[Qemu-devel] Re: [PATCH 2/3] qemu: make cirrus init value pci spec compliant

[Avi Kivity <avi@redhat.com>]

On 10/08/2009 06:06 PM, Michael S. Tsirkin wrote:
> On Thu, Oct 08, 2009 at 05:29:29PM +0200, Avi Kivity wrote:
>    
>> On 10/08/2009 04:52 PM, Michael S. Tsirkin wrote:
>>      
>>> PCI memory should be disabled at reset, otherwise
>>> we might claim transactions at address 0.
>>> I/O should also be disabled, although for cirrus
>>> it is harmless to enable it as we do not
>>> have I/O bar.
>>>
>>> Note: need bios fix for this patch to work:
>>> currently pc-bios incorrently assumes that it does not
>>> need to enable i/o unless device has i/o bar.
>>>
>>> Signed-off-by: Michael S. Tsirkin<mst@redhat.com>
>>> ---
>>>    hw/cirrus_vga.c |    1 -
>>>    1 files changed, 0 insertions(+), 1 deletions(-)
>>>
>>> diff --git a/hw/cirrus_vga.c b/hw/cirrus_vga.c
>>> index 1feb827..c54ac65 100644
>>> --- a/hw/cirrus_vga.c
>>> +++ b/hw/cirrus_vga.c
>>> @@ -3248,7 +3248,6 @@ static int pci_cirrus_vga_initfn(PCIDevice *dev)
>>>         /* setup PCI */
>>>         pci_config_set_vendor_id(pci_conf, PCI_VENDOR_ID_CIRRUS);
>>>         pci_config_set_device_id(pci_conf, device_id);
>>> -     pci_conf[0x04] = PCI_COMMAND_IOACCESS | PCI_COMMAND_MEMACCESS;
>>>         pci_config_set_class(pci_conf, PCI_CLASS_DISPLAY_VGA);
>>>         pci_conf[PCI_HEADER_TYPE] = PCI_HEADER_TYPE_NORMAL;
>>>
>>>        
>> This needs to be conditional on the machine type.  Old machines must
>> retain this code for live migration to work (we need to live migrate the
>> bios, so we can't assume the bios fix is in during live migration from
>> older qemus).
>>      
> No, if you migrate from older qemu you will be fine as command
> is enabled there on init.
>    

Right.

> Only migration *to* older qemu might create a problem and then only if
> you manage to migrate after pci was reset but before bios set the
> register, which is a small window.
>
> Do we really want to update machine type for this?
>    

No, migration to older qemu is not supported.

-- 
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