linux-kernel - Re: [PATCH] PCI: Remove not needed check in disable aspm link

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Message-ID: <CAErSpo7=a-wX6BLbm_O1nUMMrQHOgtSm3xZHKuRqaz8rnKSbRA@mail.gmail.com>
Date:	Wed, 12 Jun 2013 11:05:04 -0600
From:	Bjorn Helgaas <bhelgaas@...gle.com>
To:	Yinghai Lu <yinghai@...nel.org>
Cc:	Jiang Liu <jiang.liu@...wei.com>,
	Roman Yepishev <roman.yepishev@...il.com>,
	"Rafael J. Wysocki" <rjw@...k.pl>,
	"linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
	"linux-acpi@...r.kernel.org" <linux-acpi@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Taku Izumi <izumi.taku@...fujitsu.com>,
	Kenji Kaneshige <kaneshige.kenji@...fujitsu.com>,
	Matthew Garrett <matthew.garrett@...ula.com>,
	"e1000-devel@...ts.sourceforge.net" 
	<e1000-devel@...ts.sourceforge.net>
Subject: Re: [PATCH] PCI: Remove not needed check in disable aspm link

On Wed, Jun 12, 2013 at 12:20 AM, Yinghai Lu <yinghai@...nel.org> wrote:
> On Tue, Apr 2, 2013 at 1:10 PM, Bjorn Helgaas <bhelgaas@...gle.com> wrote:
>> On Mon, Apr 1, 2013 at 6:03 PM, Yinghai Lu <yinghai@...nel.org> wrote:
>>>> commit 96e5d01cd536458435ef0678d9fa3dc542afb41f
>>>> 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.
>>>>
>>>>     Conflicts:
>>>>         drivers/acpi/pci_root.c
>>>>
>>>>     Reference: https://bugzilla.kernel.org/show_bug.cgi?id=55211
>>>>     Signed-off-by: Bjorn Helgaas <bhelgaas@...gle.com>
>>>
>>> Acked-by: Yinghai Lu <yinghai@...nel.org>
>>>
>>> stable need this reverting too.
>>
>> I updated the changelog and added this to my for-linus branch, headed for v3.9.
>
> We may need to revert this reverting for 3.10.
>
> Today noticed that acpiphp jump in before pciehp on one setup.
>
> current code from acpi_pci_root_add we have
>   1. pci_acpi_scan_root
>          ==> pci devices enumeration and bus scanning.
>              ==> pci_alloc_child_bus
>                  ==> pcibios_add_bus
>                      ==> acpi_pci_add_bus
>                          ==> acpiphp_enumerate_slots
>                              ==> ...==> register_slot
>                                   ==> device_is_managed_by_native_pciehp
>                                         ==> check osc_set with
> OSC_PCI_EXPRESS_NATIVE_HP_CONTROL
>    2. _OSC set request
>
> so we always have acpiphp hotplug slot registered at first.
>
> so either we need to
> A. revert reverting about _OSC
> B. move pcibios_add_bus down to pci_bus_add_devices()
>     as acpiphp and apci pci slot driver are some kind of drivers for pci_bus
> C. A+B

It doesn't surprise me at all that there are problems in the _OSC code
and the acpiphp/pciehp interaction.  That whole area is a complete
disaster.  It'd really be nice if somebody stepped up and reworked it
so it makes sense.

But this report is useless to me.  I don't have time to work out what
the problem is and how it affects users and come up with a fix.

My advice is to simplify the path first, and worry about fixing the
bug afterwards.  We've already done several iterations of fiddling
with things, and I think all we're doing is playing "whack-a-mole" and
pushing the bugs around from one place to another.

Bjorn
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