Message-ID: <4634097.MXvnqpQKZr@vostro.rjw.lan>
Date:	Fri, 23 Aug 2013 23:40:52 +0200
From:	"Rafael J. Wysocki" <rjw@...k.pl>
To:	Bjorn Helgaas <bhelgaas@...gle.com>
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 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?

> But if you want to merge a patch along the lines of what Neil
> proposes, I won't object.

I'm not sure what to do really, so I'm asking. :-)

Rafael


> >> > 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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