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

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Date:	Tue, 9 Dec 2014 10:26:01 +0800
From:	Wei Yang <weiyang@...ux.vnet.ibm.com>
To:	Yinghai Lu <yinghai@...nel.org>, weiyang@...ux.vnet.ibm.com,
	Gavin Shan <gwshan@...ux.vnet.ibm.com>
Cc:	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Bjorn Helgaas <bhelgaas@...gle.com>,
	Marek Kordík <kordikmarek@...il.com>,
	Alexey Voronkov <zermond@...il.com>,
	"linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] PCI: Clear bridge MEM_64 flag if one child does not
 support it

On Tue, Dec 09, 2014 at 11:11:19AM +1100, Gavin Shan wrote:
>On Mon, Dec 08, 2014 at 03:59:54PM -0800, Yinghai Lu wrote:
>>On Mon, Dec 8, 2014 at 2:56 PM, Benjamin Herrenschmidt
>><benh@...nel.crashing.org> wrote:
>>> 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.
>>
>>the ROM BAR get skipped during the checking.
>>
>>+                       if (i != PCI_ROM_RESOURCE)
>>+                               mem64_mask &= r->flags & IORESOURCE_MEM_64;
>>+               }
>>
>>>
>>> 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...
>>
>>Please check if this patch break your platform. I tried on my setup on
>>x86. and it is still
>>working on 64 bit resource allocation.
>>
>
>I'm going to give it a spin and Richard, could you please apply Yinghai's
>patch to see if your SRIOV code can work properly?
>

Yinghai & Gavin,

I did a quick test on my machine. This patch doesn't affect the MMIO
allocation on out platform, so SRIOV works fine.

I will spend more time to read the patch to get more understanding about the
problem.

>Thanks,
>Gavin

-- 
Richard Yang
Help you, Help me

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