Re: [Qemu-devel] [PATCHv2] seabios: enable io/memory unconditionally

[Avi Kivity]

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.