From: Rafael J. Wysocki on
On Tuesday, June 22, 2010, Matthew Garrett wrote:
> 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(a)redhat.com>

Acked-by: Rafael J. Wysocki <rjw(a)sisk.pl>

> ---
> drivers/acpi/pci_root.c | 9 +++++++++
> 1 files changed, 9 insertions(+), 0 deletions(-)
>
> diff --git a/drivers/acpi/pci_root.c b/drivers/acpi/pci_root.c
> index 1af8081..7167213 100644
> --- a/drivers/acpi/pci_root.c
> +++ b/drivers/acpi/pci_root.c
> @@ -32,6 +32,7 @@
> #include <linux/pm.h>
> #include <linux/pci.h>
> #include <linux/pci-acpi.h>
> +#include <linux/pci-aspm.h>
> #include <linux/acpi.h>
> #include <acpi/acpi_bus.h>
> #include <acpi/acpi_drivers.h>
> @@ -576,6 +577,14 @@ 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,
> + OSC_PCI_EXPRESS_CAP_STRUCTURE_CONTROL);
> +
> + if (ACPI_FAILURE(status)) {
> + printk(KERN_INFO "Unable to assume PCIe control: Disabling ASPM\n");
> + pcie_no_aspm();
> + }
> +
> return 0;
>
> end:
>

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo(a)vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
From: Rafael J. Wysocki on
On Tuesday, June 22, 2010, Jesse Barnes wrote:
> On Tue, 22 Jun 2010 20:17:29 +0200
> "Rafael J. Wysocki" <rjw(a)sisk.pl> wrote:
>
> > On Tuesday, June 22, 2010, Matthew Garrett wrote:
> > > 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(a)redhat.com>
> >
> > Acked-by: Rafael J. Wysocki <rjw(a)sisk.pl>
>
> Applied to my linux-next branch, thanks.

I think it's 2.6.35 (and probably -stable) material, these problems aleady
happen in the field.

Matthew, what do you think?

Rafael
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo(a)vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/