Re: [PATCH v3] ACPI: Fix osc flag setup ordering to allow pciehotplug use when available

From: Bjorn Helgaas
Date: Tue Aug 27 2013 - 17:34:39 EST

[+cc Stefan]

On Mon, Aug 26, 2013 at 9:39 AM, Neil Horman <nhorman@xxxxxxxxxxxxx> wrote:
> Somewhere between 3.9 and 3.10 it seems the order in which pcie and acpi probed
> slots for hotplug capabilites got reversed. While this isn't a big deal, it did
> uncover a bug in the ACPI bus setup path. Specifically, acpi_pci_root_add calls
> pci_acpi_scan_root before setting the osc flags for the device handle.
> pci_acpi_scan_root, among other things uses device_is_managed_by_native_pciehp()
> to determine if a given slot has pcie hotplug capabilties, whcih checks the
> devices OSC_PCI_EXPRESS_NATIVE_HP_CONTROL flag. Since that flag is not set
> until after pci_acpi_scan_root_completes, the acpi code never sees that pcie
> slots are hotplug capable and configures them all to use acpi instead.

I'd like to make it more explicit what we're fixing. Apparently this
is a regression between v3.9 and v3.10.

Is this a fix for problems like
https://bugzilla.kernel.org/show_bug.cgi?id=60736 ? That bug is that
an ExpressCard slot doesn't work unless we boot with
"acpiphp.disable=1". I think what happens there is that acpiphp
claims the slot before we run _OSC, so pciehp doesn't claim it, even
though _OSC did grant us control over native PCIe hotplug.

> Fix is pretty simple, just defer the scan until after the osc flags have been
> set on the device. Tested by myself and it seems to work well.
>
> Signed-off-by: Neil Horman <nhorman@xxxxxxxxxxxxx>
> CC: Len Brown <lenb@xxxxxxxxxx>
> CC: "Rafael J. Wysocki" <rjw@xxxxxxx>
> CC: Bjorn Helgaas <bhelgaas@xxxxxxxxxx>
> CC: linux-acpi@xxxxxxxxxxxxxxx
> CC: linux-pci@xxxxxxxxxxxxxxx
>
> ---
> Change notes:
> v2) eferred the disabling of aspm until after the acpi scan of the pci bus is
> complete. This was done to allow proper handling of pcie 1.1 devices, as per:
>
> commit b8178f130e25c1bdac1c33e0996f1ff6e20ec08e
> Author: Bjorn Helgaas <bhelgaas@xxxxxxxxxx>
> Date: Mon Apr 1 15:47:39 2013 -0600
>
> Revert "PCI/ACPI: Request _OSC control before scanning PCI root bus"
>
> As discussed previously in the thread the disable logic for aspm needs to be
> untangled and refactored, which is not something I'm sufficently versed in teh
> hotplug code to do right now, but this fixes the problem above, and prevents the
> problem that necessitated the revert without adding any visible complexity to
> the user, so I think its ok.
>
> v3) Fixup stupid authorship error
> ---
> drivers/acpi/pci_root.c | 54 +++++++++++++++++++++++++++++--------------------
> 1 file changed, 32 insertions(+), 22 deletions(-)
>
> diff --git a/drivers/acpi/pci_root.c b/drivers/acpi/pci_root.c
> index 5917839..1e80a90 100644
> --- a/drivers/acpi/pci_root.c
> +++ b/drivers/acpi/pci_root.c
> @@ -378,6 +378,7 @@ static int acpi_pci_root_add(struct acpi_device *device,
> struct acpi_pci_root *root;
> u32 flags, base_flags;
> acpi_handle handle = device->handle;
> + bool no_aspm = false;
>
> root = kzalloc(sizeof(struct acpi_pci_root), GFP_KERNEL);
> if (!root)
> @@ -437,27 +438,6 @@ static int acpi_pci_root_add(struct acpi_device *device,
> flags = base_flags = OSC_PCI_SEGMENT_GROUPS_SUPPORT;
> acpi_pci_osc_support(root, flags);
>
> - /*
> - * TBD: Need PCI interface for enumeration/configuration of roots.
> - */
> -
> - /*
> - * Scan the Root Bridge
> - * --------------------
> - * Must do this prior to any attempt to bind the root device, as the
> - * PCI namespace does not get created until this call is made (and
> - * thus the root bridge's pci_dev does not exist).
> - */
> - root->bus = pci_acpi_scan_root(root);
> - if (!root->bus) {
> - dev_err(&device->dev,
> - "Bus %04x:%02x not present in PCI namespace\n",
> - root->segment, (unsigned int)root->secondary.start);
> - result = -ENODEV;
> - goto end;
> - }
> -
> - /* Indicate support for various _OSC capabilities. */
> if (pci_ext_cfg_avail())
> flags |= OSC_EXT_PCI_CONFIG_SUPPORT;
> if (pcie_aspm_support_enabled()) {
> @@ -512,7 +492,14 @@ static int acpi_pci_root_add(struct acpi_device *device,
> acpi_format_exception(status), flags);
> dev_info(&device->dev,
> "ACPI _OSC control for PCIe not granted, disabling ASPM\n");
> - pcie_no_aspm();
> + /*
> + * We want to disable aspm here, but aspm_disabled
> + * needs to remain in its state from boot so that we
> + * properly handle pcie 1.1 devices. So we set this
> + * flag here, to defer the action until after the acpi
> + * root scan
> + */
> + no_aspm = true;
> }
> } else {
> dev_info(&device->dev,
> @@ -520,6 +507,29 @@ static int acpi_pci_root_add(struct acpi_device *device,
> "(_OSC support mask: 0x%02x)\n", flags);
> }
>
> + /*
> + * TBD: Need PCI interface for enumeration/configuration of roots.
> + */
> +
> + /*
> + * Scan the Root Bridge
> + * --------------------
> + * Must do this prior to any attempt to bind the root device, as the
> + * PCI namespace does not get created until this call is made (and
> + * thus the root bridge's pci_dev does not exist).
> + */
> + root->bus = pci_acpi_scan_root(root);
> + if (!root->bus) {
> + dev_err(&device->dev,
> + "Bus %04x:%02x not present in PCI namespace\n",
> + root->segment, (unsigned int)root->secondary.start);
> + result = -ENODEV;
> + goto end;
> + }
> +
> + if (no_aspm)
> + 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);
> --
> 1.8.1.4
>
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/