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Message-ID: <51CB5D84.4080709@zytor.com>
Date:	Wed, 26 Jun 2013 14:30:44 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Bjorn Helgaas <bhelgaas@...gle.com>
CC:	Darren Hart <dvhart@...ux.intel.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Peter P Waskiewicz Jr <peter.p.waskiewicz.jr@...el.com>,
	Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
	danders@...cuitco.com, vishal.l.verma@...el.com,
	"linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>
Subject: Re: [PATCH 7/8] pci: Add CircuitCo VENDOR ID and MinnowBoard DEVICE
 ID
On 06/26/2013 12:37 PM, Bjorn Helgaas wrote:
> 
> Yeah, that's what I was thinking.
> 
> But Peter's comment makes more sense to me now.  The spec refers to
> that config register as "Subsystem ID," not "Subsystem Device ID," but
> I was confused because most existing usage treats it as a device ID.
> For example, the field in struct pci_device_id is named "subdevice,"
> and all the existing #defines in pci_ids.h are of the form
> PCI_SUBDEVICE_ID_*.
> 
> Device IDs are pretty specific identifiers, so I was thinking that a
> "sub-device ID" would be even more specific.  Then it would make no
> sense to have a "sub-device ID" that was as generic as "MINNOWBOARD."
> But the register is actually *not* a "sub-device ID," and I can see
> that using the same Subsystem ID for all the devices on a board might
> make sense.
> 
Subsystem IDs is basically a board ID in the traditional PC view, but
they didn't call it that because it would have been confusing in other,
nontraditional configurations.
Microsoft has a "best practices" document, which may end up becoming
basis for a future PCI-SIG document clarifying the standard:
http://msdn.microsoft.com/en-us/library/windows/hardware/gg463287.aspx
	-hpa
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