Re: [Qemu-devel] modelling omap_gpmc with the hierarchical memory API

[Peter Maydell]

On 2 August 2011 19:05, Avi Kivity <address@hidden> wrote:
> On 08/02/2011 08:21 PM, Peter Maydell wrote:
>> So I think we just need a sysbus_mmio_get_memoryregion()
>> (and convert the devices I need to attach to use memory
>> regions, and live with not being able to attach unconverted
>> devices).
>
> I don't follow - why do we need get_memoryregion? who would call it?

The machine model would call it. So you do something like
 DeviceState *dev = qdev_create(NULL, "whatever");
 /* Note the parallel here to the existing
  *   sysbus_mmio_map(sysbus_from_qdev(dev), mmio_idx, addr);
  */
 MemoryRegion *mr =
sysbus_mmio_get_memoryregion(sysbus_from_qdev(dev), mmio_idx);
 omap_gpmc_attach(gpmc, 7, mr);

ie the machine model is where we wire up the subdevices
to the gpmc, and at the machine model level what you have is
a pointer to an entire device, so you need to be able to
convert the (sysbus*, mmio_index) tuple to a MemoryRegion*.

>> [That is, the only reason I'm passing SysBus objects around
>> is that at the moment that is the only useful abstraction we
>> have for saying "I'm an arbitrary device object and I provide
>> some GPIO pins and some memory mappable regions". MemoryRegion*
>> allows me to pass around a memory mappable region in a more
>> direct way than having to pass a (SysBus*, mmio_index) tuple.]
>
> I think I see.  Perhaps you're describing qdev/MemoryRegion integration.

I think qdev devices need to be able to expose MemoryRegions
as first class named 'properties' or 'plugs' or 'sockets' or
whatever we want to call them, yes. (Ditto gpio/irq, which at
the moment we can kind of expose but not by name.)

-- PMM