Re: a7839e96 (PNP: increase max resources) breaks my ALSA intel8x0 sound card

Linus Torvalds
2008-02-04T21:18:42Z

On Mon, 4 Feb 2008, Bjorn Helgaas wrote:
>
> I'm sure you're right, but I don't understand why yet. Here's what
> I think is happening; please correct me where I'm going wrong:
>
> 1) enumerate PNP & ACPI devices
> 2) initialize PNP & ACPI drivers
> 2a) register ACPI PCI root bridge driver, which enumerates PCI
> devices behind the bridge
> 2b) register PNP system driver and reserve resources (this is
> where the current quirk skips some reservations)
> 3) initialize PCI drivers
> 3a) register intel8x0 sound driver and reserve conflicting
> resources

So where in this would you put the

pcibios_init() -> pcibios_resource_survey()

call (it's a subsys_initcall)?

THAT is the thing that actually registers the PCI resurces we've found
into the resource tree!

It's very inconveniently placed as-is, since it literally depends on the
whole initcall ordering (and the link order within that subsys_initcall
thing), and all of this is architecture-driven rather than driven from
some central place.

So this is the thing that I think should happen before any PnP or ACPI
drivers actually start registerign themselves (but obviously needs to
happen after the PCI buses have been enumerated).

The ACPI/PnP tables shouldn't be able to break the enumeration of the
actual hardware devices, now should it?

> I think you're suggesting that we should do 2a first, to enumerate all
> PCI devices, and only later do 2b. But I don't know how to accomplish
> that cleanly.

We should enumerate the PCI devices, then register their resources (and
no, I'm not at *all* convinced it should happen as a separate
subsys_initcall), and then register the PnP resources.

So I think we should have roughly something like:

- arch_initcall: this could enumerate the ACPI/PnP devices (but not
register anything). Alternatively, do it as subsys_initcall, and just
make sure it happens early with link-order.

- subsys_initcall: this should do that pcibios_init() thing that surveys
the resources (and the PCI enumeration needs to have happened before,
probably in the same initcall thanks to link order)

- PnP/ACPI resource allocation *after* it, but before driver loading
(which wll cause new resources to be allocated). This could be
fs_initcall, or whatever (that's what things like "acpi_event_init"
already do).

- regular drivers will come along much later, as part of
driver_initcall, and by the time this happens, we've now reserved all
resources we know about.

Basically, we just want to register the most trust-worthy resources before
we register anything less trust-worthy. And actual device probing simply
tends to be more trust-worthy than any randomly broken ACPI/PnP tables.

Linus