Re: [PATCH v3 2/2] hw/arm: Add the romfile compatatibility

["Daniel P. Berrangé" <berrange@redhat.com>]

On Mon, Jun 09, 2025 at 09:48:36AM +0100, Peter Maydell wrote:
> On Mon, 9 Jun 2025 at 08:34, Shaoqin Huang <shahuang@redhat.com> wrote:
> >
> > On arm64, it doesn't use the vgabios-ramfb.bin, so set the property
> > "use-legacy-x86-rom" to false, thus the ramfb won't load the
> > vgabios-ramfb.bin.
> >
> > This can mitigate the problem that on release version the qemu can't
> > find the vgabios-ramfb.bin if it use the ramfb.
> >
> > Signed-off-by: Shaoqin Huang <shahuang@redhat.com>
> > ---
> >  hw/arm/virt.c | 3 +++
> >  1 file changed, 3 insertions(+)
> >
> > diff --git a/hw/arm/virt.c b/hw/arm/virt.c
> > index a96452f17a..5f94f7a2ca 100644
> > --- a/hw/arm/virt.c
> > +++ b/hw/arm/virt.c
> > @@ -38,6 +38,7 @@
> >  #include "hw/arm/primecell.h"
> >  #include "hw/arm/virt.h"
> >  #include "hw/block/flash.h"
> > +#include "hw/vfio/pci.h"
> >  #include "hw/vfio/vfio-calxeda-xgmac.h"
> >  #include "hw/vfio/vfio-amd-xgbe.h"
> >  #include "hw/display/ramfb.h"
> > @@ -90,6 +91,8 @@
> >
> >  static GlobalProperty arm_virt_compat[] = {
> >      { TYPE_VIRTIO_IOMMU_PCI, "aw-bits", "48" },
> > +    { TYPE_RAMFB_DEVICE, "use-legacy-x86-rom", "false" },
> > +    { TYPE_VFIO_PCI, "use-legacy-x86-rom", "false" },
> 
> I think we should find a way to make this default to "false"
> and only be set "true" for x86. Otherwise every single non-x86
> board that ever adds support for ramfb and virtio will have
> to add these two lines, which is a source of future bugs.
> (Whereas if you forget to mark a new x86 board as needing
> the legacy rom you'll find out about it pretty quickly.)

Yes, going forward we this to default to true only on x86.

For non-x86, historical versioned machine types will need
likely it set to true, in order to avoid the memory layout
being changed IIUC.


With regards,
Daniel
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