linux-kernel - Re: [PATCH] PCI: Clear bridge MEM_64 flag if one child does not support it

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Date:	Tue, 09 Dec 2014 09:56:12 +1100
From:	Benjamin Herrenschmidt <benh@...nel.crashing.org>
To:	Yinghai Lu <yinghai@...nel.org>
Cc:	Bjorn Helgaas <bhelgaas@...gle.com>,
	Gavin Shan <gwshan@...ux.vnet.ibm.com>,
	Marek Kordík <kordikmarek@...il.com>,
	zermond@...il.com, linux-pci@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] PCI: Clear bridge MEM_64 flag if one child does not
 support it

On Mon, 2014-12-08 at 13:52 -0800, Yinghai Lu wrote:
> 2. or scan the children resource other than ROM to clear bridge MEM_64
>    for mmio pref.
> 
> The patch is using second way so will keep child mmio pref into bridge
> mmio pref range.

That means that having a single ROM BAR that is 32-bit and prefetchable
will downgrade the entire window to 32-bit ? That's not going to work
either.

I have GPUs with 16G BARs for example... suddenly they don't fit
anaymore because we downgraded the window to 32 bit because somewhere
there's a 32-bit pref resource ?

That will break more than it fixes...

Ben.


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