linux-kernel - Re: [PATCH] x86, pci: Add quirk for unsizeable Broadwell EP bar

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Message-ID: <20160204185442.GA4875@tassilo.jf.intel.com>
Date:	Thu, 4 Feb 2016 10:54:42 -0800
From:	Andi Kleen <ak@...ux.intel.com>
To:	Bjorn Helgaas <helgaas@...nel.org>
Cc:	Andi Kleen <andi@...stfloor.org>, bhelgaas@...gle.com,
	linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org,
	x86@...nel.org
Subject: Re: [PATCH] x86, pci: Add quirk for unsizeable Broadwell EP bar

> It sounds like these devices have some device-specific register where
> BAR 0 is supposed to be?  Setting IORESOURCE_PCI_FIXED doesn't seem
> like the right solution to me.  Even if we set that, the core still

There is no actually functional register on these locations that has any side
effects.

> believes this resource corresponds to some address space consumed by
> the device.  I think we will still try to size the BAR and decode its
> type.  I think it will still show up via lspci.  That's all
> meaningless.

But would actually anything use it?

> How do you deal with this on Windows?
> 
> I think you need to replace the config accessor with a special one
> that knows that this register is not a BAR, and they can return zero.
> Or maybe the accessor should hide these devices completely, i.e.,
> return 0xffffffff for the vendor/device ID.  Or maybe you even have a
> switch the BIOS can use to hide them from the OS.

In some cases we need the devices.

-Andi