commit 8505e729 upstream.

Add pci_claim_bridge_resource() to claim a PCI-PCI bridge window.  This is
like regular pci_claim_resource(), except that if we fail to claim the
window, we check to see if we can reduce the size of the window and try
again.

This is for scenarios like this:

  pci_bus 0000:00: root bus resource [mem 0xc0000000-0xffffffff]
  pci 0000:00:01.0:   bridge window [mem 0xbdf00000-0xddefffff 64bit pref]
  pci 0000:01:00.0: reg 0x10: [mem 0xc0000000-0xcfffffff pref]

The 00:01.0 window is illegal: it starts before the host bridge window, so
we have to assume the [0xbdf00000-0xbfffffff] region is inaccessible.  We
can make it legal by clipping it to [mem 0xc0000000-0xddefffff 64bit pref].

Previously we discarded the 00:01.0 window and tried to reassign that part
of the hierarchy from scratch.  That is a problem because Linux doesn't
always assign things optimally.  For example, in this case, BIOS put the
01:00.0 device in a prefetchable window below 4GB, but after 5b285415,
Linux puts the prefetchable window above 4GB where the 32-bit 01:00.0
device can't use it.

Clipping the 00:01.0 window is less intrusive than completely reassigning
things and is sufficient to let us use most of the BIOS configuration.  Of
course, it's possible that devices below 00:01.0 will no longer fit.  If
that's the case, we'll have to reassign things.  But that's a separate
problem.

[bhelgaas: changelog, split into separate patch]
Link: https://bugzilla.kernel.org/show_bug.cgi?id=85491Reported-by: Marek Kordik <kordikmarek@gmail.com>
Fixes: 5b285415 ("PCI: Restrict 64-bit prefetchable bridge windows to 64-bit resources")
Signed-off-by: Yinghai Lu <yinghai@kernel.org>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Signed-off-by: Luis Henriques <luis.henriques@canonical.com>