Date:	Fri, 23 Aug 2013 16:04:59 -0600
From:	Bjorn Helgaas <bhelgaas@...gle.com>
To:	"Rafael J. Wysocki" <rjw@...k.pl>
Cc:	Neil Horman <nhorman@...driver.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Len Brown <lenb@...nel.org>,
	"linux-acpi@...r.kernel.org" <linux-acpi@...r.kernel.org>,
	Yinghai Lu <yinghai@...nel.org>,
	Linux PCI <linux-pci@...r.kernel.org>
Subject: Re: [PATCH] ACPI: Fix osc flag setup ordering to allow pcie hotplug
 use when available

On Fri, Aug 23, 2013 at 3:40 PM, Rafael J. Wysocki <rjw@...k.pl> wrote:
> On Friday, August 23, 2013 02:46:23 PM Bjorn Helgaas wrote:
>> On Fri, Aug 23, 2013 at 2:53 PM, Rafael J. Wysocki <rjw@...k.pl> wrote:
>> > On Friday, August 23, 2013 04:05:11 PM Neil Horman wrote:
>> >> On Fri, Aug 23, 2013 at 09:38:18PM +0200, Rafael J. Wysocki wrote:
>> >> > [CCs added]
>> >> >
>> >> > Please always send PCI-related material to linux-pci in the first place.
>> >> >
>> >> Sorry, I ran get_maintainers and it seemed to think linux-acpi was sufficient.
>> >>
>> >> > The change that broke things for you was actually intentional:
>> >> >
>> >> > commit b8178f130e25c1bdac1c33e0996f1ff6e20ec08e
>> >> > Author: Bjorn Helgaas <bhelgaas@...gle.com>
>> >> > Date:   Mon Apr 1 15:47:39 2013 -0600
>> >> >
>> >> >     Revert "PCI/ACPI: Request _OSC control before scanning PCI root bus"
>> >> >
>> >> >     This reverts commit 8c33f51df406e1a1f7fa4e9b244845b7ebd61fa6.
>> >> >
>> >> > so I think we'll need to clean up the ASMP initialization after all.
>> >> >
>> >> Crud.  Reading over the revert commit, it seems like the problem boils down to
>> >> the odering of checking aspm_disabled.  It seems to me that the simple fix is to
>> >> track the desire for acpi to disable aspm separately from the users desire to
>> >> disable aspm (aspm_disabled).  Then we just turn the points where we check the
>> >> aspm_disabled into the appropriate or of two variables, except for
>> >> pcie_asmp_sanity_check, which remains sensitive to just the user disable option.
>> >>
>> >> Or is there more to this?
>> >
>> > No, I think you're right.
>> >
>> > Bjorn, what do you think?
>>
>> My opinion is that the _OSC/ASPM state management is ridiculously
>> complicated already, and this would make it slightly more complicated.
>>  That's why my preference would be to attempt a more radical cleanup
>> and simplification instead of adding another wart.
>
> Well, do you have anything specific in mind?

If I had a specific fix in mind, I would just post it, but I've never
had time to work through it all.  What I mean by complicated is that
every time I have to look at ASPM, I have to start by trying to figure
out the relationships between these variables:

    aspm_policy                 # default 0 (POLICY_DEFAULT)
                                  or POLICY_PERFORMANCE
                                  or POLICY_POWERSAVE depending on config
    aspm_disabled               # default 0
    aspm_force                  # default 0
    aspm_support_enabled        # default true

plus the _OSC-related code in acpi_pci_root_add(), which honestly is a
rat's nest.

It sounds like Neil's fix (while probably correct) would tangle that
nest a little more.  But I guess it would make sense to see the actual
patch and the justification (a regression fix, I suppose, but the
details weren't clear to me) before deciding.

>> >> > On Friday, August 23, 2013 01:19:39 PM 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@...driver.com>
>> >> > > CC: Len Brown <lenb@...nel.org>
>> >> > > CC: "Rafael J. Wysocki" <rjw@...k.pl>
>> >> > > CC: linux-acpi@...r.kernel.org
>> >> > > ---
>> >> > >  drivers/acpi/pci_root.c | 41 ++++++++++++++++++++---------------------
>> >> > >  1 file changed, 20 insertions(+), 21 deletions(-)
>> >> > >
>> >> > > diff --git a/drivers/acpi/pci_root.c b/drivers/acpi/pci_root.c
>> >> > > index 5917839..a2c2661 100644
>> >> > > --- a/drivers/acpi/pci_root.c
>> >> > > +++ b/drivers/acpi/pci_root.c
>> >> > > @@ -437,27 +437,6 @@ 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()) {
>> >> > > @@ -520,6 +499,26 @@ 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;
>> >> > > + }
>> >> > > +
>> >> > >   pci_acpi_add_bus_pm_notifier(device, root->bus);
>> >> > >   if (device->wakeup.flags.run_wake)
>> >> > >           device_set_run_wake(root->bus->bridge, true);
>> >> > >
>> >>
>> > --
>> > I speak only for myself.
>> > Rafael J. Wysocki, Intel Open Source Technology Center.
> --
> I speak only for myself.
> Rafael J. Wysocki, Intel Open Source Technology Center.
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