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

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Date:	Tue, 19 May 2015 13:36:06 +0200
From:	"Rafael J. Wysocki" <rjw@...ysocki.net>
To:	Jarod Wilson <jarod@...hat.com>
Cc:	Bjorn Helgaas <bhelgaas@...gle.com>, 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 Monday, May 18, 2015 11:06:53 PM Jarod Wilson wrote:
> On 5/18/2015 7:06 PM, Rafael J. Wysocki wrote:
> > On Monday, May 18, 2015 04:45:28 PM Jarod Wilson wrote:
> ...
> >>>>>>> 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
> ...
> >> Ah, I forgot some additional details. pciehp_probe() in
> >> drivers/pci/hotplug/pciehp_core.c fails on the
> >> pciehp_acpi_slot_detection_check() call for the expresscard slot, which
> >> is why the base pciehp doesn't bind. DEVICE_ACPI_HANDLE(&dev->dev) in
> >> the slot detection check is winding up with a NULL acpi device.
> >
> > So IMO the bug is that select_detection_mode() assumes that ACPI should be
> > used as the PCIe hotplug detection method if it has found at least one
> > device that looks like an "ACPI hotplug slot" (Thuderbolt breaks that "logic").
> >
> > To be honest, I'm not sure why we need the pciehp_acpi_slot_detection_check()
> > in pciehp_probe() at all.  It doesn't add any value as far as I can say.
> >
> > If pciehp_probe() is called at all, we have registered a PCIe port service
> > and if this is a "hotplug" service, we wouldn't have registered it if the
> > _OSC handshake had not given us contol over native hotplug.
> >
> > So I wonder if the patch below makes any difference.
> 
> Yeah, that also works, for the most part. You still get spew from 
> pciehp_acpi_slot_detection_init() saying "Using ACPI for slot 
> detection.", but in re-reading pciehp_acpi.c in its entirety... I can't 
> see anything productive that it actually does. I'm of the mind that the 
> entire file should just be nuked, the path from pciehp_core.c that your 
> patch alters was the only one that called 
> pciehp_acpi_slot_detection_check(), and everything else is basically the 
> dummy probe and fluff, nothing meaningful actually happens.

Right, all that is horrible horrible garbage.

> I can whip up a follow-up patch that neuters that file entirely in the morning.

Well, let me have that pleasure. :-)

Anyway, code that is only used in one place should be dropped along with its
only user.

> At the very least, the "Using ACPI" bit needs to be beaten into submission, 
> since its not going to be accurate.

An updated patch will follow this message.


-- 
I speak only for myself.
Rafael J. Wysocki, Intel Open Source Technology Center.
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