Date:	Mon, 13 Apr 2015 14:04:22 +0200
From:	"Rafael J. Wysocki" <rjw@...ysocki.net>
To:	Jiang Liu <jiang.liu@...ux.intel.com>
Cc:	"Rafael J. Wysocki" <rafael@...nel.org>,
	Bjorn Helgaas <bhelgaas@...gle.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	"x86@...nel.org" <x86@...nel.org>, Len Brown <lenb@...nel.org>,
	Lv Zheng <lv.zheng@...el.com>,
	LKML <linux-kernel@...r.kernel.org>,
	"linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
	"linux-acpi@...r.kernel.org" <linux-acpi@...r.kernel.org>
Subject: Re: [Bugfix v3] x86/PCI/ACPI: Fix regression caused by commit 63f1789ec716

On Monday, April 13, 2015 12:31:20 PM Jiang Liu wrote:
> On 2015/4/10 8:28, Rafael J. Wysocki wrote:
> > On Fri, Apr 10, 2015 at 12:37 AM, Rafael J. Wysocki <rjw@...ysocki.net> wrote:
> >> On Thursday, April 09, 2015 05:00:08 PM Bjorn Helgaas wrote:
> >>> On Thu, Apr 9, 2015 at 4:37 PM, Rafael J. Wysocki <rjw@...ysocki.net> wrote:
> >>>> On Thursday, April 09, 2015 10:50:02 AM Jiang Liu wrote:
> >>>>> On 2015/4/9 7:44, Rafael J. Wysocki wrote:
> >>>>>> On Wednesday, April 08, 2015 01:48:46 PM Jiang Liu wrote:
> >>>>>>> On 2015/4/7 8:28, Rafael J. Wysocki wrote:
> >>>>>>>> On Friday, April 03, 2015 10:04:11 PM Bjorn Helgaas wrote:
> >>>>>>>>> Hi Jiang,
> >>>>>>> <snip>
> >>>>>>>>>> Currently acpi_dev_filter_resource_type() is only used by ACPI pci
> >>>>>>>>>> host bridge and IOAPIC driver, so it shouldn't affect other drivers.
> >>>>>>>>>
> >>>>>>>>> We should assume it will eventually be used for all ACPI devices,
> >>>>>>>>> shouldn't we?
> >>>>>>>>
> >>>>>>>> I'm not sure about that, really.  In fact, I'd restrict its use to devices
> >>>>>>>> types that actually can "produce" resources (ie. do not require the resources
> >>>>>>>> to be provided by their ancestors or to be available from a global pool).
> >>>>>>>>
> >>>>>>>> Otherwise we're pretty much guaranteed to get into trouble.
> >>>>>>>>
> >>>>>>>> And all of the above rules need to be documented in the kernel source tree
> >>>>>>>> or people will get confused.
> >>>>>>> Hi Rafael,
> >>>>>>>     How about following comments for acpi_dev_filter_resource_type()?
> >>>>>>> Thanks!
> >>>>>>> Gerry
> >>>>>>> --------------------------------------------------------------------
> >>>>>>> /**
> >>>>>>>  * According to ACPI specifications, Consumer/Producer flag in ACPI resource
> >>>>>>>  * descriptor means:
> >>>>>>>  *      1(CONSUMER): This device consumes this resource
> >>>>>>>  *      0(PRODUCER): This device produces and consumes this resource
> >>>>>>>  * But for ACPI PCI host bridge, it is interpreted in another way:
> >>>>>>
> >>>>>> So first of all, this leads to a question: Why is it interpreted for ACPI PCI
> >>>>>> host bridges differently?
> >>>>>>
> >>>>>> Is it something we've figured out from experience, or is there a standard
> >>>>>> mandating that?
> >>>>> Hi Rafael,
> >>>>>       I think we got this knowledge by experiences. PCI FW spec only
> >>>>> states _CRS reports resources assigned to the host bridge by firmware.
> >>>>> There's no statement about whether the resource is consumed by host
> >>>>> bridge itself or provided to it's child bus/devices. On x86/IA64 side,
> >>>>> the main resource consumed by PCI host bridge is IOPORT 0xCF8-0xCFF,
> >>>>> but not sure about ARM64 side. So how about:
> >>>>
> >>>> This:
> >>>>
> >>>>> PCI Firmware specification states that _CRS reports resources
> >>>>> assigned to the host bridge, but there's no way to tell whether
> >>>>> the resource is consumed by host bridge itself or provided to
> >>>>> its child bus/devices.
> >>>>
> >>>> looks OK to me, but I'd replace the below with something like:
> >>>>
> >>>> "However, experience shows, that in the PCI host bridge case firmware writers
> >>>>  expect the resource to be provided to devices on the bus (below the bridge) for
> >>>>  consumption entirely if its Consumer/Producer flag is clear.  That expectation
> >>>>  is reflected by the code in this routine as follows:".
> >>>
> >>> What a mess.  The spec is regrettably lacking in Consumer/Producer
> >>> specifics.  But I don't see what's confusing about the descriptors
> >>> that have Consumer/Producer bits.
> >>>
> >>> QWord, DWord, and Word descriptors don't seem to have a
> >>> Consumer/Producer bit, but they do contain _TRA, so they must be
> >>> intended for bridge windows.  Can they also be used for device
> >>> registers?  I don't know.
> >>>
> >>> The Extended Address descriptor has a Consumer/Producer bit, and I
> >>> would interpret the spec to mean that if the flag is clear (the device
> >>> produces and consumes this resource), the resource is available on the
> >>> bus below the bridge, i.e., the bridge consumes the resource on its
> >>> upstream side and produces it on its downstream side.
> >>
> >> OK, that makes sense for bridges.
> 
> >>> If the bit were
> >>> set (the device only consumes the resource), I would expect that to
> >>> mean the descriptor is for bridge registers like 0xcf8/0xcfc that
> >>> never appear on the downstream side.
> >>
> >> That part is clear.  What is not clear is whether or not we can *always*
> >> expect the resources with Consumer/Producer *clear* to be produced on the
> >> downstram side.  That appears to be the case for host bridges if my
> >> understanding of things is correct, but is it the case in general?
> >>
> >>> Maybe I'm reading the spec too naively, but this doesn't seem a matter
> >>> of experience.
> >>
> >> Well, the specification is not clear enough in that respect, at least as
> >> far as I can say, or maybe it is, but then does firmware always follow that
> >> interpretation?
> > 
> > So I guess I'd like to propose to go back to the 3.19 behavior for PCI host
> > bridges and then to handle the IOAPIC as a separate case.
> > 
> > We can think about consolidating the two later.
> > 
> > Any objections to doing that?
> Hi Rafael,
> 	When reverting to the behavior before v3.19, I found a simpler
> solution. The logic before v3.19 is:
> on x86 and IA64, all IO port and MMIO resources assigned to PCI host
> bridge are available to child bus/devices, except one special case to
> filter out IO port[0xCF8-0xCFF] for PCI configuration space access.
> 
> And with pre-v3.19 kernels, all IO port defined by IO and fixed_IO
> resource descriptors are ignored to filter out IO port[0xCF8-0xCFF].
> 
> So I plan to make following change to revert to the behavior before
> v3.19:
> 1) make acpi_dev_filter_resource_type() filter descriptors based on
>    descriptor type, and don't check consumer_producer flag anymore.
> 2) use IORESOURCE_IO_FIXED flag to filter out io and fixed_io resource
>    descriptors.
> 3) x86 ACPI pci host bridge driver calls acpi_dev_filter_resource_type()
>    with flag IORESOURCE_IO_FIXED,
> 
> By this way, we could keep acpi_dev_filter_resource_type()
> as a generic interface and could be reused. And the change
> is small too. Any comments?

Sounds good to me.


-- 
I speak only for myself.
Rafael J. Wysocki, Intel Open Source Technology Center.
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