Re: [Qemu-devel] Use of flash for x86 BIOS

[Jordan Justen]

On Fri, Mar 22, 2013 at 12:48 PM, Markus Armbruster <address@hidden> wrote:
> Jordan Justen <address@hidden> writes:
>
>> On Thu, Mar 21, 2013 at 12:45 AM, Markus Armbruster <address@hidden> wrote:
>>> x86 maintainers may wish to *switch it off* until it's done fully and
>>> properly, by setting "pc-sysfw" property "rom_only" to 1.
>>
>> This would completely disable the flash support.
>
> Unless the user enables it explicitly with something like "-global
> pc-sysfw.rom_only=0".
>
>>                                                  At the time this
>> feature was added, I think it was well understood that kvm would not
>> support the flash mode, while plain qemu could. If it was not a
>> show-stopper to integrating the feature originally, what has changed?
>
> Nothing changed, and that's the problem.
>
> Merging the feature was okay, I think.  Defaulting it to "on" with TCG
> and "off" with KVM was a mistake, because that made enabling/disabling
> KVM guest-visible (see item 2. below).  The default needs to be the same
> both with and without KVM.  Since the thing still doesn't work with KVM,
> the default needs to be "off".
>
> A possible explanation for making this mistake is that people assumed it
> would soon work with KVM.  That turned out not to be the case.

Given this can be overridden on the command line it does seem
reasonable to disable it by default until KVM support is in place.

Slight off topic, does pc_q35 intend to support SPI flash at some
point? SPI programming is at a different MMIO address from the flash,
so it should be possible to support with qemu/kvm today.

Are there any plans for Q35 to become the default qemu PC machine?

-Jordan