linux-kernel - Re: [PATCH 1/6] PCI: acpiphp: do not check for SLOT_ENABLED in enable

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Message-Id: <20130628095138.D5B7BE0090@blue.fi.intel.com>
Date:	Fri, 28 Jun 2013 12:51:38 +0300 (EEST)
From:	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
To:	Bjorn Helgaas <bhelgaas@...gle.com>
Cc:	Mika Westerberg <mika.westerberg@...ux.intel.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	"Rafael J. Wysocki" <rafael.j.wysocki@...el.com>,
	Jesse Barnes <jbarnes@...tuousgeek.org>,
	Yinghai Lu <yinghai@...nel.org>,
	"Ronciak, John" <john.ronciak@...el.com>,
	"Penner, Miles J" <miles.j.penner@...el.com>,
	Bruce Allan <bruce.w.allan@...el.com>,
	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
	Heikki Krogerus <heikki.krogerus@...ux.intel.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
	"x86@...nel.org" <x86@...nel.org>
Subject: Re: [PATCH 1/6] PCI: acpiphp: do not check for SLOT_ENABLED in
 enable_device()

Bjorn Helgaas wrote:
> On Tue, Jun 25, 2013 at 10:22 AM, Mika Westerberg
> <mika.westerberg@...ux.intel.com> wrote:
> > From: "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
> >
> > With Thunderbolt you can chain devices: connect a new devices to plugged
> > one. In this case the slot is already enabled, but we still want to look
> > for new devices behind it.
> >
> > We're going to reuse enable_device() for rescan for new devices on the
> > enabled slot. Let's push the check up by stack.
> >
> > Signed-off-by: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>
> > Signed-off-by: Mika Westerberg <mika.westerberg@...ux.intel.com>
> > ---
> >  drivers/pci/hotplug/acpiphp_glue.c | 5 ++---
> >  1 file changed, 2 insertions(+), 3 deletions(-)
> >
> > diff --git a/drivers/pci/hotplug/acpiphp_glue.c b/drivers/pci/hotplug/acpiphp_glue.c
> > index 59df857..b983e29 100644
> > --- a/drivers/pci/hotplug/acpiphp_glue.c
> > +++ b/drivers/pci/hotplug/acpiphp_glue.c
> > @@ -688,9 +688,6 @@ static int __ref enable_device(struct acpiphp_slot *slot)
> >         int num, max, pass;
> >         LIST_HEAD(add_list);
> >
> > -       if (slot->flags & SLOT_ENABLED)
> > -               goto err_exit;
> > -
> >         list_for_each_entry(func, &slot->funcs, sibling)
> >                 acpiphp_bus_add(func);
> >
> > @@ -1242,6 +1239,8 @@ int acpiphp_enable_slot(struct acpiphp_slot *slot)
> >                 goto err_exit;
> >
> >         if (get_slot_status(slot) == ACPI_STA_ALL) {
> > +               if (slot->flags & SLOT_ENABLED)
> > +                       goto err_exit;
> 
> Why do we check for SLOT_ENABLED at all?  I think we're handling a Bus
> Check notification, which means "re-enumerate on the device tree
> starting from the notification point."  It doesn't say anything about
> skipping the re-enumeration if we find a device that's already
> enabled.
> 
> It seems like we ought to just re-enumerate all the way down in case a
> device was added farther down in the tree (which is what it sounds
> like Thunderbolt is doing).

Currently (with patchset applied), we have two users of
acpiphp_enable_slot():

- /sys/bus/pci/slots/*/power
- ACPI_NOTIFY_BUS_CHECK in _handle_hotplug_event_func().

Both are not related to Thunderbolt.

Although, I think remove the check is good idea, I prefer to keep it
separate from Thunderbolt enabling patchset, since it will change sysfs
ABI a bit and can potentially affect othe ACPI PCI hotplug
implementations.

-- 
 Kirill A. Shutemov
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