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

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Date:	Wed, 15 Aug 2012 13:47:23 -0600
From:	Bjorn Helgaas <bhelgaas@...gle.com>
To:	"Rafael J. Wysocki" <rjw@...k.pl>, Len Brown <lenb@...nel.org>
Cc:	ACPI Devel Mailing List <linux-acpi@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>, linux-pci@...r.kernel.org,
	Wei Kong <wkong@...ell.com>, Jean Delvare <jdelvare@...e.com>,
	Matthew Garrett <mjg59@...f.ucam.org>
Subject: Re: [PATCH] PCI / ACPI: Do not request control of ASPM if the BIOS
 has disabled it

On Thu, May 24, 2012 at 2:45 PM, Rafael J. Wysocki <rjw@...k.pl> wrote:
> 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.

Len, since you've applied recent patches in this area, can you take
care of this, too?

> ---
>  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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