Re: [Qemu-devel] [PATCH] initialize unit id of IDE bus

[Gleb Natapov <gleb@redhat.com>]

On Tue, Oct 26, 2010 at 11:14:20AM +0200, Markus Armbruster wrote:
> Gleb Natapov <gleb@redhat.com> writes:
> 
> > On Mon, Oct 25, 2010 at 06:22:12PM +0200, Markus Armbruster wrote:
> >> Gleb Natapov <gleb@redhat.com> writes:
> >> 
> >> > On Mon, Oct 25, 2010 at 04:29:35PM +0200, Markus Armbruster wrote:
> >> >> Gleb Natapov <gleb@redhat.com> writes:
> >> >> 
> >> >> > Without this patch both buses on PIIX3_IDE device have the same unit id.
> >> >> 
> >> >> Are you sure that's wrong?
> >> >> 
> >> > So how do I know which bus is it on PIIX3_IDE?
> >> [...]
> >> 
> >> Let me try to explain the IDE pointer thicket.
> >> 
> >> piix3-ide provides two IDE buses.  pci_piix_ide_initfn() stores them in
> >> PCIIDEState member IDEBus bus[2].  Technically redundant, because qdev
> >> stores child buses in dev.qdev.child_bus.
> >> 
> >> IDEBus points back: qbus.parent.
> >> 
> >> Up to two IDE devices can sit on each IDE bus.  The first one uses
> >> IDEBus members master and ifs[0], the second one uses slave and ifs[1].
> >> 
> >> ifs[i].bus points back to the IDE bus.
> >> 
> >> {master,slave}.qdev.parent_bus point back to the IDE bus.
> >> 
> >> Say you got an IDEDevice and want to know which to which of the two
> >> buses it's connected.  Let's call it d.
> >> 
> >> d->qdev.parent_bus is the BusState.
> >> 
> >> Upcast to IDEBus: b = DO_UPCAST(IDEBus, qbus, d->qdev.parent_bus).
> >> 
> >> b->qbus.parent is the IDE controller.
> >> 
> >> Upcast to PCIIDEState: c = DO_UPCAST(PCIIDEState, dev, n->qbus.parent);
> >> 
> > This will not work if IDEBus sits on ISA bus. Any other ideas?
> >
> >> If c->bus[0] == b, it's on the first bus.
> >> 
> >> Else it must be on the second bus, i.e. c->bus[1] == b.
> 
> Well, you asked for piix3-ide specifically :)
> 
No I didn't.

> isa-ide provides just one IDE bus.  Thus we have two isa-ide devices.
> To find them, you need to walk the ISA devices.  Our PCish machines have
> just one ISA bus, and it's called "isa.0".  You could try
> 
>     bus = qbus_find("isa.0");
>     QLIST_FOREACH(dev, &bus->children, sibling) {
>         // examine dev
>         // it's safe to upcast dev to ISADevice
>     }
> 
> Perhaps best to have some means in qdev.h to iterate over a bus like
> that.
> 
> If dev->info->name is "isa-ide", you found one of the controllers.
> 
When I am on IDEBus level I shouldn't care what bus it resides on to
figure out its properties. The things you describe here just show qdev
failure to provide reasonable device abstraction for IDEBus.
 
> How to tell whether it's primary or secondary?  Primary uses I/O ports
> 0x1f0..0x1ff,0x3f0..0x3ff and IRQ 14.  IRQ could be easier to check,
> because it should be right in ISADevice member isairq[0].
> Alternatively, upcast to ISAIDEState and check members iobase or isairq.
Again idebus_dev_path() should not care about what device IDEBus resides on.

> 
> 
> Hmm, there's a way that doesn't require special-casing the IDE
> controller devices: find the IDEBus as above.  Then check the IRQ#
> b->irq->n: 14 is primary, 15 is secondary.
Instead of this horrible hack (which may work, but only for PC), why not
add bus_id to IDEBus and be done with it. I already have the patch.

--
			Gleb.