Re: [Qemu-devel] [PATCH v4 6/7] Make the kernel image in the fw_cfg DMA interface bootable

[Laszlo Ersek <lersek@redhat.com>]

On 10/02/15 11:01, Gerd Hoffmann wrote:
>   Hi,
> 
>> A solution that I can see is adding DMA boot capabilities to the
>> linuxboot.S optionrom. I was trying to avoid this, but it looks like
>> not doing so creates lots of problems. It may be better than adding a
>> "nice" shortcut somewhere in QEMU or SeaBIOS.
>>
>> Who uses this optionrom (and will benefit from this change)?
> 
> Any -kernel boot on x86 will use either linuxboot.bin or multiboot.bin.

(Except when your firmware is OVMF -- OVMF has its own LoadLinuxLib. So,
if you decide to extend linuxboot.bin / multiboot.bin with the DMA
capability, that can't regress OVMF by definition, and you certainly
won't hear me complain.)

Thanks
Laszlo

> From a compatibility point of view implementing it in the option rom
> certainly has its advantages.  And as the option roms are shipped with
> and loaded by qemu you don't even have to do runtime detection if that
> simplifies things.  We can just build two versions of the roms and qemu
> can use the one or the other depending on whenever the machine type in
> question has fw_cfg dma enabled or not.
> 
> cheers,
>   Gerd
> 
> 
> 
>