linux-kernel - Re: [PATCH v3] ACPI: Fix osc flag setup ordering to allow pcie hotplug use when available

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Date:	Wed, 28 Aug 2013 09:23:33 -0400
From:	Neil Horman <nhorman@...driver.com>
To:	Bjorn Helgaas <bhelgaas@...gle.com>
Cc:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Len Brown <lenb@...nel.org>, "Rafael J. Wysocki" <rjw@...k.pl>,
	"linux-acpi@...r.kernel.org" <linux-acpi@...r.kernel.org>,
	"linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
	Stefan Seyfried <stefan.seyfried@...glemail.com>
Subject: Re: [PATCH v3] ACPI: Fix osc flag setup ordering to allow pcie
 hotplug use when available

On Wed, Aug 28, 2013 at 07:04:47AM -0600, Bjorn Helgaas wrote:
> On Tue, Aug 27, 2013 at 5:43 PM, Neil Horman <nhorman@...driver.com> wrote:
> > On Tue, Aug 27, 2013 at 03:34:11PM -0600, Bjorn Helgaas wrote:
> >> [+cc Stefan]
> >>
> >> On Mon, Aug 26, 2013 at 9:39 AM, Neil Horman <nhorman@...driver.com> 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.
> >>
> > Yes, that bug is precisely what I am trying to fix (although your wording above is
> > inverted from the problem in the bug).  What happens is that acpiphp claims the
> > pcie ports, because acpiphp init runs first, and we haven't yet parsed _OSC,
> > which would have told acpiphp to yield control to pciehp.  The initial fix I
> > proposed fixed this by parsing _OSC prior to running the acpiphp bus scan, but
> > that reintroduced the problem of not handling pcie 1.1 aspm properly.  That has
> > been fixed in v2/v3 by deferring the setting of aspm_disable until after the bus
> > scan.
> >
> > Shall I submit a v4 with an updated changelog?
> 
> No need, I'll update the changelog and include the bugzilla reference
> and post it for your approval.  Thanks!
> 
> Bjorn
> 
Great, thanks!
Neil

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