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Date: Fri, 09 Oct 2009 08:40:58 +0200
From: Avi Kivity <avi@redhat.com>
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Subject: Re: [Qemu-devel] [PATCHv2] seabios: enable io/memory	unconditionally
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To: Kevin O'Connor <kevin@koconnor.net>
Cc: Anthony Liguori <aliguori@us.ibm.com>, "qemu-devel@nongnu.org" <qemu-devel@nongnu.org>, kvm-devel <kvm@vger.kernel.org>, "Michael S. Tsirkin" <mst@redhat.com>

On 10/09/2009 04:29 AM, Kevin O'Connor wrote:
> Hi Michael,
>
> On Thu, Oct 08, 2009 at 05:53:46PM +0200, Michael S. Tsirkin wrote:
>    
>> VGA adapters need to claim memory and i/o
>> transactions even if they do not have any
>> i/o or memory bars. E.g. PCI spec, page 297,
>> gives an example of such a device:
>>
>>      Programming interface 0000 0000b
>>      VGA-compatible controller. Memory
>>      addresses 0A 0000h through 0B
>>      FFFFh. I/O addresses 3B0h to 3BBh
>>      and 3C0h to 3DFh and all aliases of
>>      these addresses.
>>
>> While we could check for these devices and special-case them, it is
>> easier to fix this by enabling i/o and memory space unconditionally:
>> devices that do not support it will just ignore this setting.
>>      
> This doesn't sound correct to me - I would think the vga option rom
> should enable the memory and io bars.  I don't have enough knowledge
> to say for sure though - can someone else with knowledge in this area
> confirm this approach?
>
>    

The vga option rom is often itself in a BAR, so it cannot enable memory.

-- 
Do not meddle in the internals of kernels, for they are subtle and quick to panic.