ACPI vs PCI: configuration space

OK, I've been bashing my head against this for two days, it's time to get more eyes on the problem. The problem is in acpi_os_read_pci_configuration() and acpi_os_write_pci_configuration(). These functions can be called for busses which have not yet been scanned (and therefore do not have a corresponding pci_bus). The code in 2.5 doesn't work for ia64 beause we need a valid ->sysdata pointer to handle PCI domains.

The current patch in the ia64 tree does this:

        struct pci_bus          bus;

+#ifdef CONFIG_IA64
+ struct pci_controller ctrl;
+#endif

...

        bus.number = pci_id->bus;

+#ifdef CONFIG_IA64
+ ctrl.segment = pci_id->segment;
+ bus.sysdata = &ctrl;
+#endif

        result = pci_root_ops->read(&bus, PCI_DEVFN(pci_id->device,

I think we can all agree that's ugly. But there's no _clear_ way to improve this.

Try 1: Ask the architecture code to provide a sysdata for us. That's bad; it needs to allocate with GFP_ATOMIC (since this code can be called from interrupt context). So it can fail on low mem conditions.

Try 2: Define a `struct pci_controller' on architectures that don't have it. And a macro pci_set_domain() so x86 can have a zero-length pci_controller. Not the prettiest idea, but best of this batch.

Try 3: Move the segment/domain into the pci_bus. This already got NAKed by a few people.

Try 4: redefine the pci_ops again. Haha, very funny.

It's kind of annoying to invent some structures and put some values into them only to pull them out again. This leads to try 5 ...

struct acpi_pci_ops {
	int (*read)(int domain, int bus, int devfn, int where, int size, u32 *val);
	int (*write)(int domain, int bus, int devfn, int where, int size, u32 val);
}

It reduces stack consumption, which is a clear win ... it's also _incredibly_ easy to implement since all the existing pci_ops call functions which take exactly this form.

Go on, approve Try 5. You know you want to ;-)

"It's not Hollywood.  War is real, war is primarily not about defeat or
victory, it is about death.  I've seen thousands and thousands of dead bodies.
Do you think I want to have an academic debate on this subject?" -- Robert Fisk

So for i386, what would domain be?

Anyway, yeah, I agree with try 5, that seems the most sane.

thanks,

greg k-h

The `seg' argument currently in place to all these macros ;-)

Yay. you'll have a patch tomorrow.

"It's not Hollywood.  War is real, war is primarily not about defeat or
victory, it is about death.  I've seen thousands and thousands of dead bodies.
Do you think I want to have an academic debate on this subject?" -- Robert Fisk