USB: Don't fail USB3 probe on missing legacy PCI IRQ.

USB: Don't fail USB3 probe on missing legacy PCI IRQ.

commit 68d07f64b8a11a852d48d1b05b724c3e20c0d94b upstream

Intel has a PCI USB xhci host controller on a new platform. It doesn't
have a line IRQ definition in BIOS.  The Linux driver refuses to
initialize this controller, but Windows works well because it only depends
on MSI.

Actually, Linux also can work for MSI.  This patch avoids the line IRQ
checking for USB3 HCDs in usb core PCI probe.  It allows the xHCI driver
to try to enable MSI or MSI-X first.  It will fail the probe if MSI
enabling failed and there's no legacy PCI IRQ.

This patch should be backported to kernels as old as 2.6.32.

[Maintainer note: This patch is a backport of commit
68d07f64b8a11a852d48d1b05b724c3e20c0d94b "USB: Don't fail USB3 probe on
missing legacy PCI IRQ." to the 3.0 kernel.  Note, the original patch
description was wrong.  We should not back port this to kernels older
than 2.6.36, since that was the first kernel to support MSI and MSI-X
for xHCI hosts.  These systems will just not work without MSI support,
so the probe should fail on kernels older than 2.6.36.]

Signed-off-by: Alex Shi <alex.shi@intel.com>
Signed-off-by: Sarah Sharp <sarah.a.sharp@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>