Re: [Qemu-devel] [PATCH] turn firmware image filename into a machine option

[Alexey Kardashevskiy]

On 10/01/2013 11:46 PM, Andreas Färber wrote:
> Am 01.10.2013 15:41, schrieb Gerd Hoffmann:
>> On Di, 2013-10-01 at 14:20 +0200, Andreas Färber wrote:
>>> Hi,
>>>
>>> Am 01.10.2013 14:16, schrieb Gerd Hoffmann:
>>>>> -bios we're stuck with because it's a legacy
>>>>> option,
>>>>
>>>> What is legacy about it?
>>>>
>>>> Well, the x86-centric name of course.  Thats why the machine option is
>>>> named 'firmware' instead.
>>>>
>>>> It also doesn't use QemuOpts, which is fixed by this patch.
>>>>
>>>> Anything else?
>>>
>>> The basic assumption that there is only one piece of firmware. Just like
>>> -bios, -machine firmware= will allow only one entry. sPAPR has two.
>>
>> --verbose please.  What they are needed for?
> 
> SLOF and RTAS. SLOF is the firmware, and RTAS is requested by the OS
> through OpenFirmware client interface.
> 
> It is not device-specific, it is more or less part of the firmware but
> copied to RAM. I'll let Alex or Alexey comment in more details.

SLOF is what is loaded from the very beginning, it configures PCI, cooks
the device tree and boots the guest system (directly or via yaboot/grub,
from disk, network or ram). Normal firmware, as usual. It knows all the
details about the machine so the guest system (linux) does not need to know
details about PCI host bus adapter or anything like this.

RTAS is an agent which always lives in RAM when the guest system (linux,
aix) is up and running. It is a light-weight version of SLOF which is left
in RAM by SLOF and can do board/machine specific tasks such as PCI config
space access or PCI hotplug - something what SLOF already knows about and
something what the guest does not want to know about in details. This came
from IBM pHyp (traditional server PPC64 hypervisor) and it is quite a big
firmware. In the case of KVM, it is very small stub which simply passes
requests to QEMU which does the rest. But it is still a separate binary
image even in the current QEMU.

May be some day it will become bigger as from time to time the community
wants things to be done in a certain way which would mean extending rtas,
however we (powerpc-server folks) want to hope it won't happen ever :)

Adding Ben in copy, he might have something to add.


-- 
Alexey