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

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Message-ID: <20130823200511.GB632@hmsreliant.think-freely.org>
Date:	Fri, 23 Aug 2013 16:05:11 -0400
From:	Neil Horman <nhorman@...driver.com>
To:	"Rafael J. Wysocki" <rjw@...k.pl>
Cc:	linux-kernel@...r.kernel.org, Len Brown <lenb@...nel.org>,
	linux-acpi@...r.kernel.org, Bjorn Helgaas <bhelgaas@...gle.com>,
	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 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?

Neil

> 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.
> 
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