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


From: Markus Armbruster
Subject: Re: [Qemu-devel] [PATCH] initialize unit id of IDE bus
Date: Tue, 26 Oct 2010 11:14:20 +0200
User-agent: Gnus/5.13 (Gnus v5.13) Emacs/23.1 (gnu/linux)

Gleb Natapov <address@hidden> writes:

> On Mon, Oct 25, 2010 at 06:22:12PM +0200, Markus Armbruster wrote:
>> Gleb Natapov <address@hidden> writes:
>> 
>> > On Mon, Oct 25, 2010 at 04:29:35PM +0200, Markus Armbruster wrote:
>> >> Gleb Natapov <address@hidden> 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 :)

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.

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.


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.



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