Legacy PCI devices, like qemu's Bochs VGA device, are allowed to have
prefetchable 32-bit BARs, while PCIe devices are not allowed to have
32-bit prefetchable BARs. Typically prefetchable BARs are 64-bit and
typically the prefetch MMIO window is also 64-bit and placed above
4GiB, as it's the case on qemu sbsa-ref.
Currently the U-Boot code assumes that prefetchable BARs are
64-bit BARs and always tries to assign them into the prefetch
MMIO window.
When a 32-bit BAR is marked as prefetch, but the prefetch area is
not within the first 4GiB of the address space, then downgrade the
BAR and place it in the non-prefetch MMIO window.
For prefetch BARs there's no downside on being placed in non prefetch
MMIO areas, besides the possible slower performance when a driver tries
to map it Write-Combine.
TEST: Fixes pci_auto on QEMU sbsa-ref fails to autoconfigure BAR0.
Signed-off-by: Patrick Rudolph <patrick.rudolph@9elements.com>
Patrick Rudolph
699baa63dd