Re: [Qemu-devel] [PATCH 3/3] PPC PReP: can run without bios image

[Alexander Graf]

On 04.04.2013, at 13:53, Andreas Färber wrote:

> Am 04.04.2013 11:57, schrieb Artyom Tarasenko:
>> On Thu, Apr 4, 2013 at 11:50 AM, Alexander Graf <address@hidden> wrote:
>>> 
>>> On 04.04.2013, at 11:46, Artyom Tarasenko wrote:
>>> 
>>>> On Thu, Apr 4, 2013 at 10:37 AM, Fabien Chouteau <address@hidden> wrote:
>>>>> 
>>>>> On 04/03/2013 06:59 PM, Alexander Graf wrote:
>>>>>> 
>>>>>> On 03.04.2013, at 18:40, Fabien Chouteau wrote:
>>>>>> 
>>>>>>> If we use an ELF kernel there's no need for bios. '-bios -' means no
>>>>>>> bios.
>>>>>> 
>>>>>> This sounds like you're actually looking for a way to load an ELF blob
>>>>>> as bios using -bios, not a kernel, no?
>>>>>> 
>>>>> 
>>>>> No, we load the kernel with -kernel, that's what the first patch does.
>>>>> But the board is implemented in such way that you can't start without a
>>>>> bios. If the -bios switch is not present, then the board uses the
>>>>> default bios. This patch allows to start without a bios:
>>>>> 
>>>>> -kernel <PROGRAM> -bios -
>>>> 
>>>> Regardless of the firmware vs. kernel discussion, I think the syntax
>>>> may be improved. Under *nix '-' is commonly used for stdin. Would it
>>>> be possible to specify /dev/null (under *NIX) or NUL (in the
>>>> MS-World)? I think it would make the syntax more explicit.
>>> 
>>> I'd be inclined to say that running -kernel without -bios is simply bogus 
>>> and shouldn't ever happen.
>> 
>> QEMU does it at least in one other architectures though: leon3_generic.
> 
> Let's rather say: Fabien did it in leon3, too. ;)
> 
> Alex, isn't ARM running without -bios? Instead of a firmware blob it has
> some hardcoded firmware'ish instructions in the loader code.

That still means it runs a firmware. It just generates it on the fly instead of 
loading it from -bios :). X86 used to do the same.

> For PReP, Fabien has not stated what his use case actually is (in
> particular which hardware?), so it's hard for me to comment on what the
> hardware actually does and I thus won't accept random changes just
> because they happen to be in Leon3 code. There's nothing conceptually
> wrong with loading ELF code so I'm positive we will find a solution to
> accommodate all use cases in some way. :)

I think it makes a lot of sense to support loading -kernel as an ELF binary. I 
don't think it's a good idea to allow -kernel without any BIOS. We do that on 
the e500 machines and so far it's mostly hurt us.


Alex