[Qemu-devel] Re: [PATCHv4 15/15] Pass boot device list to firmware.

[Gleb Natapov]

On Thu, Nov 18, 2010 at 01:38:31PM +0200, Michael S. Tsirkin wrote:
> On Thu, Nov 18, 2010 at 12:18:27PM +0200, Gleb Natapov wrote:
> > On Wed, Nov 17, 2010 at 09:54:27PM +0000, Blue Swirl wrote:
> > > 2010/11/16 Gleb Natapov <address@hidden>:
> > > > On Tue, Nov 16, 2010 at 06:30:19PM +0000, Blue Swirl wrote:
> > > >> >> Perhaps the FW path should use device class names if no name is 
> > > >> >> specified.
> > > >> > What do you mean by "device class name". We can do something like 
> > > >> > this:
> > > >> > if (dev->child_bus.lh_first)
> > > >> >        return dev->child_bus.lh_first->info->name;
> > > >> >
> > > >> > i.e if there is child bus use its bus name as fw name. This will make
> > > >> > all pci devices to have "pci" as fw name automatically. The problem 
> > > >> > is
> > > >> > that theoretically same device can provide different buses.
> > > >>
> > > >> I meant PCI class name, like "display" for display controllers,
> > > >> "network" for NICs etc.
> > > >>
> > > > That is what my pci bus related patch is doing already.
> > > >
> > > >> >> I'll try Sparc32 to see how this fits there.
> > > >>
> > > >> Except bootindex is not implemented for SCSI.
> > > > Will look into adding it.
> > > 
> > > Thanks. The bootindex on Sparc32 looks like this:
> > > bootindex /address@hidden/address@hidden,0
> > > /address@hidden/address@hidden
> > > 
> > For arches other then x86 there is a lot of work left to be done :)
> > For starter exotic sparc buses should get their own get_fw_dev_path()
> > implementation.
> > 
> > > I don't think I got Lance setup right.
> > > 
> > > OF paths for the devices would be:
> > > /address@hidden,10000000/address@hidden,10001000/address@hidden,8400000/address@hidden,8800000/address@hidden,0
> > > /address@hidden,10000000/address@hidden,10001000/address@hidden,8400010/address@hidden,8c00000
> > If qdev hierarchy does not correspond to real HW there is no much we can
> > do expect for fixing qdev.
> 
> That's bad.  This raises a concern: if these paths expose qdev
> internals, any attempt to fix this will break migration.
> 
The path expose internal HW hierarchy. It is designed to do so. Qdev
designed to do the same: describe HW hierarchy. If qdev fails to do so it
is broken. I do not see connection to migration at all since the path is
not used in migration code.

> > > 
> > > The logic for ESP is that ESP (registers at 0x78800000, slot offset
> > > 0x880000) is handled by the DMA controller (registers at 0x78400000,
> > > slot offset 0x840000), they are in a SBus slot #5, and SBus (registers
> > > at 0x10001000) is in turn handled by IOMMU (registers at 0x10000000).
> > > Lance should be handled the same way.
> > > 
> > > This hierarchy is partly known by QEMU because DMA accesses use this
> > > flow, but not otherwise. There is no concept of SBus slots, DMA talks
> > > to IOMMU directly. Though in this case both ESP, Lance and their DMA
> > > controllers are on board devices in a MACIO chip. It may be possible
> > > to add the hierarchy information at each stage.
> > > 
> > > It should also be possible for BIOS to determine the device just from
> > > the physical address if we ignored OF compatibility.
> > It would be nice to be OF compatible at least at some level. Of course OF
> > spec is not strict enough to have two different implementations produce
> > exactly same device path that can be compared by strcpy.  Can we apply
> > the series now? At least for x86 it provides useful paths and work can
> > be continue for other arches by interested parties.
> > 
> > --
> >                     Gleb.
> 
> Something I only now realized is that we commit
> to never changing the paths for any architecture
> that supports migration.
> 
No connection to migration whatsoever.

--
                        Gleb.