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

From: Bjorn Helgaas
Date: Wed Jun 12 2013 - 23:51:14 EST

On Wed, Jun 12, 2013 at 1:41 PM, Yinghai Lu <yinghai@xxxxxxxxxx> wrote:
> On Wed, Jun 12, 2013 at 10:05 AM, Bjorn Helgaas <bhelgaas@xxxxxxxxxx> 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
>>> 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?

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