-stable material, I think.

Thanks,
Rafael

---
 drivers/acpi/pci_root.c |    4 ++++
 1 file changed, 4 insertions(+)

Index: linux/drivers/acpi/pci_root.c
===================================================================
--- linux.orig/drivers/acpi/pci_root.c
+++ linux/drivers/acpi/pci_root.c
@@ -574,6 +574,10 @@ static int __devinit acpi_pci_root_add(s
 	if (flags != base_flags)
 		acpi_pci_osc_support(root, flags);

+	if (!pcie_aspm_enabled())
+		flags &= ~(OSC_ACTIVE_STATE_PWR_SUPPORT |
+			OSC_CLOCK_PWR_CAPABILITY_SUPPORT);
+
 	if (!pcie_ports_disabled
 	    && (flags & ACPI_PCIE_REQ_SUPPORT) == ACPI_PCIE_REQ_SUPPORT) {
 		flags = OSC_PCI_EXPRESS_CAP_STRUCTURE_CONTROL
--
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