On Thu, Aug 29, 2013 at 11:47:13AM -0600, Bjorn Helgaas wrote:
> On Mon, Aug 26, 2013 at 11:39:13AM -0400, Neil Horman 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.
> >
> > 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);
>
> I think there are two problems with this patch:
>
> 1) There's another call of pcie_no_aspm() at line 454 (in the
> error path when acpi_pci_osc_support() fails), which happens
> before scanning the bus. I think this needs to be converted to
> "no_aspm = true" as you did for the one in the error path when
> acpi_pci_osc_control_set() fails.
>
I was wondering about that. I left it alone because this patch didn't introduce
that condition (callingpcie_no_aspm at line 454). I thought perhaps there was
something there I didn't completely understand, but yes, I agree, it seems like
it should use the no_aspm just like the call I converted.
> 2) You effectively moved the call of "pcie_clear_aspm(root->bus)"
> so it now happens before scanning the bus, which will cause a
> NULL pointer dereference if we take that path.
>
Yes, you're correct, and I missed that, we need to defer that call just like we
do with pcie_no_aspm.
> I think we need something like the patch below on top of your
> v3 patch. Can you take a look and see if this makes sense, and
> if so, update your patch to include these or similar fixes?
>
I agree, I'll send a v4 tomorrow, with these changes incorporated, and an
updated changelog reflecting the exact problem we're solving here.
Thanks!
Neil
> Here are my notes about where the ASPM and root->osc_control_set
> setting and testing happen.
>
> Before your patch:
>
> acpi_pci_root_add
> root = kzalloc # root->osc_control_set = 0
> acpi_pci_osc_support # indicate OS support for segments
> root->bus = pci_acpi_scan_root # SCAN BUS
> pci_create_root_bus
> pcibios_add_bus
> acpi_pci_add_bus
> acpiphp_enumerate_slots
> acpi_walk_namespace(..., register_slot, ...)
> register_slot
> device_is_managed_by_native_pciehp
> <test root->osc_control_set> # root->osc_control_set == 0
> return if OS has PCIe hotplug control (we never do)
> acpiphp_register_hotplug_slot (so we always do this)
> acpi_pci_osc_support # indicate OS support for MSI, ASPM, etc
> if (_osc_support() failed)
> pci_no_aspm
> acpi_pci_osc_control_set # request OS control of hotplug, PME, AER, etc
> root->osc_control_set = XX
> if (_osc_control_set() succeeded) {
> if (FADT NO_ASPM bit)
> pcie_clear_aspm
> list_for_each_entry(..., &bus->devices, ...)
> } else
> pcie_no_aspm # _osc_control_set() failed
>
> After your patch:
>
> acpi_pci_root_add
> root = kzalloc # root->osc_control_set = 0
> acpi_pci_osc_support # indicate OS support for segments
> if (_osc_support() failed)
> pci_no_aspm # ** (1) before bus scan
> acpi_pci_osc_support # indicate OS support for MSI, ASPM, etc
> acpi_pci_osc_control_set # request OS control of hotplug, PME, AER, etc
> root->osc_control_set = XX
> if (_osc_control_set() succeeded) {
> if (FADT NO_ASPM bit)
> pcie_clear_aspm(root->bus) # ** (2) root->bus == NULL
> list_for_each_entry(..., &bus->devices, ...)
> } else
> no_aspm = true # _osc_control_set() failed
> root->bus = pci_acpi_scan_root # SCAN BUS
> pci_create_root_bus
> pcibios_add_bus
> acpi_pci_add_bus
> acpiphp_enumerate_slots
> acpi_walk_namespace(..., register_slot, ...)
> register_slot
> device_is_managed_by_native_pciehp
> <test root->osc_control_set>
> return if OS has PCIe hotplug control
> acpiphp_register_hotplug_slot
> if (no_aspm)
> pcie_no_aspm
>
>
> Bjorn
>
>
> diff --git a/drivers/acpi/pci_root.c b/drivers/acpi/pci_root.c
> index a37a372..a67853e 100644
> --- a/drivers/acpi/pci_root.c
> +++ b/drivers/acpi/pci_root.c
> @@ -378,7 +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;
> + bool no_aspm = false, clear_aspm = false;
>
> root = kzalloc(sizeof(struct acpi_pci_root), GFP_KERNEL);
> if (!root)
> @@ -451,7 +451,7 @@ static int acpi_pci_root_add(struct acpi_device *device,
> if (ACPI_FAILURE(status)) {
> dev_info(&device->dev, "ACPI _OSC support "
> "notification failed, disabling PCIe ASPM\n");
> - pcie_no_aspm();
> + no_aspm = true;
> flags = base_flags;
> }
> }
> @@ -483,7 +483,7 @@ static int acpi_pci_root_add(struct acpi_device *device,
> * We have ASPM control, but the FADT indicates
> * that it's unsupported. Clear it.
> */
> - pcie_clear_aspm(root->bus);
> + clear_aspm = true;
> }
> } else {
> dev_info(&device->dev,
> @@ -527,6 +527,10 @@ static int acpi_pci_root_add(struct acpi_device *device,
> goto end;
> }
>
> + if (clear_aspm) {
> + dev_info(&device->dev, "Disabling ASPM (FADT indicates it is unsupported)\n");
> + pcie_clear_aspm(root->bus);
> + }
> if (no_aspm)
> pcie_no_aspm();
>
>
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