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 10:48:20 -0800
From:	Greg KH <gregkh@...uxfoundation.org>
To:	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
Cc:	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>,
	Yinghai Lu <yinghai@...nel.org>,
	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 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;

Again, no objection to this patch as-is, but should we make it a bit
more "general" and provide a quirk table to make this type of fix easier
for other motherboards?  Shouldn't we also match on a manufacturer field
as well as the board_name?  The kernel provides a very easy to match on
any arbritary set of DMI fields for this kind of problem that we could
use here.

I can make that change if needed.

What are the odds that other boards are going to need a longer delay
time?  Actually, is there a spec saying how long we need to wait?  The
ACPI PCI Hotplug had a value somewhere that the hardware was supposed to
follow, but I don't have access to that ACPI spec anymore to verify
this...

thanks,

greg k-h
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