[RESEND PATCH 1/3] pci_auto: Downgrade prefetch if necessary

[Tom Rini]

On Mon, Mar 10, 2025 at 10:01:32AM +0100, Patrick Rudolph wrote:

> 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 at 9elements.com>

Do we need this series for v2025.04 or v2025.07? Thanks!

-- 
Tom
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