Comment 29 for bug 1536397

It was impossible to resist temptation to find where the story began. It all started between 4.1 and 4.2-rc1. Bisecting points to this commit:

3d9fecf6bfb8b12bc2f9a4c7109895a2a2bb9436 is the first bad commit
commit 3d9fecf6bfb8b12bc2f9a4c7109895a2a2bb9436
Author: Bjorn Helgaas <email address hidden>
Date: Tue Jun 9 17:31:38 2015 -0500

    x86/PCI: Use host bridge _CRS info on systems with >32 bit addressing

    We enable _CRS on all systems from 2008 and later. On older systems, we
    ignore _CRS and assume the whole physical address space (excluding RAM and
    other devices) is available for PCI devices, but on systems that support
    physical address spaces larger than 4GB, it's doubtful that the area above
    4GB is really available for PCI.

    After d56dbf5bab8c ("PCI: Allocate 64-bit BARs above 4G when possible"), we
    try to use that space above 4GB *first*, so we're more likely to put a
    device there.

    On Juan's Toshiba Satellite Pro U200, BIOS left the graphics, sound, 1394,
    and card reader devices unassigned (but only after Windows had been
    booted). Only the sound device had a 64-bit BAR, so it was the only device
    placed above 4GB, and hence the only device that didn't work.

    Keep _CRS enabled even on pre-2008 systems if they support physical address
    space larger than 4GB.

    Fixes: d56dbf5bab8c ("PCI: Allocate 64-bit BARs above 4G when possible")
    Reported-and-tested-by: Juan Dayer <email address hidden>
    Reported-and-tested-by: Alan Horsfield <email address hidden>
    Link: https://bugzilla.kernel.org/show_bug.cgi?id=99221
    Link: https://bugzilla.opensuse.org/show_bug.cgi?id=907092
    Signed-off-by: Bjorn Helgaas <email address hidden>
    CC: <email address hidden> # v3.14+