linux-kernel - Re: [PATCH 3/3] PCI Hotplug: workaround for Thunderbolt on Intel DZ77RE-75K motherboard

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Date:	Thu, 13 Dec 2012 12:25:53 -0800
From:	Yinghai Lu <yinghai@...nel.org>
To:	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Greg KH <gregkh@...uxfoundation.org>,
	Miles J Penner <miles.j.penner@...el.com>,
	John Ronciak <john.ronciak@...el.com>,
	Mika Westerberg <mika.westerberg@...ux.intel.com>,
	Tushar N Dave <tushar.n.dave@...el.com>,
	"Kirill A. Shutemov" <kirill@...temov.name>,
	Bjorn Helgaas <bhelgaas@...gle.com>,
	Jesse Barnes <jbarnes@...tuousgeek.org>,
	Amos Kong <kongjianjun@...il.com>,
	"Rafael J. Wysocki" <rjw@...k.pl>, linux-pci@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 3/3] PCI Hotplug: workaround for Thunderbolt on Intel
 DZ77RE-75K motherboard

On Thu, Dec 13, 2012 at 12:08 PM, Kirill A. Shutemov
<kirill.shutemov@...ux.intel.com> wrote:
> On Thu, Dec 13, 2012 at 10:48:20AM -0800, Greg KH wrote:
>> On Thu, Dec 13, 2012 at 05:31:48PM +0200, Kirill A. Shutemov wrote:
>> > From: "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
>> >
>> > BIOS on Intel DZ77RE-75K motherboard notifies OS about Thunderbolt
>> > hotplug before devices behind Thunderbolt are ready to be enumerated.
>> >
>> > Let's delay enumeration by 2 seconds.
>> >
>> > Signed-off-by: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>
>> > ---
>> >  drivers/pci/hotplug/acpiphp_glue.c |   16 +++++++++++++++-
>> >  1 file changed, 15 insertions(+), 1 deletion(-)
>> >
>> > diff --git a/drivers/pci/hotplug/acpiphp_glue.c b/drivers/pci/hotplug/acpiphp_glue.c
>> > index 1a2b3ca..165987a 100644
>> > --- a/drivers/pci/hotplug/acpiphp_glue.c
>> > +++ b/drivers/pci/hotplug/acpiphp_glue.c
>> > @@ -49,6 +49,7 @@
>> >  #include <linux/mutex.h>
>> >  #include <linux/slab.h>
>> >  #include <linux/acpi.h>
>> > +#include <linux/dmi.h>
>> >
>> >  #include "../pci.h"
>> >  #include "acpiphp.h"
>> > @@ -1327,6 +1328,19 @@ out:
>> >  static void handle_hotplug_event_bridge(acpi_handle handle, u32 type,
>> >                                     void *context)
>> >  {
>> > +   unsigned long delay = 0;
>> > +   const char *board_name;
>> > +
>> > +   board_name = dmi_get_system_info(DMI_BOARD_NAME);
>> > +   /*
>> > +    * BIOS on Intel DZ77RE-75K motherboard notifies OS about Thunderbolt
>> > +    * hotplug before devices behind Thunderbolt are ready to be
>> > +    * enumerated.
>> > +    * Let's delay enumeration by 2 seconds.
>> > +    */
>> > +   if (board_name && !strcmp(board_name, "DZ77RE-75K"))
>> > +           delay = 2 * HZ;
>>

Linus will not be happy with those kind of delay.

is there any way for kernel to retry before device is declared not there.

pcie hotplug spec: need to retry several times in 1000ms before
delcaring the devices is not present.

http://git.kernel.org/?p=linux/kernel/git/torvalds/linux.git;a=commitdiff;h=2f5d8e4ff947ad6673397083b48719cd6c59cd61
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