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Date: Fri, 18 May 2018 08:07:26 -0500
From: Bjorn Helgaas <helgaas@kernel.org>
To: "Rafael J. Wysocki" <rjw@rjwysocki.net>
Cc: Bjorn Helgaas <bhelgaas@google.com>, Len Brown <lenb@kernel.org>,
        Mario.Limonciello@dell.com,
        Michael Jamet <michael.jamet@intel.com>,
        Yehezkel Bernat <YehezkelShB@gmail.com>,
        Andy Shevchenko <andriy.shevchenko@linux.intel.com>,
        Lukas Wunner <lukas@wunner.de>, linux-pci@vger.kernel.org,
        linux-acpi@vger.kernel.org,
        Mika Westerberg <mika.westerberg@linux.intel.com>
Subject: Re: [PATCH v7 03/12] PCI: Request control of native PCIe hotplug
 only if supported
Message-ID: <20180518130726.GA41790@bhelgaas-glaptop.roam.corp.google.com>
References: <20180517092903.43701-1-mika.westerberg@linux.intel.com>
 <20180517092903.43701-4-mika.westerberg@linux.intel.com>
 <20180517141324.GD19955@bhelgaas-glaptop.roam.corp.google.com>
 <1570821.OC5yac8T6J@aspire.rjw.lan>
 <20180518125706.GA34002@bhelgaas-glaptop.roam.corp.google.com>
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On Fri, May 18, 2018 at 07:57:07AM -0500, Bjorn Helgaas wrote:
> On Fri, May 18, 2018 at 09:48:54AM +0200, Rafael J. Wysocki wrote:
> > On Thursday, May 17, 2018 4:13:24 PM CEST Bjorn Helgaas wrote:
> > > On Thu, May 17, 2018 at 12:28:54PM +0300, Mika Westerberg wrote:
> 
> > > >  	host_bridge = to_pci_host_bridge(bus->bridge);
> > > >  	if (!(root->osc_control_set & OSC_PCI_EXPRESS_NATIVE_HP_CONTROL))
> > > > -		host_bridge->native_hotplug = 0;
> > > > +		host_bridge->native_pcie_hotplug = 0;
> > > >  	if (!(root->osc_control_set & OSC_PCI_EXPRESS_AER_CONTROL))
> > > >  		host_bridge->native_aer = 0;
> > > >  	if (!(root->osc_control_set & OSC_PCI_EXPRESS_PME_CONTROL))
> > > 
> > > Rafael, I noticed that the PCI Firmware Spec, r3.2, sec 4.5.2.2, says
> > > we're required to evaluate _OSC when resuming from S4.  I don't see a
> > > path where we do that today.
> > 
> > No, we don't do that today.
> > 
> > > Am I missing it?  If not, what resume hook do we need to use to do
> > > this?
> > 
> > We could do that in the ->restore_noirq callback of the host bridge
> > device I suppose.  Basically, before resuming all of the PCI devices
> > on the bus.
> > 
> > However, question is on what conditions.  Do the previous versions of the
> > spec have this requirement or is it just a new thing?
> 
> I think the requirement has been there since the beginning of _OSC.
> The first reference I can find is ACPI 3.0, sec 6.2.9, which says we
> should evaluate _OSC on wake from S4 and when a Notify(<device>, 8) is
> delivered.  AFAICT, this applies to all _OSC methods, not just those
> for PCI host bridges.
> 
> The OSHP description (PCI Firmware Spec r3.2, sec 4.8) talks about
> interrupt reconfiguration that may be needed when the OS takes over
> control of SHPC.  I assume this kind of reconfiguration needs to be
> done on wake from S4.

Forgot to mention: I wonder if this omission could be related to mysterious
resume issues like https://bugzilla.kernel.org/show_bug.cgi?id=99751