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Re: [Qemu-ppc] [Qemu-devel] [PATCH v2] pci: allow 0 address for PCI IO/M
From: |
Peter Maydell |
Subject: |
Re: [Qemu-ppc] [Qemu-devel] [PATCH v2] pci: allow 0 address for PCI IO/MEM regions |
Date: |
Thu, 23 Jul 2015 22:00:30 +0100 |
On 23 July 2015 at 21:46, Benjamin Herrenschmidt
<address@hidden> wrote:
> On Thu, 2015-07-23 at 20:24 +0200, Laurent Vivier wrote:
>> From: Michael Roth <address@hidden>
>>
>> Some kernels program a 0 address for io regions. PCI 3.0 spec
>> section 6.2.5.1 doesn't seem to disallow this.
>>
>> Signed-off-by: Michael Roth <address@hidden>
>> [lvivier: add pci_allow_0_addr in MachineClass to conditionally
>> allow addr 0 for pseries, as this can break other architectures]
>> Signed-off-by: Laurent Vivier <address@hidden>
>> ---
>
> Why would it break other architectures ? The PCI bus will forward
> address 0 just fine and some devices will decode it just fine too,
> regardless of the architecture they are put on. I don't see why
> having BARs capable of decoding it would break anything...
Discussion from last time around:
http://lists.gnu.org/archive/html/qemu-devel/2015-01/msg01358.html
suggests that it's a workaround for our PC model being buggy
and putting 0-address BARs over the top of some other system
device rather than underneath them...
(Also, none of our PCI device models actually try to do
the "BAR at zero means I won't respond" behaviour, which
presumably they might do in real life.)
-- PMM
- Re: [Qemu-ppc] [PATCH|RFC 1/1] pci: allow 0 address for PCI IO/MEM regions, (continued)
Re: [Qemu-ppc] [PATCH|RFC 1/1] pci: allow 0 address for PCI IO/MEM regions, Michael S. Tsirkin, 2015/07/23
[Qemu-ppc] [PATCH v2] pci: allow 0 address for PCI IO/MEM regions, Laurent Vivier, 2015/07/23
Re: [Qemu-ppc] [PATCH v2] pci: allow 0 address for PCI IO/MEM regions, Benjamin Herrenschmidt, 2015/07/23
- Re: [Qemu-ppc] [Qemu-devel] [PATCH v2] pci: allow 0 address for PCI IO/MEM regions,
Peter Maydell <=
- Re: [Qemu-ppc] [Qemu-devel] [PATCH v2] pci: allow 0 address for PCI IO/MEM regions, Michael S. Tsirkin, 2015/07/23
- Re: [Qemu-ppc] [Qemu-devel] [PATCH v2] pci: allow 0 address for PCI IO/MEM regions, Peter Maydell, 2015/07/23
- Re: [Qemu-ppc] [Qemu-devel] [PATCH v2] pci: allow 0 address for PCI IO/MEM regions, Peter Maydell, 2015/07/23
- Re: [Qemu-ppc] [Qemu-devel] [PATCH v2] pci: allow 0 address for PCI IO/MEM regions, Michael Roth, 2015/07/23
- Re: [Qemu-ppc] [Qemu-devel] [PATCH v2] pci: allow 0 address for PCI IO/MEM regions, Michael Roth, 2015/07/23
- Re: [Qemu-ppc] [Qemu-devel] [PATCH v2] pci: allow 0 address for PCI IO/MEM regions, Peter Maydell, 2015/07/24
- Re: [Qemu-ppc] [Qemu-devel] [PATCH v2] pci: allow 0 address for PCI IO/MEM regions, Laurent Vivier, 2015/07/24
Re: [Qemu-ppc] [Qemu-devel] [PATCH v2] pci: allow 0 address for PCI IO/MEM regions, Benjamin Herrenschmidt, 2015/07/23
Re: [Qemu-ppc] [Qemu-devel] [PATCH v2] pci: allow 0 address for PCI IO/MEM regions, Michael S. Tsirkin, 2015/07/23
[Qemu-ppc] [PATCH v3] pci: allow 0 address for PCI IO/MEM regions, Laurent Vivier, 2015/07/24