radeon: RFC speed cap detection on ppc64

[Bjorn Helgaas]

On Mon, Oct 22, 2012 at 9:44 AM, Alan Cox <alan at lxorguk.ukuu.org.uk> wrote:
>> That (walking all parent nodes) is probably the safest thing to do.  I'm
>> not sure whether it's optimal.  It would likely depend on whether you
>> can meaningfully have a bridge that's faster on the downstream side than
>> on the upstream.
>
> This is architecture goo at heart - would this be better as a helper in
> the PCI and arch PCI code ?

Good point.

POWER is not the only architecture where host bridges do not appear as
devices in PCI config space -- ia64 has that, too.  So the comment is
too specific.

The link is a point-to-point thing, so this should be a local
negotiation between the radeon device and the upstream bridge.  I
don't see the point of walking any farther up the chain.

drm_pcie_get_speed_cap_mask() should also be changed to use
pcie_capability_read_dword() to avoid any issues with v1/v2 PCI
Express Capability structures.

Bjorn