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

[Avi Kivity]

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<address@hidden>
> > > ---
> > >    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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