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Re: [Qemu-ppc] [Qemu-devel] [PATCH 0/1] pci: allow 0 address for PCI IO/

From: Claudio Fontana
Subject: Re: [Qemu-ppc] [Qemu-devel] [PATCH 0/1] pci: allow 0 address for PCI IO/MEM regions
Date: Tue, 13 Jan 2015 10:05:53 +0100
User-agent: Mozilla/5.0 (Windows NT 6.1; rv:24.0) Gecko/20100101 Thunderbird/24.0.1

On 13.01.2015 06:46, David Gibson wrote:
> On Mon, Jan 12, 2015 at 07:24:06AM -0600, Michael Roth wrote:
>> Quoting Michael Roth (2014-12-23 13:33:35)
>>> This patch enables the programming of address 0 for IO/MMIO BARs for
>>> PCI devices.
>>> It was originally included as part of a series implementing PCI
>>> hotplug for pseries guests, where it is needed due to the fact
>>> that pseries guests access IO space via MMIO, and that IO
>>> space is dedicated to PCI devices, with RTAS calls being used in
>>> place of common/legacy IO ports such as config-data/config-address.
>>> Thus, the entire range is unhindered by legacy IO ports, and
>>> pseries guest kernels may attempt to program an IO BAR to address 0
>>> as a result.
>>> This has led to a conflict with the existing PCI config space
>>> emulation code, where it has been assumed that 0 address are always
>>> invalid.
>>> Some background from discussions can be viewed here:
>>>   https://lists.nongnu.org/archive/html/qemu-devel/2014-08/msg03063.html
>>> The general summary from that discussion seems to be that 0-addresses are
>>> not (at least, are no longer) prohibited by current versions of the PCI
>>> spec, and that the same should apply for MMIO addresses (where allowing
>>> 0-addresses are also needed for some ARM-based PCI controllers).
>>> This patch includes support for 0-address MMIO BARs based on that
>>> discussion.
>>> One still-lingering concern is whether this change will impact
>>> compatibility with guests where 0-addresses are invalid. There was
>>> some discussion on whether this issue could be addressed using
>>> memory region priorities, but I think that's still an open question
>>> that we can hopefully address here.
>> Ping
> Sorry, I just got back from vacation.
> It looks same to me.
> Reviewed-by: David Gibson <address@hidden>

Can you guys take a look also at this:


I really think we should give diagnostics under PCI_DEBUG when trying to set 
new BAR addresses fails for any reason.



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