Message-ID: <2290160.KqiWSgJfFU@vostro.rjw.lan>
Date:	Wed, 29 Apr 2015 16:15:34 +0200
From:	"Rafael J. Wysocki" <rjw@...ysocki.net>
To:	Jiang Liu <jiang.liu@...ux.intel.com>,
	Bjorn Helgaas <bhelgaas@...gle.com>
Cc:	Ingo Molnar <mingo@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	"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 v5] x86/PCI/ACPI: Fix regression caused by commit 63f1789ec716

On Wednesday, April 29, 2015 09:33:16 PM Jiang Liu wrote:
> On 2015/4/29 21:20, Bjorn Helgaas wrote:
> > On Tue, Apr 28, 2015 at 7:40 PM, Rafael J. Wysocki <rjw@...ysocki.net> wrote:
> >> On Monday, April 20, 2015 11:08:58 AM Jiang Liu wrote:
> >>> An IO port or MMIO resource assigned to a PCI host bridge may be
> >>> consumed by the host bridge itself or available to its child
> >>> bus/devices. On x86 and IA64 platforms, all IO port and MMIO
> >>> resources are assumed to be available to child bus/devices
> >>> except one special case:
> >>>     IO port [0xCF8-0xCFF] is consumed by the host bridge itself
> >>>     to access PCI configuration space.
> >>>
> >>> But the ACPI and PCI Firmware specifications haven't provided a method
> >>> to tell whether a resource is consumed by the host bridge itself.
> >>> So before commit 593669c2ac0f ("x86/PCI/ACPI: Use common ACPI resource
> >>> interfaces to simplify implementation"), arch/x86/pci/acpi.c ignored
> >>> all IO port resources defined by acpi_resource_io and
> >>> acpi_resource_fixed_io to filter out IO ports consumed by the host
> >>> bridge itself.
> >>>
> >>> Commit 593669c2ac0f ("x86/PCI/ACPI: Use common ACPI resource interfaces
> >>> to simplify implementation")started accepting all IO port and MMIO
> >>> resources, which caused a regression that IO port resources consumed
> >>> by the host bridge itself became available to its child devices.
> >>>
> >>> Then commit 63f1789ec716 ("x86/PCI/ACPI: Ignore resources consumed by
> >>> host bridge itself") ignored resources consumed by the host bridge
> >>> itself by checking the IORESOURCE_WINDOW flag, which accidently removed
> >>> MMIO resources defined by acpi_resource_memory24, acpi_resource_memory32
> >>> and acpi_resource_fixed_memory32.
> >>>
> >>> So revert to the behavior before v3.19 to fix the regression.
> >>>
> >>> There is also a discussion about ignoring the Producer/Consumer flag on
> >>> IA64 platforms at:
> >>> http://patchwork.ozlabs.org/patch/461633/
> >>>
> >>> Related ACPI table are archived at:
> >>> https://bugzilla.kernel.org/show_bug.cgi?id=94221
> >>>
> >>> Fixes: 63f1789ec716("Ignore resources consumed by host bridge itself")
> >>> Reported-by: Bernhard Thaler <bernhard.thaler@...et.at>
> >>> Signed-off-by: Jiang Liu <jiang.liu@...ux.intel.com>
> >>
> >> Bjorn, Ingo, is anyone looking at this?  We're still having a regression in
> >> this area ...
> > 
> >>> ---
> >>>  arch/x86/pci/acpi.c     |   25 ++++++++++++++++++++++---
> >>>  drivers/acpi/resource.c |    6 +++++-
> >>>  2 files changed, 27 insertions(+), 4 deletions(-)
> >>>
> >>> diff --git a/arch/x86/pci/acpi.c b/arch/x86/pci/acpi.c
> >>> index e4695985f9de..fc2da98985c3 100644
> >>> --- a/arch/x86/pci/acpi.c
> >>> +++ b/arch/x86/pci/acpi.c
> >>> @@ -332,12 +332,32 @@ static void probe_pci_root_info(struct pci_root_info *info,
> >>>  {
> >>>       int ret;
> >>>       struct resource_entry *entry, *tmp;
> >>> +     unsigned long res_flags;
> >>>
> >>>       sprintf(info->name, "PCI Bus %04x:%02x", domain, busnum);
> >>>       info->bridge = device;
> >>> +
> >>> +     /*
> >>> +      * An IO or MMIO resource assigned to PCI host bridge may be consumed
> >>> +      * by the host bridge itself or available to its child bus/devices.
> >>> +      * On x86 and IA64 platforms, all IO and MMIO resources are assumed to
> >>> +      * be available to child bus/devices except one special case:
> >>> +      *      IO port [0xCF8-0xCFF] is consumed by host bridge itself to
> >>> +      *      access PCI configuration space.
> >>> +      *
> >>> +      * Due to lack of specification to define resources consumed by host
> >>> +      * bridge itself, all IO port resources defined by acpi_resource_io
> >>> +      * and acpi_resource_fixed_io are ignored to filter out IO
> >>> +      * port[0xCF8-0xCFF]. Seems this solution works with all BIOSes, though
> >>> +      * it's not perfect.
> > 
> > 1) I think it's misleading to say "the specs haven't provided a
> > method."  As far as I can tell, the Producer/Consumer bit is intended
> > precisely to distinguish resources consumed by a bridge from those
> > forwarded to downstream devices.  It would be more accurate to say
> > "the spec defines a bit, but firmware hasn't used that bit
> > consistently, so we can't rely on it."
> 
> Hi Bjorn,
> 	Thanks for review, I will refine the words as suggested by you.
> 
> > If you want to say "it's not perfect," it would be useful to mention
> > the ways in which it is not perfect.  This code is still a candidate
> > for unification with ia64 and arm64, so we should avoid x86-specific
> > things here as much as possible.
> 
> Yes, I have another pending patch set to consolidate IA64 and x86 code
> for ACPI PCI root.

That's OK, but can we please fix the regression first before doing that
unification?  Like to make life easier for the "stable" people and
whoever wants to backport the fix?


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