linux-kernel - Re: [PATCH] pci/hotplug: work-around for missing

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Date:	Mon, 18 May 2015 12:17:23 -0400
From:	Jarod Wilson <jarod@...hat.com>
To:	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	Bjorn Helgaas <bhelgaas@...gle.com>
CC:	linux-kernel@...r.kernel.org, Len Brown <lenb@...nel.org>,
	linux-acpi@...r.kernel.org, linux-pci@...r.kernel.org
Subject: Re: [PATCH] pci/hotplug: work-around for missing _RMV on HP ZBook
 G2

On 5/18/2015 10:33 AM, Jarod Wilson wrote:
> On 5/17/2015 8:26 PM, Rafael J. Wysocki wrote:
>> On Saturday, May 16, 2015 09:41:55 AM Bjorn Helgaas wrote:
>>> On Sat, May 16, 2015 at 09:37:50AM -0500, Bjorn Helgaas wrote:
>>>> Hi Jarod,
>>>>
>>>> On Thu, May 14, 2015 at 03:33:58PM -0400, Jarod Wilson wrote:
>>>>> The HP ZBook 15 and 17 Mobile Workstations, generation 2, up to and
>>>>> including at least BIOS revision 01.07, do not have an ACPI _RMV
>>>>> object
>>>>> associated with their expresscard slots, so acpi-based hotplug-capable
>>>>> slot detection fails. If we fall back to pcie-based detection, the
>>>>> systems
>>>>> work just fine, so this uses dmi matching to do that. With luck, a
>>>>> future
>>>>> BIOS will remedy this (I've let someone at HP know about the problem),
>>>>> but for now, just use this for all existing versions.
> ...
>>>> Oh, my goodness.  I forgot how terrible this path is.  Can anyone
>>>> write a
>>>> simple explanation of how we choose to use acpiphp or pciehp?
>>
>> In theory, that should depend on the _OSC handshake in
>> acpi_pci_root_add().
>>
>> If the firmware doesn't give us control of the PCIe features, we'll
>> not use
>> pciehp (or at least that's the idea).
>>
>> acpiphp is used if pciehp doesn't claim the device, AFAICS.
>
> [    4.013326] acpi PNP0A08:00: _OSC: OS supports [ExtendedConfig ASPM
> ClockPM Segments MSI]
> [    4.015860] acpi PNP0A08:00: _OSC: OS now controls [PCIeHotplug PME
> AER PCIeCapability]
>
> So at a glance, it would appear that pciehp *should* be claiming it,
> right? Something I noted in the bug I filed is that the device ID
> reported there is PNP0A08, and the root_device_id table that associates
> with acpi_pci_root_add() only includes PNP0A03 in it. Is that correct,
> or should 08 also be in there, which might remedy this? (I can test this
> out easily enough).

Nope, makes no difference, seems those are just two different references 
to the same bus, based on a peek at the extracted dsdt:

Name (_HID, EisaId ("PNP0A08") /* PCI Express Bus */)  // _HID: Hardware ID
Name (_CID, EisaId ("PNP0A03") /* PCI Bus */)  // _CID: Compatible ID

-- 
Jarod Wilson
jarod@...hat.com
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