Re: [Qemu-devel] Memory API: handling unassigned physical memory

[Mark Cave-Ayland]

On 30/04/12 14:23, Avi Kivity wrote:

Hi Avi,

> > My understanding based upon this is that it would be impossible to
> > register a different parent MemoryRegion without duplicating the init
> > function for all shared devices which seems undesirable :(
>
> What are the requirements?  You need a different catch-all mmio handler
> for each slot?  Or would one catch-all mmio handler for all sysbus
> devices suffice?

A single catch-all for all sysbus devices would suffice, however I'm 
thinking it makes sense to have one MemoryRegion per slot so that the 
devices can register onto the bus using their "slot relative" address to 
allow for potentially moving hardware between slots.

> > The only solution I can think of is to make sysbus_mmio_map() more
> > intelligent so that instead of blindly adding the device to the "root"
> > MemoryRegion, it traverses down the MemoryRegion hierarchy starting
> > from the root to the furtherest leaf node it can find based upon the
> > specified address and then adds the new subregion there. Hence if I
> > add my SBus memory regions first before call the various peripheral
> > init functions, everything should end up in the correct part of the
> > memory tree.
>
> This solution attempts to reconstruct the memory hierarchy from the
> address, instead of maintaining it in the device tree.

So I guess that is bad...

> > I believe this should preserve compatibility for existing sysbus API
> > users with just a single "root" MemoryRegion, however due to lack of
> > any documentation related to sysbus I'm not sure if this would break
> > other platforms or maybe even violate one of its key design features?
>
> IMO the best fix is to unsysbus the device and qomify it instead.  This
> way we're 100% flexible in how we can attach it.

That's interesting - I didn't realise that sysbus is a legacy interface 
with respect to QOM. Is there any documentation related to this? Then 
again, converting all of the devices over to QOM and testing that it 
doesn't break all platforms/busses suddenly becomes a huge job...


ATB,

Mark.