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

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Message-ID: <555B2F98.4050906@redhat.com>
Date:	Tue, 19 May 2015 08:42:00 -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] PCIe / hotplug: Drop pointless ACPI-based "slot detection"
 check

On 5/19/2015 7:43 AM, 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>
> ---
>
> Bjorn, that's -stable material I think.  It should be applicable at least
> since commit 5ba113f7c4fb (PCI: acpiphp: Handle PCIe ports without native
> hotplug capability) that was shipped in 3.10.
>
> Thanks!

I believe you also want to rip the pciehp_acpi.o hunk out of 
drivers/pci/hotplug/Makefile, but I made more or less the exact same 
changes here, and am about to give them a spin on the ZBook 17.

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