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

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Date:	Wed, 12 Jun 2013 21:50:45 -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>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Subject: Re: [PATCH] PCI: Remove not needed check in disable aspm link

On Wed, Jun 12, 2013 at 1:41 PM, Yinghai Lu <yinghai@...nel.org> wrote:
> On Wed, Jun 12, 2013 at 10:05 AM, Bjorn Helgaas <bhelgaas@...gle.com> wrote:
>>> 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.
>
> effects: without fix the problem, user can not use pcie native hotplug
> if their system's firmware support acpihp and pciehp.
> And make it worse, that acpiphp have to be built-in, so they have no
> way to blacklist acpiphp in config.
>
>>
>> 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.
>
> We need to address regression at first.
> my suggestion is : revert the reverting and apply my -v3 version that will fix
> regression that Roman Yepishev met.
>
> please check attached two patches, hope it could save your some time.

OK, you're right.  It's not reasonable to do anything more than a
minimal fix when we're at -rc5.

Sigh.  I'll spend tomorrow trying to understand your patches and write
changelogs for you.

I think you're saying that in systems that support both acpiphp and
pciehp, we should be using pciehp, but we currently use acpiphp.  If
so, that's certainly a bug.  How serious is it?  Is it a disaster if
we use acpiphp until we can resolve this cleanly?  Are there a lot of
systems that claim to support acpiphp but it doesn't actually work?

Bjorn
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