Port of Linux commit 6d6b05e

    The DWC PCIe core contains various separate register spaces: DBI, DBI2,
    ATU, DMA, etc. The relationship between the addresses of these register
    spaces is entirely determined by the implementation of the IP block, not
    by the IP block design itself. Hence, the DWC driver must not make
    assumptions that one register space can be accessed at a fixed offset from
    any other register space. To avoid such assumptions, introduce an
    explicit/separate register pointer for the ATU register space. In
    particular, the current assumption is not valid for NVIDIA's T194 SoC.

    The ATU register space is only used on systems that require unrolled ATU
    access. This property is detected at run-time for host controllers, and
    when this is detected, this patch provides a default value for atu_base
    that matches the previous assumption re: register layout. An alternative
    would be to update all drivers for HW that requires unrolled access to
    explicitly set atu_base. However, it's hard to tell which drivers would
    require atu_base to be set. The unrolled property is not detected for
    endpoint systems, and so any endpoint driver that requires unrolled access
    must explicitly set the iatu_unroll_enabled flag (none do at present), and
    so a check is added to require the driver to also set atu_base while at
    it.

    Signed-off-by: Stephen Warren <swarren@nvidia.com>
    Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
    Acked-by: Gustavo Pimentel <gustavo.pimentel@synopsys.com>
    Acked-by: Vidya Sagar <vidyas@nvidia.com>

Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>