On 08/02/2011 01:21 PM, Peter Maydell wrote:
On 2 August 2011 19:05, Avi Kivity<a...@redhat.com> 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*.
Hrm, this looks like badness to me.
You're effectively using MemoryRegions to implement an ad-hoc interface.
This is not what MemoryRegions are meant to do though. You want
something like:
class WhateverDevice : public Device, implements SimpleDevice
{
MemoryRegion *get_memory_region(void);
};
class OmapGmc : public Device
{
SimpleDevice *slots[8];
};
In qdev of today, you should implement something other than SysBus as a
base class and make OmapGmc a bus.
[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.)
I disagree in this case. I think MemoryRegion is a bit too low level of
a connecting point. I think an interface would be a stronger interface
to use.
What's the relationship between the omap_gpmc and the devices in real
hardware? Are the devices designed to connect to the GPMC explicitly
via a common set of pins? Is there an intermediate bridge chip or
something?
Regards,
Anthony Liguori
-- PMM
