Re: [Qemu-devel] Re: [PATCH 0/22] Refactor machine support

[Blue Swirl]

On Wed, Jun 9, 2010 at 2:30 PM, Paul Brook <address@hidden> wrote:
>> >> Because at some point the base tree will have to be written in C.
>> >
>> > No. You can start with a completely empty machine.
>> > We don't/shouldn't need any machine specific C code.
>>
>> I think you're missing the argument.  I should be possible to create a
>> machine entirely from a FDT or via -device options.
>>
>> However, to continue to support the interfaces that we support today, it
>> will be necessary to have C code that manipulates a base device tree.
>>
>> When a user specifies '-M pc -hda foo.img'  verses '-M versatilepb -hda
>> foo.img', the equivalent are two very different operations on a device
>> tree.  The former adds an ide disk to the default controller and the
>> later potentially creates a new scsi bus and then adds a disk to a
>> specific bus.
>
> AFAICS the current commandline options only result in simple addition of
> devices. They might add slightly different devices in slightly different
> places, but that's easy to accommodate by having the machine define a few
> standard device/bus IDs.
>
> IMO it's even more lame if -hda shops working when you supply a device tree.

The tree supplied by the user should label a bus node with a property
'QEMU,hda'. The C version (called by the board) would be something
like setprop("/i440fx/pci.0/ide.0", "QEMU,hda"). QEMU should search
the device tree for such labels at startup.