linux-kernel - Re: [Update][PATCH] PCIe / hotplug: Drop pointless ACPI-based "slot detection" check

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Date:	Thu, 11 Jun 2015 13:05:29 -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: [Update][PATCH] PCIe / hotplug: Drop pointless ACPI-based "slot
 detection" check

On 5/21/2015 9:21 PM, Rafael J. Wysocki wrote:
> On Thursday, May 21, 2015 11:11:46 AM Bjorn Helgaas wrote:
>> On Tue, May 19, 2015 at 03:27:58PM +0200, Rafael J. Wysocki wrote:
>>> From: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
>>>
>>> Jarod Wilson reports that the expresscard hotplug setup doesn't work
>>> on HP ZBook G2.  The problem turns out to be the ACPI-based "slot
>>> detection" code called from pciehp_probe() which tries to use some
>>> questionable heuristics based on what ACPI objects are present for
>>> the PCIe port device at hand to figure out whether or not to register
>>> a hotplug slot for that port.
>>>
>>> That code is used if there is at least one PCIe port having an ACPI
>>> device configuration object related to hotplug (such as _EJ0 or _RMV)
>>> and the Thunderbolt port on the affected machine has _RMV.  Of course,
>>> Thunderbolt and PCIe native hotplug need not be mutually exclusive
>>> (as they aren't on the machine in question), so that rule is simply
>>> incorrect.
>>>
>>> Moreover, the ACPI-based "slot detection" check does not add any
>>> value if pciehp_probe() is called at all and the service type of the
>>> device object it has been called for is PCIE_PORT_SERVICE_HP, because
>>> PCIe hotplug services are only registered if the _OSC handshake in
>>> acpi_pci_root_add() allows the kernel to control the PCIe native
>>> hotplug feature.  No more checks need to be carried out to decide
>>> whether or not to register a native PCIe hotlug slot in that case.
>>>
>>> For the above reasons, make pciehp_probe() check if it has been
>>> called for the right service type and drop the pointless ACPI-based
>>> "slot detection" check from it.  Also remove the entire code whose
>>> only user is that check (the entire pciehp_acpi.c file goes away
>>> as a result) and drop function headers related to it from the
>>> internal PCIeHP header file.
>>>
>>> Link: http://marc.info/?t=143163219300002&r=1&w=2
>>> Link: https://bugzilla.kernel.org/show_bug.cgi?id=98581
>>> Reported-by: Jarod Wilson <jarod@...hat.com>
>>> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
>>
>> This is awesome!  Applied to pci/hotplug for v4.2, with Jarod's
>> reviewed/tested-by.
>
> Thanks!

Looks like I didn't test enough. I can't explain WHY, but with this 
applied, now thunderbolt hot unplug of a network adapter goes haywire, 
where prior to the patch, it worked just fine. Still looking into it...

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